Deciphering Gamete Differentiation in Ostrea edulis using Laser Capture Microdissection and RNA-seq.

Molluscs exhibit high sexual plasticity, with sequential hermaphroditism being particularly widespread among oysters. Although some key gene pathways are conserved, the transcriptional regulatory networks controlling the gamete development in oysters remain limited. The European flat oyster, Ostrea edulis, serves as an ideal model for deciphering this alternating protandrous hermaphroditism. This study used a laser capture microdissection (LCM) coupled with bulk RNA sequencing approach to investigate the transcriptomic dynamics during gamete development. This study showed that gonia cells represent an immature, proliferative, and highly plastic germ-cell population, with a transcriptomic program largely shared between the male and female developmental pathways. We evidence the importance of transcriptional reprogramming during the transition from gonia cells to primary spermatocytes, the extensive remodeling of the gonadal microenvironment at the secondary spermatocyte stage and the role of lipid metabolism and membrane remodeling in the spermatid maturation. We also characterized that early oocyte development is associated with activation of meiotic, cell-cycle, proteostasis, and metabolic pathways and that oocyte maturation involves coordinated genome maintenance, ovarian differentiation, nutrient accumulation, and epigenetic regulation. This study is the first conducted in O edulis describing in details both spermatogenesis and oogenesis, evidencing new molecular pathways that are still poorly studied in oysters.