BMP2 is required for granulosa cell proliferation and primordial follicle activation in chicken

During ovary development, the dormant primordial follicles (PF) are stimulated and begin to develop into primary follicles (PrF), a process called follicle activation. Only activated follicles can continue to grow and release the eggs in the future, making the female animal fertile. The molecular events during PF activation are not fully understood. In this study, we analyzed the transcriptome of ovarian granulosa cells (GCs) before and after PF activation from 4- and 7-day-old chicks and identified that BMP signaling was induced during this process. Further, exogenous addition of Bone Morphogenetic Protein-2 (BMP2) protein significantly promotes the proliferation of GCs, thereby increasing the number of PrF in the in vitro ovary culture system. Conversely, when the BMP2 was blocked, the proliferation of GCs is inhibited, leading to a decrease in the number of PrF generated. These findings reveal the critical role of BMP2 in regulating the activation of chicken PF and provide new strategies for improving egg production performance.