Dissecting the transcriptomic signature of porcine oocyte during primordial follicle formation from single cell resolution

BACKGROUND: Ovarian reserve, refers to the number of primordial follicle (PF) in mammals, is a decisive factor affecting the reproductive lifespan of females. However, the molecular mechanism of PF formation has not been fully elucidated, especially in large mammals. In the study, the ovarian tissues at embryonic day 95 (E95) and postnatal day 0 (PD0) were collected for single-nucleus transcriptome sequencing, attempting to investigate the transcriptome dynamic of porcine oocyte during PF formation at a single-cell level. RESULTS: In the results, we identified in detail three germ cell clusters with different transcriptional modes. Moreover, through a comparative analysis of developmental trajectory in pig, mouse and monkey, several conserved regulatory genes that associated with the developmental fate of germ cells were identified. By employing SCENIC software, we identified 27 transcription factors specific to developmental stages of germ cells. In addition, a protein interaction network between transcription factors and conserved genes was constructed and it discovered a key transcription factor, enhancer of zeste homolog 2 (EZH2), which is expressed exclusively in oocytes during PF formation, and there is the asynchrony of its expression in germ cells between the medulla and cortex regions. Further, during the in vitro culture of mouse ovaries, the inhibition of EZH2 expression significantly decreased the number of oocytes and leading to the decline of protein expressions that essential for PF formation. CONCLUSIONS: This study provides a single-cell map of pig ovary in the late embryonic development and newly born periods, and enriches the public understanding of primordial follicle formation in mammals.