The specimen examined is BSPG 1991 II 130, the holotype of Allaeochelys libyca , held by the Bayerische Staatssammlung für Paläontologie und Geologie in Munich. It is an incomplete cranium from the Lower Maradah Formation at Gebel Zelten, also called Jabal Zaltan, in southwestern Libya. The locality has been assigned to the Langhian stage of the Middle Miocene.

The species was originally described in 2014 from this partial skull and several isolated shell fragments. That earlier work described the externally visible anatomy, but the internal cavities, canals and other structures could not be examined directly. The new reassessment began when the researchers downloaded the specimen’s micro-CT slice data from the MorphoSource repository and noticed that their three-dimensional reconstructions differed from the original interpretation of some features.

The fossil had been scanned at the University of Bristol’s X-ray Tomography Facility using a Nikon Metrology XT H 225 ST scanner at 125 kV and 265 µA. The scan produced 1,601 projections and 1,813 coronal slices with a voxel size of 37.8 µm. The researchers segmented individual bones in Mimics Innovation Suite 25, exported the objects as PLY files and visualized them in Blender 2.79b.

The resulting cranium and inner-ear models were also deposited at MorphoSource, making the digital reconstruction available for further study. One of the most consequential revisions concerns the opening that the original description called the “posterior” trigeminal nerve foramen. The CT data show that it communicates with the cavum acustico-jugulare, a chamber associated with the inner ear and major cranial nerves, rather than opening directly into the braincase in which the trigeminal nerve originates.

Comparisons with the living pig-nosed turtle, Carettochelys insculpta , indicate that the fossil opening represents the posterior portion of a broader passage associated with both the trigeminal nerve and the mandibular artery. The authors distinguish the true trigeminal foramen from the posterior mandibular artery foramen, while noting that the two are homologous with the combined “trigeminal foramen sensu lato” of the living species. Reconstructing the missing epipterygoid is essential to that interpretation.

Havlik and colleagues had identified a purported epipterygoid beneath the processus trochlearis oticum and between the two openings, but the CT slices show that the apparent sutures around this piece are actually a crack. The bone is not preserved. A small, anteroventrally projecting bump on the fossil’s prootic, however, matches the articular site for the epipterygoid in Carettochelys insculpta .

This supports the inference that the missing bone formed a narrow bridge around a strongly reduced canalis cavernosus. In the living turtle, that canal is closely associated with the lateral head vein, while the fossil suggests that the mandibular artery could pass from the inner-ear region into the lower temporal fossa. The authors consider complete loss of the canal in Allaeochelys followed by its reappearance in Carettochelys less likely than preservation of a reduced canal obscured by the missing epipterygoid.

The scans also clarify the circulatory routes through the skull. The posterior opening of the internal carotid canal lies entirely within the pterygoid, rather than in the more anteroventral position occupied by the corresponding foramen in the early-branching carettochelyids Anosteira pulchra and Anosteira maomingensis . From this opening, the internal carotid canal extends anteromedially through the pterygoid and continues into the parabasisphenoid as the basisphenoidal carotid canal.

A branch of the facial nerve for the vidian nerve joins the internal carotid canal, while a separate canal carries the abducens nerve through the parabasisphenoid. As in Carettochelys insculpta and Anosteira pulchra , no lateral carotid canal is present. The reconstructed arterial and nervous routes are therefore similar across these taxa, even though the position of the posterior carotid opening differs in A. libyca .

Neural anatomy also yielded a correction to the count of hypoglossal foramina. The original description recognized three external openings for the hypoglossal nerves, but tomography reveals only two distinct sets of internal and external foramina, together with their associated canals. The supposed third external opening is exposed surface porosity rather than a nerve passage.

The two-foramina condition matches the living Carettochelys insculpta and the fossil Anosteira pulchra . The reinterpretation also places the nearly horizontal suture between the exoccipital and basioccipital farther ventrally than in the original description, although the seam fades toward the posterior and was therefore difficult to follow without tomographic data. The endosseous labyrinth, the bony housing of the inner ear, is among the structures newly documented in detail.

Its semicircular canals are thick, with the anterior canal the longest and the lateral canal the shortest. The anterior canal joins the vestibule at the level of the anterior ampulla. The posterior canal is shorter, and its posterior third is confluent with the posterior part of the lateral canal, creating a large secondary common crus.

The lateral canal forms a proper canal only along its posterior half and merges anteriorly with a large lateral ampulla. The fossil labyrinth is extremely similar to that of the fully segmented Carettochelys insculpta specimen NHMUK 1903.7.10.1. Only two subtle differences were identified: the anterior semicircular canal of the fossil is slightly thicker, and the dorsal embayment of the common crus is slightly more deeply excavated.

Other findings refine the skull’s construction. A secondary contact between the frontal and prefrontal appears to create a passage between the orbit and nasal cavity, a condition also reported in the Middle Miocene Carettochelys niahensis but absent in the living species. The fossil also possesses an anterior quadrate foramen and a short canal that the authors name as a potential shared feature of derived carettochelyids; its precise identity remains uncertain because no connection with the columella auris or the cavum acustico-jugulare could be demonstrated.

A large recessus scalae tympani, a possible glossopharyngeal nerve canal in the opisthotic, and the arrangement of the jugular and hypoglossal foramina were also reconstructed. These observations remain constrained by missing premaxillae, maxillae, jugals, vomer, squamosals and other damaged elements, as well as the loss of much of the epipterygoid and anterior braincase. The anatomical revisions do not challenge Allaeochelys libyca as a valid species.

Its broader and shorter cranium, secondary prefrontal–frontal contact, deeper pterygoid fossa, larger quadrate fossa, reduced canalis cavernosus and other traits continue to distinguish it from Carettochelys insculpta . The authors do expect the redescription to affect phylogenetic matrices, where several character scorings will need revision and additional features may be added, including the prefrontal–frontal contact, the possible glossopharyngeal canal and the relative length of the basioccipital tubercles. Although these changes are not expected to produce a drastic rearrangement of carettochelyid relationships, they may help resolve subclades that have remained uncertain, including the groups containing Anosteira and Allaeochelys .

The study demonstrates how a single damaged fossil can preserve a detailed record of sensory, neural and vascular anatomy that was previously hidden inside a skull.

Subject of Research: Digital tomographic redescription of the Middle Miocene carettochelyid turtle Allaeochelys libyca

Article Title: A digital redescription of the Middle Miocene (Langhian) carettochelyid turtle Allaeochelys libyca

Article References: Rollot, Y., Evers, S. W., & Joyce, W. G. (2024). A digital redescription of the Middle Miocene (Langhian) carettochelyid turtle Allaeochelys libyca. Fossil Record, 27(1), 13-28. https://doi.org/10.3897/fr.27.115046

Image Credits: AI Generated

DOI: 10.3897/fr.27.115046

Keywords: Allaeochelys libyca, Carettochelyidae, micro-computed tomography, fossil skull anatomy, Miocene turtle, paleontology, inner ear, cranial nerves, digital reconstruction, Libya, digital, redescription

Imipenem was the first carbapenem antibiotic to reach clinical use, and it is paired with cilastatin, a molecule that blocks renal degradation of imipenem and prolongs its activity in the body. Carbapenems are often described as last-line agents, deployed when other antibiotics fail or when bacteria produce enzymes that destroy common drugs. Their most recognized adverse effects are neurological: seizures, confusion, and other central nervous system disturbances, particularly at high doses or in patients with kidney impairment. Hearing loss, by contrast, has rarely been reported with this class, which is why the authors of the new report conducted a literature review alongside their case description to see whether similar events had been documented before.

The patient in the report was being treated for an abdominal infection complicating liver cancer and cirrhosis. Within a day of receiving intravenous imipenem/cilastatin, the patient reported subjective hearing loss on the right side. Importantly, the loss was never confirmed with objective audiological testing such as pure-tone audiometry or high-frequency audiometry, the standard tools for measuring hearing thresholds. This absence of objective measurement is a central limitation the authors themselves acknowledge. Subjective complaints of hearing change can arise from many causes in a critically ill, older patient, including the infection itself, other drugs, or fluctuations in attention and perception that are difficult to disentangle at the bedside.

To assess how plausible a drug-related cause was, the team applied two standard pharmacovigilance tools: the WHO-UMC causality system and the Naranjo scale. Both frameworks weigh factors such as the timing of the reaction relative to drug exposure, whether the reaction improved when the drug was stopped, whether it recurred on re-exposure, and whether alternative explanations exist. In this case, the temporal relationship was strong, with symptoms appearing within 24 hours of the first dose, and the improvement after discontinuation supported a possible link. However, the patient was never re-exposed to the antibiotic, and the concurrent use of furosemide, a loop diuretic with well-established ototoxic potential, meant that causality could not be established with certainty. The authors characterized the association as possible rather than probable, and they explicitly note that alternative explanations, particularly furosemide exposure, cannot be excluded.

Furosemide deserves particular attention in this context. Loop diuretics are among the classic ototoxic drugs in medicine, capable of damaging the stria vascularis and outer hair cells of the cochlea, especially when given intravenously at high doses or in patients with kidney dysfunction. The blood-labyrinth barrier, a specialized barrier that separates the inner ear from the bloodstream, normally shields the delicate sensory cells of the cochlea from many circulating substances, but certain drugs can cross it or disrupt it. When a patient receives both a carbapenem and a loop diuretic simultaneously, attributing a hearing change to one agent rather than the other becomes genuinely difficult. This pharmacological ambiguity is precisely why the authors stopped short of declaring imipenem/cilastatin the culprit, even though the timing pattern favored it.

The literature review accompanying the case report adds context to how rarely hearing loss has been tied to carbapenems. Most documented ototoxicity in antibiotic therapy involves aminoglycosides such as gentamicin and amikacin, which accumulate in cochlear fluid and can cause permanent, often irreversible damage to hair cells. Vancomycin, particularly when combined with aminoglycosides, has also been implicated. Carbapenems, by contrast, have a safety profile dominated by neurological and gastrointestinal effects rather than auditory ones. The rarity of prior reports means that a single case, however suggestive, cannot establish a pattern. What it can do is alert clinicians and pharmacologists to a possibility worth monitoring, especially in patients receiving multiple potentially ototoxic drugs at once.

The clinical implications of this report are practical rather than dramatic. For physicians prescribing imipenem/cilastatin, the case suggests that new hearing complaints during treatment should be taken seriously, documented carefully, and evaluated with objective audiological testing whenever feasible. For pharmacists and hospital safety committees, it reinforces the value of reviewing concomitant medications when an adverse reaction appears, since the presence of furosemide here complicated the causal picture considerably. For regulators and pharmacovigilance databases, single case reports like this one function as early signals that may prompt further investigation if similar cases accumulate. The authors emphasize that their findings warrant clinical attention and further investigation rather than any change in prescribing practice.

From a mechanistic standpoint, the report raises interesting questions about how a carbapenem could theoretically affect the inner ear. The blood-labyrinth barrier restricts drug entry into cochlear fluids, but it is not absolute, and factors such as inflammation, infection, and kidney dysfunction can alter its permeability. Patients with cirrhosis and severe abdominal infections often have altered drug metabolism and clearance, which can raise drug concentrations in ways that are difficult to predict. Whether imipenem or its metabolites can reach ototoxic concentrations in the cochlea under such conditions remains unknown, and the authors do not claim a mechanism. What they offer instead is a carefully documented temporal association, an honest accounting of confounders, and a call for systematic audiological monitoring in similar patients.

The case also illustrates a broader tension in modern pharmacovigilance. Objective testing, such as pure-tone audiometry and high-frequency audiometry, provides the gold standard for confirming hearing loss, yet it is often impractical in acutely ill patients on complex antibiotic regimens. Subjective reports, meanwhile, are common and meaningful to patients but difficult to verify. The authors of this report are transparent about this gap, noting that no objective audiological assessment was performed and that the hearing loss remained subjectively confirmed only. Their use of the WHO-UMC system and the Naranjo scale reflects an effort to bring structure to an inherently uncertain judgment, and their conclusion that causality cannot be established with certainty is a model of careful causal reasoning in a single-patient report.

For now, imipenem/cilastatin remains a critical tool against severe and drug-resistant infections, and this single case does not change that. What it does change is the level of awareness among clinicians who use it. A patient who suddenly reports hearing changes while receiving this antibiotic, particularly alongside other potentially ototoxic drugs, now has a documented precedent that clinicians can consult. The report, published open access in BMC Infectious Diseases by a team from the Department of Pharmacy and the Department of Infectious Diseases at Longyan Second Hospital in Fujian, China, adds a small but carefully reasoned data point to the pharmacological record. As the authors conclude, the association between imipenem/cilastatin exposure and subjective hearing loss remains possible but unconfirmed, and it is precisely this kind of disciplined uncertainty that allows rare adverse drug signals to be recognized without overstating the evidence behind them.

Subject of Research: Possible association between the carbapenem antibiotic imipenem/cilastatin and hearing loss reported in a single clinical case

Article Title: Hearing loss associated with imipenem/cilastatin: a case report and literature review

Article References: Zhang, S., Liao, S., Zhang, L., Huang, Q., & Liu, H. (2026). Hearing loss associated with imipenem/cilastatin: a case report and literature review. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14657-w

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14657-w

Keywords: hearing loss, ototoxicity, imipenem/cilastatin, carbapenem antibiotics, adverse drug reaction, furosemide, pharmacovigilance, blood-labyrinth barrier, BMC Infectious Diseases, case report, antimicrobial therapy, inner ear

Obstructive sleep apnea, or OSA, is defined by repeated interruptions or reductions of breathing during sleep, each lasting more than ten seconds and occurring at least five times per hour. The condition is extraordinarily common and extraordinarily underdiagnosed. An estimated 80 to 90 percent of affected adults do not know they have it, and recent estimates place the prevalence in the United States at 32.4 percent, roughly 83.7 million people, a dramatic rise from figures recorded in the 1990s. Severity is graded by the apnea-hypopnea index, with mild disease involving 5 to 15 breathing events per hour, moderate disease 15 to 30, and severe disease 30 or more.

The review’s central question is what happens to the vestibular system, the network of fluid-filled semicircular canals and otolith organs in the inner ear that detects head motion and gravity. Vestibular dysfunction shows up objectively as a reduced vestibulo-ocular reflex gain on the video head impulse test, asymmetrical or absent vestibular-evoked myogenic potentials, or weakened caloric responses. Subjectively, it manifests as dizziness, vertigo, oscillopsia, imbalance, and a heightened risk of falls and accidents that can uproot daily life.

The evidence linking OSA to these deficits is striking. In one study, all 32 patients with moderate-to-severe OSA showed decreased vestibulo-ocular reflex gain compared with healthy controls, and patients with the most severe disease had a significantly higher fall-risk index than those with mild disease or controls. Both ocular and cervical vestibular-evoked myogenic potentials appear significantly lower in OSA patients than in healthy people, indicating damage across the semicircular canals, the saccule and the utricle. A meta-analysis from February 2025 quantified the risk: adults with OSA were significantly more likely to show abnormal vestibular testing, with an odds ratio of 4.8 for abnormal caloric tests, 7.9 for absent cervical vestibular-evoked potentials, and 6.2 for absent ocular vestibular-evoked potentials.

Why would a breathing disorder attack the inner ear? The review lays out three converging mechanisms. The ischemic theory holds that intermittent hypoxia, surging sympathetic tone, and endothelial dysfunction, including elevated levels of the vasoconstrictor endothelin, starve the labyrinth of blood. Because the inner ear is fed exclusively by terminal branches of the anterior inferior cerebellar artery with no collateral circulation, vasospasm or pressure swings can quickly translate into localized oxygen deprivation, and laboratory studies confirm that vestibular hair cells and the vestibular nucleus are vulnerable to hypoxia and reactive oxygen species.

The inflammation theory adds a second assault. Chronic inflammation in OSA releases pro-inflammatory cytokines such as tumor necrosis factor-alpha and interleukin-6, which can trigger apoptosis in vestibular hair cells and atrophy of the stria vascularis. Inflammation also activates monocytes, creating microvascular perfusion deficits within the inner ear that may locally ischemize the vestibular neuroepithelium. A third, anatomical explanation notes that the nasopharynx and oropharynx, the very segments that collapse in OSA, are crucial to eustachian tube function; repetitive mechanical stress and high negative intrathoracic pressure can disrupt middle ear pressure, disturb the endolymph and perilymph, and mechanically stimulate vestibular receptors. Recent work even links semicircular canal dysfunction to altered heart rate variability, implicating autonomic dysregulation as a mediator of the vertigo-apnea connection.

The clinical consequences ripple through three classic vestibular syndromes. Benign paroxysmal positional vertigo, the most common cause of vertigo worldwide, arises when calcium carbonate otoconia dislodge into the semicircular canals, producing brief, violent spinning triggered by head movements. Patients with OSA show significantly higher rates of BPPV than healthy controls, and a 2021 study concluded that BPPV is not a random occurrence in these patients but a systemic consequence of sleep-disordered breathing, although no study has yet screened for BPPV specifically within OSA populations.

Meniere’s disease, a chronic disorder marked by vertigo, hearing loss, tinnitus and aural fullness thought to stem from endolymphatic hydrops, is similarly entangled with sleep apnea. A 2025 study found a staggering 75 percent prevalence of OSA among Meniere’s patients, with moderate-to-severe apnea associated with greater hearing loss. A nine-year longitudinal cohort of more than one million South Koreans showed that adults aged 45 to 64 with OSA had twice the incidence of subsequent Meniere’s disease. Shared risk factors such as obesity, hypertension and metabolic syndrome, along with intermittent hypoxia stressing the blood-labyrinthine barrier, likely explain the association, while fragmented sleep worsens tinnitus.

Vestibular migraine, the leading cause of episodic non-positional vertigo, completes the triad. Among 130 patients with severe OSA, 10.8 percent had vestibular migraine, and OSA was significantly overrepresented in vestibular migraine groups compared with controls. Obesity links the two conditions biologically, and the review’s authors suggest that treating OSA may itself relieve vestibular migraine, an intriguing therapeutic hypothesis that deserves further study.

That therapeutic angle is where the story turns hopeful. Continuous positive airway pressure, the gold standard OSA treatment, keeps the airway splinted open with a steady stream of pressurized air, maintaining consistent oxygen levels and reducing oxidative stress and inflammation. Early evidence suggests CPAP may benefit vestibular function directly: a pilot study of 20 Meniere’s patients with concomitant OSA found that CPAP alone helped control dizziness and vertigo with potential hearing benefit, and CPAP use in migraine sufferers dramatically reduced attack frequency from 5.8 to 0.1 days per month alongside shorter, less painful attacks and less medication use. A 12-month study tracking vestibulo-ocular reflex gain before and after CPAP found no significant improvement yet, hinting that longer treatment windows may be needed. The authors’ prescription is twofold: patients with OSA, especially those with Meniere’s disease or BPPV, should undergo systematic vestibular screening, and anyone with unexplained balance problems should be evaluated for hidden sleep apnea. In a condition that already affects more than 80 million Americans silently, the spinning room may be the clue nobody thought to chase.

Subject of Research: The impact of obstructive sleep apnea on vestibular dysfunction, vertigo syndromes, and balance

Article Title: Vestibular dysfunction in patients with obstructive sleep apnea: from physiopathology to treatment

Article References: Jihène, M., Selima, J., Aymen, S., & Melek, D. (2026). Vestibular dysfunction in patients with obstructive sleep apnea: from physiopathology to treatment. Frontiers in Sleep, 5, Article 1750104. https://doi.org/10.3389/frsle.2026.1750104

Image Credits: AI Generated

DOI: 10.3389/frsle.2026.1750104

Keywords: obstructive sleep apnea, vestibular dysfunction, vertigo, Meniere's disease, benign paroxysmal positional vertigo, vestibular migraine, CPAP, inner ear, intermittent hypoxia, balance disorders, vestibulo-ocular reflex, fall risk

More than 150 deafness-associated genes have been identified, but their expression across human cell types remains largely descriptive and incompletely mapped. Developmental pathways are well described in animal models, yet species differences may limit their translational relevance to humans. Moreover, no established framework existed for identifying the regulatory programs that control human inner ear cell fate. Single-cell RNA sequencing has transformed our understanding of human developmental biology in organs such as the skin, but in the inner ear field most single-cell studies have focused on the mouse cochlea, leaving human inner ear development, and the distinction between cochlear and vestibular regions, poorly defined. Human pluripotent stem cell-derived inner ear organoids are valuable tools for studying human-specific cell types, but they lack key cell types essential for normal function, particularly the secretory epithelia that maintain the ionic balance of the endolymph.

Now a team led by Wouter H. van der Valk, Shantha Devi Udayappan and Heiko Locher at Leiden University Medical Center, working with colleagues in Belgium and at Boston Children’s Hospital and Harvard Medical School, has addressed these gaps with a resource they call HIEDRA, the Human Inner Ear Development snRNA-seq Atlas. Published in Nature Neuroscience, the atlas is built from single-nucleus RNA sequencing of nine human fetal inner ear samples spanning fetal weeks 7 through 15, a window that captures the critical events of cell type specification, including cochlear elongation into its characteristic spiral shape, the onset of hair cell formation around fetal week 10, and the emergence of structures such as the tectorial membrane, the stria vascularis and Reissner’s membrane. After rigorous quality control, the datasets were integrated into an atlas of 42 annotated clusters containing cochlear and vestibular epithelia, hair cells, mesenchymal populations, neurons, Schwann cells, chondrocytes, melanocytes, endothelial cells, immune cells and cycling cells.

The technical power of HIEDRA lies in its ability to resolve transcriptional identities along known spatial domains. Cochlear epithelial cells segregated along the duct floor into medial, prosensory and lateral domains, destined to form the inner sulcus and interdental cells, the organ of Corti, and the outer sulcus respectively. A similar organization was observed in the cochlear roof, where a medial region gives rise to Reissner’s membrane and a lateral region forms the marginal cells of the stria vascularis. Notably, the gene ANOS1, mutations in which cause hearing loss of unknown mechanism, was highly expressed in this lateral roof region, suggesting that ANOS1 may contribute to pathways involved in stria vascularis development. In the vestibular epithelium, supporting cells separated into ampulla-associated and otolith-associated populations, corresponding to the cristae ampullaris and the utricle and saccule, with differential expression of genes such as NEGR1, KCNIP4 and MECOM reflecting their anatomical origins.

Cochlear and vestibular hair cells, though highly correlated, showed distinct transcriptional signatures. Cochlear hair cells enriched genes including UNC5B and ROBO2, the latter essential for cochlear hair cell innervation, while vestibular hair cells showed enrichment of XIRP2 and GALNTL6, genes also reported in developing mouse cochlear hair cells, suggesting that observed differences may partly reflect spatiotemporal variation in hair cell maturation rather than fully distinct developmental programs. Spiral ganglion-like neurons expressed markers such as PLXDC2, SEMA3A, NTNG1, ZFPM2 and ROR1, whereas vestibular ganglion-like neurons showed enriched expression of PCDH9, TAFA2 and RGS7, consistent with their distinct identities. The mesenchymal compartment revealed otic capsule-like clusters with osteoblast-like gene signatures, otic mesenchyme cell clusters expressing markers such as TBX18, CRYM and the hearing loss-associated genes OTOR, COCH and POU3F4, and shared populations of pericytes, endothelial cells, immune cells, melanocytes and Schwann cells, with melanocytes and endothelial cells increasing over time, consistent with inner ear development.

To validate the atlas, the team generated a separate dataset from a fetal week 12.4 inner ear in which the cochlea and vestibular system were manually separated before nuclei isolation. Jaccard similarity analysis quantified the overlap of gene expression between annotated cell types, and vestibular and cochlear epithelial clusters showed strong concordance. Reference-based mapping of HIEDRA hair cells to the validation dataset confirmed that cochlear hair cells mapped to cochlear hair cells and vestibular hair cells to vestibular hair cells. Cross-species comparisons with publicly available mouse single-cell data from the vestibular crista ampullaris and cochlea reinforced the accuracy of the annotations, and label transfer from a mouse cochlear reference spanning embryonic days 14, 16 and postnatal day 1 increased annotation granularity within the human cochlear epithelium, resolving finer subtypes such as inner and outer pillar cells, Deiters’ cells, inner phalangeal cells, Hensen’s cells and Claudius’ cells.

Beyond descriptive classification, the researchers reconstructed developmental trajectories to infer candidate transcriptional drivers of lineage formation. Applying trajectory inference to cochlear sensory differentiation across pseudotime, they identified three transcriptional states: prosensory, marked by ISL1 and JAG1; sensory, marked by GATA3, CDKN1B, SOX2 and LGR5; and hair cell, marked by INSM1, POU3F4, MYO7A, FGF8 and OTOF. Gene set enrichment analysis along the pseudotime trajectory revealed that PI3K-Akt, ERBB, Wnt, AMPK, Hippo and phospholipase D signaling were active across prosensory and sensory states, while TGF-β and Hippo signaling were suppressed in the hair cell state, indicating that their downregulation may be a necessary step for hair cell fate acquisition. Among the genes nominated by gene regulatory network analysis as candidates connected to the stereocilia program, ANKFN1 emerged as the most robust, showing a significant positive association with a stereocilia gene module score in both cochlear and vestibular hair cells, a finding consistent with the known disruption of Ankfn1 homologs in zebrafish causing vestibular defects.

Mapping disease-associated genes onto HIEDRA cell types revealed selective vulnerabilities. Genes linked to syndromic and nonsyndromic hearing loss, Ménière’s disease, presbycusis, vestibular schwannoma, ototoxicity and tinnitus were cross-referenced with cell populations, and the highest gene burden was observed in the cochlear and vestibular sensory units. However, disorder genes were also highly enriched in the secretory units, which include the cochlear lateral roof cells, vestibular dark cells and melanocytes, cell types that maintain endolymph ionic homeostasis, a critical process for normal inner ear function. The team also identified a potential mechanism linking RIPOR2 mutations, which cause adult-onset hearing loss, to otic mesenchyme cell dysfunction, as RIPOR2 was enriched in both vestibular and cochlear otic mesenchyme subtypes in addition to its known role in stereocilia function. These findings highlight that disorders may arise from dysfunction in both sensory and nonsensory lineages, and that so-called deafness genes may also impact vestibular function.

The most striking mechanistic insight came from the analysis of cochlear lateral roof cells and vestibular dark cells, two poorly characterized secretory populations that regulate potassium homeostasis in the endolymph. Trajectory inference identified early and late transcriptional states in both lineages, and pathway enrichment revealed Wnt, TGF-β and Hedgehog signaling among the pathways enriched in the early state that become less engaged in the late state. Hedgehog signaling stood out because of its central role in early inner ear morphogenesis and its limited prior association with secretory cell specification. Critically, both cell types expressed PTCH1, SMO, KIF7, GLI2 and GLI3 but showed little to no GLI1 expression, which implies the absence of ligand-induced activation, suggesting that repression of Hedgehog signaling may be required for secretory epithelial differentiation.

To test this prediction functionally, the team used human inner ear organoids derived from a GMP-compliant induced pluripotent stem cell line. Previous work had shown that these organoids contain vestibular sensory epithelium but that secretory dark cells do not spontaneously develop. Because sensory and secretory cells develop in parallel in the inner ear, the researchers inhibited Hedgehog signaling with cyclopamine from day 15 to day 30 of organoid differentiation, the window in which vestibular hair cells emerge transcriptionally by day 18 and are detectable by immunohistochemistry by day 30. At day 60, control organoids formed SOX2-positive sensory epithelium but lacked DACH1-positive, OTX2-negative dark cells, whereas cyclopamine-treated organoids developed both SOX2-positive sensory epithelium and DACH1-positive, OTX2-negative vestibular dark cell-like epithelium expressing early ion channel markers including SLC26A4, ATP1B2 and BSND. The treated organoids also showed integration of MLANA-positive melanocytes disrupting the LAM-positive basal membrane, all hallmarks of vestibular secretory function. Single-nucleus RNA sequencing of day 90 cyclopamine-treated organoids confirmed the emergence of dark cell-like populations comprising roughly 22 percent of the otic epithelial cells, compared with roughly 43 percent vestibular supporting cells. These results demonstrate that Hedgehog inhibition is critical for dark cell differentiation in human inner ear organoids, validating the developmental insights from HIEDRA and expanding the model’s capacity to capture the major functional cell types of the human inner ear. The atlas is publicly available through the gEAR portal and the UniApp Dataportal, positioning HIEDRA as both a reference atlas and a mechanistic framework for the developing human inner ear, and illustrating how human developmental atlases can directly inform improved experimental models for mechanistic and translational studies.

Subject of Research: Single-nucleus transcriptomic atlas of human inner ear development

Article Title: A single-nucleus transcriptomic atlas of human inner ear development

Article References: van der Valk, W. H., Udayappan, S. D., van Beelen, E. S. A., Goveia, J., Beatovic, A., Moisse, M., Menafra, R., de Groot, J. C. M. J., Koehler, K. R., van Benthem, P. P. G., & Locher, H. (2026). A single-nucleus transcriptomic atlas of human inner ear development. Nature Neuroscience. https://doi.org/10.1038/s41593-026-02432-8

Image Credits: AI Generated

DOI: 10.1038/s41593-026-02432-8

Keywords: inner ear, single-nucleus RNA sequencing, transcriptomic atlas, Hedgehog signaling, inner ear organoids, hearing loss, vestibular system, gene therapy, cell fate specification, stria vascularis, single-nucleus, transcriptomic

Developmental senescence differs fundamentally from the senescence associated with aging and disease. During embryogenesis, selected cells enter a transient growth-arrested state in restricted tissues at precise developmental stages. Far from being a pathological accident, this programmed arrest appears to serve constructive purposes: senescent cells secrete signaling molecules that influence neighboring tissue, help remodel embryonic structures and are then cleared, often by the embryonic immune system, once their job is done. In this sense, developmental senescence behaves like a morphogenetic regulator—a temporary scaffold that helps shape organs before being dismantled. The authors of the review capture this idea in a central formulation: developmental senescence acts as a morphogenetic regulator whose activity must be tightly integrated with proliferative cues, differentiation programs and tissue-specific signaling networks.

That integration requirement is precisely where things could go wrong. Because the program must operate at the right place, at the right time and at the right intensity, the reviewers reason that any deviation—excessive senescence, insufficient senescence, senescence that lingers too long, or senescence appearing in the wrong tissue—could interfere with normal morphogenesis. A cellular program designed to sculpt tissue could, if misregulated, deform it. This logic transforms developmental senescence from a curiosity of embryology into a plausible contributor to congenital malformations, and it sets the stage for the review’s central proposal: that CHARGE syndrome, with its distinctive constellation of developmental defects, offers an unusually good model in which to investigate that possibility.

CHARGE syndrome is a rare developmental disorder whose name summarizes its most characteristic features: coloboma of the eye, heart defects, choanal atresia (blockage of the nasal passages), growth and developmental delay, genitourinary abnormalities and characteristic ear defects. The clinical picture varies widely between patients, but the underlying genetics is comparatively straightforward. Most individuals with CHARGE syndrome carry pathogenic variants in a single gene, CHD7, which encodes an ATP-dependent chromatin remodeler—a molecular machine that uses the energy of ATP to restructure how DNA is packaged and, in doing so, regulates which genes are accessible for transcription. Chromatin remodelers sit near the top of gene-regulatory hierarchies, which helps explain why mutations in CHD7 can produce effects across so many organ systems at once.

The first pillar of the review’s argument is anatomical. The authors identify a striking three-way overlap between the tissues affected in CHARGE syndrome, the regions where CHD7 is expressed during embryonic development, and the areas where developmental senescence has been observed in experimental studies. This overlapping map includes structures associated with the eye, the inner ear, the pharyngeal regions and the nervous system—the very systems most commonly disturbed in CHARGE patients. The authors are careful to note that such spatial coincidence does not establish causality. Tissues can overlap for many reasons that have nothing to do with a shared mechanism. But the overlap provides something a hypothesis needs before it can be tested: a defined set of tissues in which to look for a functional connection between CHD7 deficiency and altered senescence.

The inner ear supplies the most compelling example in the review. Developmental senescence is known to contribute to the remodeling of the developing inner ear, a structure whose intricate geometry depends on precisely coordinated tissue sculpting. CHARGE syndrome, meanwhile, frequently involves hypoplasia or complete absence of the semicircular canals, the fluid-filled loops of the inner ear that detect rotational movement and are essential for balance. In mouse models, deficiency of Chd7—the mouse counterpart of the human gene—produces major vestibular abnormalities. Putting these observations together, the authors propose that altered senescence-related remodeling could contribute to the characteristic inner-ear defects associated with CHD7 deficiency. If the cellular program that normally refines inner-ear architecture is mis-timed or mis-located in the absence of functional CHD7, the resulting structure could be underdeveloped or absent.

The second pillar is molecular. CHD7 is not an isolated actor; the review documents its intersection with well-known pathways of cell-cycle arrest and senescence, including the p53 and p21 pathways and TGFβ-related signaling. These pathways form the canonical machinery that cells use to halt division and enter a senescent state. The experimental evidence connecting them to CHD7 is particularly intriguing. In zebrafish embryos, reduced chd7 expression causes cell-cycle arrest alongside increased expression of several cell-cycle inhibitors—the molecular fingerprint of cells being pushed toward arrest. In mouse models, inappropriate activation of p53 can produce major CHARGE-like abnormalities on its own, and, more strikingly, partially reducing the dose of Trp53, the gene encoding p53, can rescue several of the developmental defects caused by Chd7 deficiency. That rescue experiment suggests the two pathways are not merely parallel but functionally entangled: dialing down one can compensate for the loss of the other.

Evidence from other developmental models reinforces the broader principle that senescence must be precisely controlled during embryogenesis. Abnormal senescence has been implicated experimentally in models involving Six1 deficiency, exposure to the drug valproic acid, maternal diabetes and trisomy 21. In each of these contexts, developmental abnormalities appear to arise when senescence occurs in the wrong location, at the wrong time or at an inappropriate level. The review extends this logic to a wider set of congenital conditions, considering whether senescence-related mechanisms might contribute to Rett syndrome, Treacher-Collins syndrome, 22q11.2 deletion syndrome, Waardenburg syndrome and related SOX10-associated disorders, and Kallmann syndrome. Here the authors urge restraint: the evidence varies considerably among these disorders, and it remains unresolved whether the cellular changes observed in them represent authentic developmental senescence or related but distinct cell-arrest states.

The authors themselves are explicit that the connection between CHD7 and developmental senescence remains a working hypothesis. As they state, the available anatomical, developmental and molecular evidence does not yet demonstrate that CHARGE syndrome is a disorder of senescence misregulation. The evidence is heterogeneous and often indirect, assembled from different organisms, different tissues and different experimental systems. What is needed now are direct experiments: mapping senescence markers across CHD7-sensitive embryonic tissues to see whether the spatial and temporal patterns of senescence are actually disturbed when CHD7 is lost, and determining how CHD7 affects chromatin accessibility, cell-cycle control and senescence-associated signaling at the molecular level. Chromatin profiling of CHD7-deficient embryonic cells, combined with single-cell analysis of senescence markers, could reveal whether the chromatin remodeler directly regulates the genetic programs that initiate or maintain developmental senescence.

There is also a therapeutic dimension, approached with appropriate caution. Senescence-modulating approaches—drugs that clear senescent cells or suppress their secretory activity—have shown benefits in some experimental models of developmental defects. But the authors emphasize that developmental senescence is itself a normal and beneficial component of morphogenesis. Bluntly suppressing it during embryogenesis could cause as much harm as the misregulation it aims to correct. Any future intervention would need to be exquisitely targeted in time, tissue and mechanism. For now, the value of the review lies in its framing: it presents CHARGE syndrome as a candidate model for understanding how the misregulation of a normally constructive developmental program could contribute to congenital disease, linking CHD7-dependent chromatin regulation to senescence pathways and embryonic tissue remodeling. Establishing a causal role will require direct functional evidence, particularly in the CHD7-sensitive structures such as the inner ear where the anatomical, developmental and molecular threads of the hypothesis converge most tightly. If those experiments succeed, they would not only illuminate a rare syndrome but also deepen understanding of how embryos use a program usually associated with aging to build new bodies.

Subject of Research: The role of developmental senescence misregulation as a candidate mechanism in CHARGE syndrome

Article Title: Developmental senescence emerges as a candidate mechanism in CHARGE syndrome

Article References: Developmental senescence emerges as a candidate mechanism in CHARGE syndrome. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: developmental senescence, CHARGE syndrome, CHD7, chromatin remodeling, morphogenesis, p53, p21, TGFβ signaling, inner ear, congenital disorders, cell-cycle arrest, embryonic development