Transcriptomic analysis of meiotic genes during the mitosis-to-meiosis transition in Drosophila females

Germline cells produce gametes, which are specialized cells essential for sexual reproduction. Germline cells first amplify through several rounds of mitosis before switching to the meiotic program, which requires specific sets of proteins for DNA recombination, chromosome pairing and segregation. Surprisingly, we previously found that some proteins of the synaptonemal complex, a prophase I meiotic structure, are already expressed and required in the mitotic region of Drosophila females. Here, to assess if additional meiotic genes were expressed earlier than expected, we isolated mitotic and meiotic cell populations to compare their RNA content. Our transcriptomic analysis reveals that all known meiosis I genes are already expressed in the mitotic region, however, only some of them are translated. As a case study, we focused on mei-W68, the Drosophila homologue of Spo11, to assess its expression at both the mRNA and protein levels, and used different mutant alleles to assay for a pre-meiotic function. We could not detect any functional role for Mei-W68 during homologous chromosome pairing in dividing germ cells. Our study paves the way for further functional analysis of meiotic genes expressed in the mitotic region. Article SummaryGermline cells, crucial for sexual reproduction, were thought to switch to meiosis only after several rounds of mitosis. Surprisingly, a few meiotic proteins were found active in the mitotic phase of female flies. Here, we discovered that all known meiosis genes were expressed during mitosis, but only some produced proteins. This study suggests that genes related to reproduction are active earlier than expected, prompting further exploration into their functions during early cell division.