Sex-specific splicing occurs genome-wide during early Drosophila embryogenesis.

Sex-specific splicing is an essential process that regulates sex determination and drives sexual dimorphism. Yet, how early in development widespread sex-specific transcript diversity occurs was unknown because it had yet to be studied at the genome-wide level. We use the powerful Drosophila model to show that widespread sex-specific transcript diversity occurs early in development, concurrent with zygotic genome activation. We also present a new pipeline called time2splice to quantify changes in alternative splicing over time. Furthermore, we determine that one of the consequences of losing an essential maternally-deposited pioneer factor called CLAMP (Chromatin linked adapter for MSL proteins) is altered sex-specific splicing of genes involved in diverse biological processes that drive development. Overall, we show that sex-specific differences in transcript diversity exist even at the earliest stages of development.