Single-cell transcriptomics reveals the differential landscape of gonadal cells during MT-induced sex reversal in hermaphroditic protogynous orange-spotted grouper (Epinephelus coioides)

Background Sex reversal is an intricate and fascinating process orchestrated by a finely organized network. The orange-spotted grouper ( Epinephelus coioides ) is a protogynous hermaphroditic fish, but the regulatory mechanism of its sex reversal is not yet well understood. Results Here, single-cell transcriptome sequencing (scRNA-seq) of the gonads was performed during sex reversal induced by 17α-methyltestosterone (MT). Based on the scRNA-seq data, various gonadal cell types and subtypes, including eight types of germ cells and nine types of somatic cells, were characterized and identified. Moreover, a single-cell atlas of dynamic changes in gene expression during sex reversal in orange-spotted grouper was constructed. We outlined the precise trajectories of germ stem cells (GSCs) and male somatic cells, which revealed that new male germ cells were originated from a subcluster of GSCs with increased levels of spermatogenesis genes. Moreover, we revealed that piwil1 and dmrt1 were important for the male-oriented differentiation of GSCs. Additionally, oocytes exhibited abnormal and significant apoptosis and active proliferation during the early stage of sex reversal. Conclusions Overall, these results address the questions of how male germ cells are generated and how female germ cells disappear during sex reversal in orange-spotted grouper. These findings profile a comprehensive dynamic map of gonadal cells during sex reversal, which can provide new insights into sex change in lower vertebrates.