overview of gene expression dynamics during sheep early ovarian folliculogenesis. Ovis aries

Background Successful achievement of early folliculogenesis is crucial for female reproductive function. It requires the appropriate expression of many genes at different developmental stages, in the different cell types and implies cell-cell interactions. To date most of the gene expression studies were conducted on rodent oocytes and granulosa cells (GC) transcriptome is lacking yet, due to their limited availability. We used a Laser Microdissection Capture method combined with RNA-seq technology to explore overall transcriptome either in oocytes and GC during sheep early folliculogenesis and provide an overview of specific mechanisms and functions implemented in these two cell-types. Results We documented the expression profile of 15,349 genes, and then focused on the 5,129 genes that showed a differential expression between oocytes and GC. Enriched functional categories such as oocyte meiotic arrest and GC steroid synthesis reflect the two distinct cell fates. We observed a fine regulation of follicular atresia and the involvement of angiogenesis genes. We reinforced the role of GH factors as PDGF, ARH, HGF and reported the implication of GC signal transduction pathways as SSH, WINT and RHO GTPase. In addition, signaling pathways (VEGF, NOTCH, IGF1…) and GC transzonal projections pointed out the existence of complex cell-cell interactions. Finally, we highlighted several transcription regulators and specifically expressed genes that are likely to assume an important role in preantral stages. Conclusions We present, to our knowledge, the first comprehensive exploration of transcriptomes derived from “in vivo” oocytes and GC at key stages of sheep early follicular development. Collectively, our data contribute to a better understanding of the early folliculogenesis in nono-ovulating species and will serve as a valuable resource for unraveling human ovarian dysfunction as premature ovarian failure (POF)