Finally, this work was supported by the NIH BICCN, Nomis Foundation, @jcchildsfund.bsky.social, @hhmi.org, and others. Thank you!

Thanks to all co-authors, within the @dulaclab.bsky.social - @blogeman.bsky.social, Tate Yawitz, Mustafa Talay, and Changwoo Seo, and collaborators: Kai Zhang & Bing Ren, Celine Santiago & David Ginty, and Noor Sohail, Serhiy Naumenko, & Shannan Ho Sui.

In summary, we described the molecular programs that make up preoptic area cell type development, and showed how the maturation of these cell types depends in part on external inputs.

We also did a deep dive into (1) the development of signaling pathways important for various hypothalamic functions, such as sleep and social behavior, and (2) the emergence of sex differences in gene expression.

Adults showed only subtle differences in gene expression, indicating that cell types eventually “catch up” in their maturation. Future work will address whether these gene expression differences cause any of the dramatic effects on social behavior previously reported in adult Trpc2 mutants.

We found that this difference amounts to a transient developmental delay in the maturation of preoptic area cell types.

To address this, we sequenced the POA in mutant mice impaired in various sensory modalities. This revealed little to no effect of bodily touch, olfaction, cold sensation or vision. However, in Trpc2 mutants, which lack pheromone sensation through the vomeronasal organ, many cell types were affected.

However, it’s possible that the causality is the other way around: cell types may mature in response to other changes in the animal. For example, early life social experience can have long-lasting impacts on sociality into adulthood, suggesting the existence of critical periods in early life.

This suggests that the timing of gene expression changes correlates with the timing of changes in the behavior that the cell type is involved in. While these data are intriguing, future work must be done to show how these gene expression changes relate to changes in cell type function.

Cell types involved in social behavior matured especially late, consistent with social behavior changing dramatically with puberty. Cell types involved in sleep showed major changes from P10 to P18, which is the same time as dramatic changes in sleep behavior in mice.

This revealed diverse maturation trajectories. Some cell types matured gradually, others more non-linearly. Some matured early, others late. We found that these differences depend in part on the cell type’s sub-regional location within the preoptic area, its function, and the sex of the animal.

While cell type identity is diversified very early on, cell types are not yet mature – their gene expression differs from their adult states. We asked whether different cell types mature along distinct trajectories, by measuring similarity to the adult state at each younger age.

When does this diversity first emerge? We sequenced at E14, an age where ~half of the POA cells are dividing progenitors, and the other half are newborn neurons. These data revealed that diversification occurs rapidly upon neurogenesis.

To quantify this, we used CCA-based label transfer, and found that indeed each E16 cell type maps onto just a single adult cell type. This indicates that the full complement of ~150 cell types is already diversified well before birth.

Each cell type's developmental trajectory appeared as a gradient in UMAP space. This intriguingly suggested that cell types are diversified very early in life – as early as embryonic day 16 (E16), based on the grouping of those cells with adult cell types.

The dataset is massive: 200,000 cells and ~150 cell types, ~25% of which have known behavioral annotations thanks to previous work by many labs, such as @dulaclab.bsky.social work on parenting or social drive (recently published by @dingliu.bsky.social). Maybe you can spot your favorite cell type!

Preoptic cell types have been defined using single-cell RNA-seq in adults, so we used snRNA-seq to ask whether we can identify these cell types early in life, and how they might differ molecularly from adult cell types.

These cell types have been studied extensively in adults, but not earlier. Social behavior and homeostasis change dramatically with age. For example, infants meet homeostatic needs like thirst or warmth through social interactions, so these cell types may function differently early in life.

We focused on the mouse hypothalamic preoptic area (POA), a brain region containing genetically defined cell types that have been linked to specific social behaviors, such as parenting, and homeostatic functions, such as sleep.