Viral Barcodes Reveal the Hidden Family Tree of the Newborn Mouse Brain

Every mammalian brain begins as a modest pool of progenitor cells, yet it ends up containing hundreds of molecularly distinct cell types. How that transformation unfolds—who descends from whom, and where each descendant ultimately settles—has remained one of developmental neuroscience’s most stubborn questions. Now, a team led by Guohua Yuan and Tomasz Nowakowski at the University of California, San Francisco, together with colleagues at the Allen Institute for Brain Science, has produced the most comprehensive lineage map to date of the newborn mouse forebrain. Writing in Nature, the researchers describe an atlas of clonal relationships spanning the cortex, hippocampus, striatum, thalamus and olfactory bulb, revealing a striking developmental logic: some cell families stay rooted in the neighborhoods where they were born, while others scatter across the entire brain.

The technical centerpiece of the study is a method the team calls STICR, a lentiviral barcoding system that stamps progenitor cells with unique heritable DNA sequences. When a barcoded progenitor divides, all of its descendants carry the same genetic tag, allowing researchers to reconstruct family trees long after development has moved on. By injecting the virus at a series of embryonic and postnatal timepoints—from embryonic day 11 through postnatal day 0—and collecting tissue at postnatal day 4, the team captured clones born during distinct developmental windows. Each labeled cell was then profiled with single-cell RNA sequencing, and its barcode was read out alongside its transcriptome, linking identity to ancestry in a single measurement.

Knowing what a cell is, however, is only half the story; knowing where it sits is equally important. To anchor their lineage data in anatomy, the researchers used MERFISH, a spatial transcriptomics method that maps thousands of genes across intact coronal sections of the forebrain. By registering the cellular profiles recovered from dissociated tissue onto these spatial maps, the team could ask not only which cell types share a common ancestor, but also how far those relatives traveled from one another. The result is a spatiotemporal clonal atlas: a record of lineage, identity and location woven together across the entire newborn forebrain rather than a single privileged region such as the cortex, which has dominated most prior lineage studies.

The scale of the dataset allowed the authors to run careful computational checks on their inferences. Because viral labeling captures only a fraction of cells, the team built simulation frameworks using ground-truth clones to model how partial sampling affects the recovery of lineage structure. These simulations, described in the paper’s extended data, quantified how many multicellular clones are needed to reliably detect the constituent cell types of a lineage and how often apparent fate biases could arise by chance. Such validation matters, because the study’s headline conclusions rest on statistical patterns of clone sharing between cell types rather than on direct observation of dividing cells.

Among the most consequential findings is a new view of the striatum, the brain’s major input hub for movement and reward. The atlas reveals previously unrecognized differences in how ventral and dorsal medium spiny neurons—the principal projection neurons of the striatum—are generated. It also uncovers lineage relationships that had gone unexplored: late-born medium spiny neurons share clonal ancestry with striatal astrocytes and with distinct subpopulations of olfactory bulb neurons. This connects the striatum’s developmental program to the continuous postnatal production of neurons that migrate into the olfactory bulb, a hallmark of the subventricular zone that has long fascinated neuroscientists studying adult neurogenesis.

The broader principle that emerges from the atlas is a tale of two lineages. Glutamatergic neurons—the forebrain’s excitatory workhorses—and astrocytes, the star-shaped glial cells that support synapses, are clonally related to one another and remain within their region of origin. A clone born in the cortex stays in the cortex; one born in the hippocampus stays in the hippocampus. GABAergic neurons, the inhibitory counterpart, follow a different rule. They are clonally linked to oligodendrocyte precursor cells, the myelin-forming lineage, and they disperse extensively, crossing regional and structural boundaries. The findings echo and extend earlier work showing that clonally related interneurons spread widely across the forebrain, but the new atlas places that dispersal within a whole-brain framework and ties it to glial fate.

That dispersal carries a provocative clinical hint. The researchers found that clones of GABAergic neurons with broad regional dispersion are enriched for genes implicated in neurodevelopmental disorders, including genes associated with autism. In other words, the cell lineages most likely to spread across the brain are also the ones whose genetic programs intersect most heavily with disease risk. This observation suggests that disruptions to widely dispersing inhibitory lineages could have consequences distributed across multiple brain regions, offering a potential developmental framework for understanding why genetic risk factors for neurodevelopmental conditions produce such varied and widespread effects.

The temporal dimension of the atlas adds further texture. By comparing clones labeled at different embryonic and postnatal stages, the team traced how lineage composition shifts over time: early-labeled clones are dominated by deep-layer cortical neurons, while later windows capture upper-layer neurons, glia and the postnatally generated populations destined for the olfactory bulb. In the olfactory bulb itself, the data distinguish embryonically or locally generated GABAergic neurons from postnatally born neurons still migrating through the rostral migratory stream at the time of collection. Cajal–Retzius cells, the pioneer neurons that guide cortical layering, also appear in the atlas with their own regionally specific lineage relationships to astrocytes and ependymal cells.

Methodologically, the study demonstrates how viral barcoding, single-cell transcriptomics and spatial transcriptomics can be fused into a single coherent picture of organ-scale development. The authors have made their resources broadly available: the single-cell and barcode datasets are deposited in the Gene Expression Omnibus under accession GSE341480, an interactive browser of the single-cell and MERFISH data is hosted through the UCSC cell browser, the image dataset is available through the Brain Image Library, and the custom analysis code is published on GitHub. For a field increasingly reliant on large-scale atlases, this openness means other laboratories can immediately interrogate the lineage relationships, test alternative hypotheses and integrate the data with their own developmental and disease-focused studies.

The implications reach well beyond the mouse. Human studies have suggested that individual cortical progenitors can produce both excitatory and inhibitory neurons, and the new mouse atlas provides a mechanistic reference against which human lineage data can be interpreted. By establishing that lineage fate—whether a progenitor’s descendants become neurons, astrocytes or oligodendrocyte precursor cells—is governed by regionally specific rules that differ fundamentally between excitatory and inhibitory lineages, the work offers a foundational framework for dissecting how the mammalian forebrain is assembled, and how that assembly goes awry in disease. As the authors note, the atlas is intended as a reference point for the field: a first whole-forebrain census of who is related to whom, where they ended up, and when they were born.

Subject of Research: Clonal lineage relationships and cell fate specification during mouse forebrain development

Article Title: Spatiotemporal clonal architecture of the newborn mouse forebrain

Article References: Yuan, G., Kunst, M., Steyert, M. R., Keefe, M. G., Mathieu, R., van Velthoven, C. T. J., McMillen, D., Waters, J., Fukushima, Y., Kazerounian, A., Alvarez-Buylla, A., Zeng, H., & Nowakowski, T. J. (2026). Spatiotemporal clonal architecture of the newborn mouse forebrain. Nature. https://doi.org/10.1038/s41586-026-11064-8

Image Credits: AI Generated

DOI: 10.1038/s41586-026-11064-8

Keywords: mouse forebrain, clonal lineage, lentiviral barcoding, spatial transcriptomics, MERFISH, single-cell RNA sequencing, GABAergic neurons, glutamatergic neurons, astrocytes, oligodendrocyte precursor cells, neurodevelopmental disorders, striatum