Decoding genome recombination and sex reversal

The swamp eel is an increasingly recognized model organism for reproductive, developmental, and genetic studies. Whole genome-wide chromosome fission/fusion events occurred during speciation of the swamp eel, and probably contributed to species survival. Female transforms its sex naturally to male through an intersexual phase. Histologically, the ovary becomes a testis via a transition of ovotestis. Progenitors of germline stem cells can be identified in ovotestis, which have bipotential to differentiate into either male or female germline stem cells. The sex reversal process is involved in two molecular mechanisms, degradation of female germline cells by ubiquitination-dependent proteasome/phase separation, autophagy, and apoptosis, and spermatogenesis arrest due to dysregulation of histone-to-protamine replacement in ovotestis. Over the past 440 years since the discovery of the medicinal value of swamp eels, much progress has been made in the study of their biology. The fish is emerging as an important model animal in sexual development, in addition to economic and pharmaceutical implications. Tracing genomic history that shapes speciation of the fish has led to discovery of the whole genome-wide chromosome fission/fusion events. Natural intersex differentiation is a compelling feature for sexual development research. Notably, identification of progenitors of germline stem cells that have bipotential to differentiate into either male or female germline stem cells provides new insight into sex reversal. Here, we review these advances that have propelled the field forwards and present unsolved issues that will guide future investigations to finally elucidate vertebrate sexual development using the new model. Over the past 440 years since the discovery of the medicinal value of swamp eels, much progress has been made in the study of their biology. The fish is emerging as an important model animal in sexual development, in addition to economic and pharmaceutical implications. Tracing genomic history that shapes speciation of the fish has led to discovery of the whole genome-wide chromosome fission/fusion events. Natural intersex differentiation is a compelling feature for sexual development research. Notably, identification of progenitors of germline stem cells that have bipotential to differentiate into either male or female germline stem cells provides new insight into sex reversal. Here, we review these advances that have propelled the field forwards and present unsolved issues that will guide future investigations to finally elucidate vertebrate sexual development using the new model.