Key up- and downregulated DEGs in PCOS in stroma 1 and stroma 2, which were not differentially expressed in any other subpopulation, included PIK3C2G (downregulated), a gene associated with granulosa cell tumor29, MAP3K5 (upregulated), a marker of human endometrial receptivity30, and the collagen gene COL7A1 (upregulated), a component of the basement membrane and surrounding vasculature that plays an important role in regulating tissue remodeling and homeostasis31 (Fig. 3e and Supplementary Table 2a–c). Here, COL7A1 is linked to polycystic ovary syndrome.