Spatiotemporal single-cell RNA sequencing of chick ovary identifies ovarian niche during primordial follicle formation and activation

The reproductive lifespan of female animals depends on the size and maintenance of their primordial follicle pool, which is determined by the processes of the primordial follicle formation and activation. However, the avian primordial follicle formation and activation process has not yet been revealed. Here, single-cell RNA sequencing and spatial transcriptome were combined to explored the chicken primordial follicle formation and activation. The morphological analysis of chicken ovaries indicated that primordial follicles are initially formed around the 5th day post-hatch, while their activation takes place around the 10th day post-hatch. In this work, a high-resolution single-cell spatial transcriptional atlas of the chicken ovary was revealed for the first time. The heterogeneity, microenvironment and intercellular communication of the chicken ovary were elucidated during the primordial follicle formation and activation. Interestingly, we discovered that the signaling pathway of the cholesterol-steroid hormone biosynthesis is crucial for the chicken primordial follicle formation, but not mice. GREB1 (Growth Regulating Estrogen Receptor Binding 1) was identified as one of the downstream effectors in the cholesterol-steroid hormone biosynthesis signaling pathway during the chicken primordial follicle formation. These results provide a comprehensive understanding of chicken primordial follicle formation and activation and offer a new perspective for exploring the avian primordial follicle formation.