When the surrounding water dilutes, a shrimp’s cells face a triple assault. Osmotic stress makes cells swell as water rushes in, disrupting the delicate water balance inside tissues. Ionic stress impairs the channels and enzymes that keep sodium, potassium and chloride in check. And oxidative stress generates reactive oxygen species that oxidize proteins, inactivate enzymes and damage DNA. Together, these pressures can trigger apoptosis, alter membrane fluidity and ultimately kill the animal. Understanding how shrimp blunt this cascade is not just an academic exercise; it directly determines survival, growth and productivity on farms that supply a large share of the world’s seafood protein.

The review’s first major theme is how shrimp perceive salinity change in the first place. G protein-coupled receptors, or GPCRs, are abundant in penaeid genomes: the L. vannamei reference genome contains 457 GPCR genes, and transcriptome curation in P. monodon identified three major classes totaling 350 members. Intriguingly, the authors caution that direct evidence for GPCRs acting as primary salinity sensors remains limited. Instead, these receptors are more plausibly engaged indirectly, as salinity shifts alter the availability of neuroendocrine and paracrine ligands. Once activated, GPCRs funnel signals through cAMP, protein kinase A, PI3K-Akt and MAPK cascades. Transcriptomic profiling of P. monodon gills under chronic low salinity showed differentially expressed genes mapping to PI3K-Akt, MAPK and calcium signaling pathways, supporting a role for GPCR-linked cascades in gill-centered osmoregulatory acclimation.

Calcium signaling emerges as a second, faster perception module. As extracellular osmotic pressure drops, calcium-permeable membrane channels open and calcium is also mobilized from intracellular stores such as the endoplasmic reticulum, producing a transient spike in cytosolic calcium. In P. monodon, acute low-salt stress significantly enriches gene sets for calcium ion transmembrane transport, calmodulin binding and regulation of cytosolic calcium concentration, accompanied by increased activity of Ca2+/Mg2+-ATPase. The calcium wave activates a battery of calcium-sensitive kinases and phosphatases that fine-tune ion pumps through phosphorylation, restoring not only calcium balance but also sodium and potassium equilibrium. Strikingly, the cellular energy sensor AMPK rides along: hepatopancreatic AMPK-alpha transcripts increase roughly 28-fold just six hours after Pacific white shrimp are transferred from salinity 20 to salinity 3, linking osmotic calcium dynamics to metabolic reprogramming through calcium/calmodulin-dependent kinase kinase pathways.

The third perception layer is phospholipid signaling and membrane remodeling. Low salinity directly changes the physical state of cell membranes, particularly their fluidity and the activity of embedded proteins. Shrimp respond by adjusting membrane phospholipid composition, and over longer exposures they shift the ratio of saturated to unsaturated fatty acids to keep membranes supple. Phospholipase C-mediated hydrolysis of phosphoinositides generates second messengers such as IP3 and diacylglycerol, tuning membrane-protein interactions and the trafficking of ion-transport systems. The review frames this lipid turnover primarily as membrane remodeling that stabilizes integrity and preserves the function of osmoregulatory channels and pumps during cell swelling and volume recovery, a subtle but crucial distinction for interpreting the data.

Downstream of perception, three kinase networks translate stress signals into coordinated action. The MAPK pathway, with its ERK, JNK and p38 branches, governs cell growth, stress-responsive transcription and apoptosis; ERK supports proliferation while JNK and p38 can eliminate severely damaged cells and regulate inflammatory gene expression. The PI3K-Akt pathway acts as a survival engine: activated PI3K generates PIP3, which engages Akt, which in turn phosphorylates mTOR to promote anabolic metabolism while suppressing apoptotic proteins such as Bad and excluding FOXO transcription factors from the nucleus. Negative feedback through PTEN keeps the pathway from pathological overactivation. Meanwhile, the NF-kappaB pathway, engaged via I-kappa-B regulation and nuclear translocation, promotes immune, stress-response and anti-apoptotic gene programs. Together these modules drive gill-centered osmoregulation, immune priming and antioxidant control.

At the organ level, the gills take center stage. Gill ionocytes dynamically adjust ion absorption or excretion through core transport systems, most notably Na+/K+-ATPase and carbonic anhydrase. In dilute water, P. monodon ramps up ion uptake to raise internal osmotic pressure and prevent excessive water influx and cellular rupture. Na+/K+-ATPase burns ATP to exchange three sodium ions for two potassium ions across the membrane, maintaining the electrochemical gradient, and its activity typically rises under low salinity. Carbonic anhydrase catalyzes the reversible hydration of carbon dioxide, producing bicarbonate and protons that support the Na+/H+ exchanger and acid-base balance. Recent transcriptome work in P. monodon found markedly upregulated Na+/K+-ATPase subunits and elevated carbonic anhydrase transcripts under low salinity, alongside dynamic changes in actin and tubulin genes indicating cytoskeletal remodeling of gill epithelia. Antennal and maxillary glands contribute auxiliary water and ion excretion, though shrimp-specific mechanistic data for the latter remain thin.

The review also highlights two cellular quality-control systems that have received less attention. Autophagy, the degradation and recycling of damaged proteins and organelles, is initiated when energy stress activates AMPK and relieves mTOR-mediated inhibition of the Atg1 initiation complex. A cascade of Atg proteins, including the transmembrane Atg9 and the Atg7-Atg3 conjugation machinery that lipidates Atg8, builds autophagosomes that fuse with lysosomes to recycle cellular debris. In parallel, endoplasmic reticulum stress engages three sensor arms: PERK slows protein synthesis by phosphorylating eIF2-alpha while activating ATF4; ATF6 is cleaved in the Golgi to activate ER quality-control genes; and IRE1 splices XBP1 mRNA to boost chaperone and lipid biosynthesis. Proteins such as GRP78/BiP and CHOP decide whether the cell restores folding capacity or succumbs to apoptosis.

Salinity stress also reshapes immunity and redox balance. Under hyposalinity, shrimp upregulate scleroproteins that thicken the cuticle, lysozymes that dissolve bacterial cell walls, and antilipopolysaccharide factors that neutralize bacterial endotoxin. Recent transcriptomic data from P. monodon show that low salinity alone triggers upregulation of Toll-like receptor genes and downstream NF-kappaB components, suggesting osmotic stress primes innate immunity even without pathogens. Because immune effector processes and osmotic disturbance both elevate reactive oxygen species, antioxidant defense is tightly coupled to immune function. The Keap1-Nrf2 axis sits at the center: oxidative stress releases Nrf2 from Keap1, allowing it to enter the nucleus and bind antioxidant response elements, switching on superoxide dismutase, catalase, glutathione peroxidase and heme oxygenase-1, with feedback mechanisms preventing an overactive response.

The practical payoff is already visible in feeding trials. The review compiles nutritional interventions with direct experimental support for improved low-salinity resilience: cholesterol and phospholipids to stabilize membranes, vitamin C derivatives such as L-ascorbyl-2-polyphosphate to buffer oxidation, potassium and magnesium supplementation to enhance ion balance, and myo-inositol to support stress tolerance. Looking forward, the authors argue that identifying the true upstream osmosensors, integrating multi-omics with time-series designs, and exploiting chromosome-level genomes of L. vannamei, P. monodon and Marsupenaeus japonicus for comparative genomics and marker-assisted breeding will be essential. Genome editing remains technically difficult in crustaceans, so selective breeding and genomic selection carry near-term weight. As salinity fluctuations grow more frequent and less predictable, decoding the shrimp’s molecular playbook may prove decisive for building climate-resilient aquaculture systems.

Subject of Research: Molecular and physiological adaptations of penaeid shrimp to low-salinity stress

Article Title: Molecular and physiological adaptations to low-salinity stress in penaeid shrimp: a focus on Litopenaeus vannamei and Penaeus monodon

Article References: Huang, S., Zhou, F., Jiang, S., Li, E., & Li, Y. (2026). Molecular and physiological adaptations to low-salinity stress in penaeid shrimp: a focus on Litopenaeus vannamei and Penaeus monodon. Stress Biology, 6(1), Article 34. https://doi.org/10.1007/s44154-026-00295-4

Image Credits: AI Generated

DOI: 10.1007/s44154-026-00295-4

Keywords: penaeid shrimp, Litopenaeus vannamei, Penaeus monodon, low-salinity stress, osmoregulation, GPCR signaling, calcium signaling, Na+/K+-ATPase, autophagy, endoplasmic reticulum stress, Nrf2 antioxidant pathway, aquaculture

The research team, led by Laís Teixeira Bonfim and Edivaldo Herculano Corrêa de Oliveira, working at the Federal University of Pará and the Evandro Chagas Institute, exposed two rat cell lines to methylmercury for 24 hours. The B103 neuroblastoma line served as a stand-in for neurons, while the C6 glioma line represented glial cells, the support cells that outnumber neurons in the brain. Crucially, the researchers chose concentrations anchored to previously determined LC50 values, the doses that kill half the cells. For neurons, they tested 0.1 micromolar, a low non-lethal dose, and 2.8 micromolar. For glial cells, they used the same low dose alongside 6.3 micromolar. RNA was then extracted and hybridized to Agilent microarrays capable of interrogating more than 44,000 gene transcripts simultaneously, with all experiments performed in triplicate and quality-controlled through principal component analysis and correlation metrics.

The results in neuronal cells defied a simple dose-response logic. At the low 0.1 micromolar concentration, 798 genes shifted their expression, with 644 upregulated and 154 downregulated. Yet at the higher 2.8 micromolar dose, the number of differentially expressed genes actually fell to 572. The authors suggest this inversion may reflect a hormesis effect, a biological phenomenon in which low doses of a stressor provoke defensive signaling while high doses suppress the transcriptional machinery altogether. Seven genes changed more than threefold at the low dose, including Dcx, a marker of migrating neurons, and Trim14, while five genes crossed that threshold at the high dose. Only five overlapping genes appeared in both treatments, and they share a common thread: they participate in building glycosylphosphatidylinositol-anchored proteins, or GPI-APs, molecules that tether signaling proteins to the cell membrane and are essential for adhesion, migration, and immune responses. This is the first evidence that methylmercury disrupts GPI-anchored protein biology, opening a fresh window on how the toxin may sabotage membrane organization and signal transduction.

Functional annotation of the neuronal response revealed further surprises. At the low dose, differentially expressed genes were enriched for steroid dehydrogenase activity, specifically the enzyme 3β-hydroxysteroid dehydrogenase, which converts pregnenolone to progesterone and dehydroepiandrosterone to androstenedione in the brain. These neurosteroids are critical for neurodevelopment and neuroprotection, and the authors propose that methylmercury’s well-documented mitochondrial damage could starve this pathway of substrate, while oxidative stress disrupts the ERK/MAPK signaling that regulates the enzyme’s expression. No prior study had reported effects of methylmercury on 3β-HSD in the brain. The serotonin receptor pathway also emerged as a target, consistent with evidence that methylmercury disrupts neurotransmitter regulation and that mercury compounds reduce serotonin binding to its receptors in vitro.

At the higher neuronal dose, the picture shifted toward ion transport. Genes involved in transporter activity, particularly metal ion transport, dominated the enrichment analysis, alongside terms for ion channel complexes, neurogenesis, and nervous system development. Reactome pathway analysis confirmed that solute carrier proteins, or SLCs, were heavily implicated. These membrane transporters act as sentinels at the blood-brain barrier and maintain homeostasis within neurons and glia. Their disruption could allow metal ions to accumulate inside cells, generating oxidative stress and cascading damage to gene expression, protein synthesis, and enzyme activity. Studies in zebrafish and Nile tilapia have shown that mercury induces similar transporter upregulation in aquatic organisms, suggesting an evolutionarily conserved vulnerability.

The glial cells told a different story. At 0.1 micromolar, 812 genes changed expression, with a striking bias toward downregulation: 612 genes were suppressed against only 200 upregulated. The most prominent pathway affected was Rho-GTPase signaling, a molecular network that governs the actin cytoskeleton and cell morphology. This finding dovetails with prior work showing that methylmercury activates RhoA in astrocytes, causing process retraction and loss of the contact guidance that astrocytes provide to growing axons. At the high 6.3 micromolar dose, 872 genes shifted, and the analysis converged on a single critical molecular function: ATPase activity, specifically the sodium-potassium-exchange-ATPase. This pump is the workhorse of neuronal energy metabolism, maintaining the ion gradients that underpin every action potential. Its inhibition by methylmercury has been linked to oxidative stress, impaired neurotransmitter uptake of dopamine and glutamate, and even teratogenesis.

Perhaps the most compelling thread running through both cell types was the role of microRNAs, the short regulatory RNAs that fine-tune gene expression after transcription. Using the miRTarBase database of experimentally validated microRNA-target interactions, the researchers predicted which microRNAs regulate the differentially expressed genes. In neuronal cells, 23 microRNAs targeted 162 genes at the low dose and 14 targeted 97 genes at the high dose. In glial cells, 23 microRNAs regulated 314 genes at the low dose and 24 regulated 337 at the high dose. When these microRNAs were mapped onto KEGG signaling pathways, one target emerged above all others: the mitogen-activated protein kinase, or MAPK, pathway, which was impaired by methylmercury in both cell lines regardless of dose. The MAPK cascade, encompassing the p38, ERK, and JNK subfamilies, orchestrates cellular responses to stress, proliferation, and apoptosis, and methylmercury is known to hijack it to promote oxidative damage and inflammation.

A specific microRNA family, mmu-miR-466, appeared consistently across conditions, regulating more than ten signaling pathways including unsaturated fatty acid biosynthesis, GABAergic synapse function, and calcium signaling. This finding resonates with decades-old observations that developmental methylmercury exposure disrupts the fatty acid composition of myelin cerebrosides, and with more recent work in migratory birds showing that mercury perturbs lipid metabolism with consequences for flight performance. In glial cells at the high dose, three additional microRNAs, mmu-miR-1192, mmu-miR-495-3p, and mmu-miR-669c-3p, collectively regulated roughly 40 pathways, with axon guidance emerging as the most significant. Within that pathway, the microRNAs targeted receptors in the WNT signaling cascade, which directs growing axons toward their destinations during development.

To connect these molecular perturbations to human disease, the team performed Human Phenotype Ontology enrichment analysis, asking whether the altered genes correlated with documented clinical phenotypes. The results were sobering. Across both cell lines and all doses, the most enriched terms related to abnormalities of the nervous system, skeletal muscle, brain morphology, and higher mental functions. The low-dose glial exposure specifically flagged hypotonia, low intelligence quotient, and aplasia or hypoplasia of the central nervous system, while the high dose pointed to neurodevelopmental delays and disorders of brain morphology. These computational predictions align with the historical record, from the 1971-1972 Iraq poisoning epidemic, which established the exquisite vulnerability of the developing fetus, to modern dose-response analyses showing harm at even low prenatal exposures.

The study’s significance extends beyond the laboratory. Methylmercury enters the food web through microbial methylation of inorganic mercury in aquatic environments, a process amplified by artisanal gold mining, industrial wastewater, and agricultural runoff. Because it crosses both the blood-brain barrier and the placenta, contaminated fish and seafood remain the primary route of human poisoning, with consequences ranging from cerebellar ataxia and tremors to memory loss and impaired cognition. By demonstrating that non-lethal concentrations rewire gene expression in ways that map directly onto neurological disease phenotypes, this work strengthens the scientific case for stringent environmental regulation and public health protections, particularly for pregnant women and young children. It also hands toxicologists a new set of molecular markers, from GPI-anchored protein synthesis to the mmu-miR-466 family, that could serve as early-warning signals of neurotoxicity long before cell death begins.

Subject of Research: Transcriptomic effects of methylmercury exposure on rat neuronal and glial central nervous system cell lines

Article Title: Effects of methylmercury exposure on the transcriptomes of cell lines from the rat central nervous system

Article References: Bonfim, L. T., Amorim, C. K. N., de Oliveira, E. H. C., & Ferreira, W. A. S. (2025). Effects of methylmercury exposure on the transcriptomes of cell lines from the rat central nervous system. Discover Toxicology, 2(1), Article 25. https://doi.org/10.1007/s44339-025-00032-y

Image Credits: AI Generated

DOI: 10.1007/s44339-025-00032-y

Keywords: methylmercury, neurotoxicity, transcriptome, microRNA, glial cells, neurons, MAPK signaling, Na+/K+-ATPase, GPI-anchored proteins, oxidative stress, blood-brain barrier, neurodevelopment