Comprehensive circRNA Profiling Reveals a Testis-Specific circRNA circdmrt1 as a Novel Regulator of Gonadal Development in Crucian Carp

Fish gonad development is a central process in reproductive regulation, and elucidating its molecular mechanisms is highly important for developing aquatic genetic resources. However, the involvement of circular RNAs (circRNAs) in the gonad development of freshwater fish is unknown. In this study, a dynamic expression profile of circRNA during the development of red crucian carp testes was systematically constructed via whole-transcriptome sequencing. Notably, the circular characteristics and high testis-specific expression of the key circRNA circdmrt1, formed through the reverse splicing of the fourth exon of the dmrt1 gene, have been experimentally validated. The overexpression of circdmrt1 promoted cell proliferation and inhibited the expression of apoptosis-related genes. Furthermore, in the hybrid offspring of red crucian carp and white crucian carp, circdmrt1 expression exhibited a pronounced paternal-line-biased pattern. Our data reveal that circdmrt1 may act as a ceRNA by sequestering miR-122-5p and thereby modulating DHRSX expression, leading to the activation of HEK-293T cell proliferation. This study reveals for the first time the regulatory features of testicular circRNAs in crucian carp, providing support evidence into the mechanisms of gonadal development in teleosts.