Common marmosets are small New World monkeys native to South America. Their relatively close evolutionary relationship to humans, compact size, and susceptibility to age-related memory decline have made them increasingly valuable in biomedical research. Unlike mice, marmosets share more aspects of primate biology with humans, including features of brain development, aging, immune function, and social behavior. Yet researchers have been working with an incomplete genetic map. The first marmoset reference genome, released in 2014, contained gaps, inaccuracies, and unresolved repetitive sequences that limited the ability to detect important genetic differences between animals.

A reference genome is a standardized representation of a species’ DNA against which individual genomes can be compared. When the reference is incomplete, genetic variants may be missed or incorrectly classified, particularly in repetitive and structurally complex regions. The new sequence applies the Telomere-to-Telomere approach, which aims to reconstruct chromosomes continuously from one end, or telomere, to the other. Advances in long-read DNA sequencing, highly accurate sequencing technologies, and computational assembly algorithms allowed the researchers to resolve regions that conventional methods had previously left fragmented or ambiguous.

“Routine T2T genomics is making findings easier and more plausible, as we’re able to much more easily access these complex regions,” said Prajna Hebbar, a UC Santa Cruz Biomolecular Engineering and Bioinformatics Ph.D. student who led the effort with Professor Benedict Paten. The new marmoset genome is part of a broader wave of Telomere-to-Telomere studies demonstrating that complete genome assembly is becoming practical across species, rather than remaining a landmark achievement limited to humans. The consortium produced the first complete human genome sequence in 2022.

Using the new reference, the team examined genetic variation across 230 marmosets. The analysis found differences in numerous genes associated with Alzheimer’s disease in humans, as well as genes involved in immune defense. The researchers also focused on a set of genes linked to Alzheimer’s, Parkinson’s disease, and related neurodegenerative conditions. They generated high-quality reference sequences for 76 corresponding marmoset gene copies, giving researchers a more reliable foundation for studying how specific variants influence brain health and disease risk.

The genome also revealed previously undescribed forms of several genes when the researchers combined the reference sequence with transcriptomic data. Transcriptomics measures RNA molecules produced by cells and tissues, offering a snapshot of which genes are active and which are silent. Among the genes showing newly identified forms was PSEN1, a gene whose mutations are the most frequent known cause of early-onset familial Alzheimer’s disease. The discovery does not yet establish whether the newly observed forms alter disease susceptibility or progression, but it opens a path for experiments that would have been difficult or impossible with the older reference genome.

Another major result concerns the Major Histocompatibility Complex, or MHC, a dense group of genes that helps the immune system distinguish the body’s own cells from foreign organisms. Variation within the MHC influences susceptibility to autoimmune diseases such as type 1 diabetes, multiple sclerosis, and rheumatoid arthritis, as well as responses to infection and transplantation. The researchers produced a complete record of the marmoset MHC region and annotated several complex genes that had not previously been catalogued. This information could improve the design and interpretation of studies using marmosets to investigate immune-related disease.

The complete sequence further uncovered unusual patterns in ribosomal DNA, or rDNA. These repeated DNA arrays encode essential components of ribosomes, the molecular machines that build proteins. In marmosets, entire rDNA arrays appear to move between chromosomes more freely than expected, with individual chromosomes gaining or losing copies. The researchers also detected differences between males and females in the distribution of these sequences, a pattern previously reported in orangutans and gibbons. Because ribosomal DNA is central to cellular protein production, these findings may offer new clues about chromosome organization and genome stability.

The study also provides a clearer view of centromeres, specialized chromosome regions required for accurate chromosome separation during cell division. Centromeres are often composed of highly repetitive DNA and have historically been among the most difficult portions of genomes to assemble. Their structure can affect chromosome behavior, fertility, development, and disease. By resolving these regions in the marmoset, the new reference gives researchers an opportunity to investigate how primate chromosomes are maintained and how genomic changes accumulate over evolutionary time.

The researchers say the resource will allow scientists to move beyond technical limitations and examine the biology of complex genomic regions directly. The work was conducted by collaborators from UC Santa Cruz, the Jackson Laboratory, the University of Pittsburgh, the University of Washington, Oregon Health & Science University, the Stowers Institute for Medical Research, and the German Primate Center, with support from the U.S. National Institutes of Health. As complete genome sequencing becomes faster and less expensive, the same methods could eventually support personalized genomics, in which an individual’s fully resolved genome serves as the reference for medical care. For now, the marmoset genome offers researchers a substantially more accurate foundation for studying primate evolution, immune biology, aging, and neurodegenerative disease.

Subject of Research: The complete genome sequence of the common marmoset and its applications in disease research, comparative genomics, and primate biology.

Article Title: A Complete Genome for the Common Marmoset

News Publication Date: 6-Aug-2026

Web References: https://doi.org/10.1016/j.cell.2026.07.017

References: Cell, DOI: 10.1016/j.cell.2026.07.017

Image Credits: Carolyn Lagattuta/UC Santa Cruz

Keywords: common marmoset, complete genome, Telomere-to-Telomere, genomics, Alzheimer’s disease, neurodegeneration, MHC, ribosomal DNA, centromeres, primate research, personalized genomics

At the core of this revolutionary analysis is the discovery of aggressive endometrial cancer in two elderly female lemurs, L2 and L3. This malignancy, the most common cancer of the female reproductive tract in women and a leading cause of cancer-related mortality, has rarely been modeled naturally in laboratory animals. Unlike traditional rodent models which predominantly emulate low-grade tumors, the lemur’s cancer cells exhibit molecular signatures strongly resembling high-grade, metastatic human type 2 endometrial carcinoma, presenting a crucial new avenue for studying this intractable form of cancer.

Strikingly, one of the lemurs’ metastatic tumors was found in the lung, expressing significant levels of the oxytocin receptor gene (OXTR), which is characteristically enriched in female reproductive tissues. Integration with the organism-wide atlas confirmed the tumor’s uterine origin, while histopathological examinations verified metastases not only in the lungs but also in mesenteric lymph nodes. This cellular evidence underscores the utility of organism-wide atlases to pinpoint primary tumor sites in cancers of unknown origin—a clinical challenge affecting around 2% of human cancer cases.

At the molecular level, the uterine tumorous cells demonstrated enriched expression of canonical markers including CA125 (MUC16) and HE4 (WFDC2), widely recognized as serum biomarkers for human endometrial and ovarian cancers. Moreover, genes frequently implicated in aggressive endometrial tumorigenesis such as MYC, ERBB2 (HER2), and INHBB were upregulated, collectively mirroring the molecular profile of human type 2 tumors. The metastatic lung lesions exhibited continued expression of ERBB2 and its functional partners EGFR and EGF, suggestive of autocrine growth signaling, while simultaneously downregulating estrogen receptor (ESR1), a hallmark of advanced disease progression in humans.

Beyond oncological insights, the atlas reveals surprising aspects of lemur adipose physiology that challenge established paradigms. Mouse lemurs undergo pronounced seasonal metabolic shifts akin to hibernation states in other mammals. By profiling adipocytes across four distinct fat depots, researchers identified two main adipocyte populations differentiated by their expression of UCP1, a protein pivotal in non-shivering thermogenesis. These populations span from UCP1-high “brown-like” adipocytes characterized by enriched thermogenic regulators, to UCP1-low “white-like” adipocytes with elevated expression of classical white fat markers, blurring the conventional white-brown adipose tissue dichotomy.

Equally intriguing is the unusually low expression of leptin (LEP) in lemur adipocytes—a stark contrast to its prominent presence in human and mouse fat cells, where it modulates appetite and energy expenditure. Despite minimal leptin transcript levels, its receptor LEPR remains selectively and robustly expressed. This atypical pattern raises the possibility of highly context-dependent leptin expression or alternative regulatory mechanisms superseding canonical leptin function, potentially reflecting adaptations linked to the species’ unique seasonal physiology.

Further complicating the white-brown adipocyte distinction, both CIDEA, a prototypical brown fat marker, and RBP4, a key adipokine associated with white adipocytes, are uniformly expressed across the entire adipocyte landscape. This molecular continuum could indicate a flexible interconversion mechanism, allowing lemurs to dynamically modulate energy storage and thermogenesis in response to environmental demands, thus supporting their seasonal cycles of body weight, temperature, and metabolic rate.

Notably, no fat depot was composed solely of brown-like adipocytes; rather, each depot contained a mix or exclusively white-like cells. Gonadal fat depots displayed an enriched inflammatory gene signature, including S100A family proteins and interleukins linked to insulin resistance and metabolic stress, suggesting depot-specific immune-adipocyte interactions that could influence metabolic health especially during seasonal transitions.

The utility of the mouse lemur as a model organism expands beyond basic biology into translational research, particularly for cancers like high-grade endometrial carcinoma that lack robust animal models. Given the molecular parallels between lemur and human tumors, including shared expression of targets responsive to anti-angiogenic, anti-EGFR, and endocrine therapies, the lemur offers an invaluable in vivo system that could accelerate the development and testing of novel treatments.

Moreover, the described cellular complexity of adipose tissues provides fertile ground for probing mechanisms governing seasonal metabolic regulation in primates. Understanding adipocyte plasticity and the regulation of thermogenic programs in a natural seasonal context may illuminate strategies to tackle human metabolic disorders such as obesity and diabetes.

This comprehensive organism-wide single-cell atlas thus bridges a crucial gap between primate biology and human medicine. It not only reveals previously underappreciated physiological idiosyncrasies of a small primate but also pioneers experimental avenues to dissect disease processes in a model more closely aligned with humans than rodents.

Future work will hinge on experimental validation of these observations. Confirming the tumorigenic potential of described cell populations, dissecting the seasonal cues modulating leptin expression, and characterizing adipose tissue remodeling across seasons are essential steps toward unlocking the full research potential of Microcebus murinus.

In a broader context, this study exemplifies the power of integrative single-cell analysis to decode complex physiological and pathological states across entire organisms. It underscores how high-resolution cellular maps can identify disease origins, elucidate cell type-specific expression programs, and reveal tissue-specific adaptations with unprecedented clarity.

As the field moves forward, the mouse lemur cell atlas sets a new standard for organismal biology and primate research. It invites a reevaluation of established biological dichotomies, such as the white versus brown adipocyte classification, and opens promising investigative pathways into primate-specific disease mechanisms and therapeutic responses.

The implications extend well beyond mouse lemurs, contributing fundamentally to our understanding of evolutionary conservation and divergence in mammalian tissue organization, disease susceptibility, and physiological adaptation. The atlas thus not only enriches the scientific toolbox but also holds the promise of accelerating translational advances in human health.

Subject of Research: Mouse lemur cellular atlas; primate disease and physiology; endometrial cancer; adipose tissue biology

Article Title: Mouse lemur cell atlas informs primate genes, physiology and disease

Article References:
Ezran, C., Liu, S., Chang, S. et al. Mouse lemur cell atlas informs primate genes, physiology and disease. Nature (2025). https://doi.org/10.1038/s41586-025-09114-8

Image Credits: AI Generated