In the secretory signaling pathways, SPP1 (osteopontin) is upregulated in uM1 and uM2 in the PCOS-endometrium, forming ligand–receptor pairs with ITGA9 (upregulated in uM2), ITGAV (in SOX9+LGR5+, AR+ and uM1) and ITGB1 (in AR+ and uM1) (Fig. 5b and Supplementary Table 4a–e). Here, SPP1 is linked to polycystic ovary syndrome.