Single-cell-scale spatial transcriptome reveals early regional priming of the developing mouse ovary

Mammalian ovary development is essential for female fertility, involving the complex spatial patterning of diverse cell types to establish the finite reserve of ovarian follicles. To uncover molecular mechanisms driving regionalization of the ovary while maintaining its native cellular architecture, we used Visium HD spatial transcriptomics. Our study captures all ovarian cell types at eight timepoints, generating a near single cell resolution library of spatial gene expression across development. Our analysis identified a previously uncharacterized "medullary core" domain that emerges by E16.5. Pre-granulosa cells (PGs) within this core express genes typically restricted to growing follicles in the postnatal ovary (Nr5a2, Slc18a2, Ephx2) suggesting core PGs are poised for activation while still in the fetal environment. This study provides a comprehensive architectural and molecular blueprint of the ovary, representing a fundamental resource for the investigation of regulatory mechanisms driving spatial patterning of the ovary and opens new avenues to explore the spatial determinants of female fertility and reproductive longevity.