Evolutionary dynamics of sex determination in Branchiostoma belcheri driven by repeated transposition of a single novel gene.

ABSTRACT: Sex determination systems display striking evolutionary flexibility, yet the mechanisms underlying their transitions remain poorly understood. Using newly generated genome assemblies, we investigated the evolving sex-determining system in the amphioxus Branchiostoma belcheri. We identified two female-specific sex-determining regions (SDRs) on chromosome 13, both derived from independent transpositions of the autosomal gene tesD, which shows testis-specific expression in amphioxus species. CRISPR/Cas9 knockout experiments in Branchiostoma floridae confirmed that tesD functions as a male-determination gene, with loss of function producing an all-female phenotype. In B. belcheri, the older SDR (tesDwa) inserted into the coding region of twai, while the younger SDR (tesDwb), flanked by active

SUBMITTER: Li H 

PROVIDER: S-EPMC12905397 | biostudies-literature | 2026 Jan

REPOSITORIES: biostudies-literature