Single-cell lineage tracing uncovers unique skin adipose hierarchy and Sox9-mediated differentiation of adipocyte precursors
White adipose tissue is essential to various physiological functions, with adipocyte precursor cells (APCs)—comprised of progenitors and preadipocytes—playing a pivotal role in generating mature adipocytes during the expansion of adipose depots. Here, using single-cell RNA sequencing-based lineage tracing, we characterize APC populations in the skin, a depot distinguished by its uniquely rapid and efficient adipogenesis relative to other sites, such as inguinal adipose. We identify a previously uncharacterized population of immature preadipocytes and reveal a biased differentiation potential among APCs. Contrary to the step-wise differentiation paradigm proposed to yield mature adipocytes, progenitor cells represent the primary source of committed preadipocytes, while preexisting preadipocytes accumulate in immature states with distinct potential. We use this framework of cell heterogeneity and lineage in skin adipose to investigate the mechanisms of APC differentiation, identifying Sox9 as a crucial regulator of precursor proliferation and differentiation. Finally, via cross-depot transplantation, we define intrinsic and extrinsic factors that influence the behavior of skin progenitors, highlighting the contrasting dynamics between skin and inguinal depots. These findings provide a deeper understanding of the specific dynamics and molecular mechanisms underlying rapid adipogenesis in skin adipose tissue. Overall design: Skin adipocyte precursors were isolated by Fluorescence-activated cell sorting (FACS) according to markers of subpopulations, CellTagged, transplanted into P21 mice, and analyzed by scRNA-seq.