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In the early stages of meiosis, maternal and paternal chromosomes pair with their homologous partner and recombine to ensure exchange of genetic information and proper segregation. These events can vary drastically between species and between males and females of the same species. In Drosophila, in contrast to females, males do not form synaptonemal complexes (SCs), do not recombine, and have no crossing over; yet, males are able to segregate their chromosomes properly. Here, we investigated the early steps of homolog pairing in Drosophila males. We found that homolog centromeres are not paired in germline stem cells (GSCs) and become paired in the mitotic region before meiotic entry, similarly to females. Surprisingly, male germline cells express SC proteins, which localize to centromeres and promote pairing. We further found that the SUN/KASH (LINC) complex and microtubules are required for homolog pairing as in females. Chromosome movements in males, however, are much slower than in females and we demonstrate that this slow dynamic is compensated in males by having longer cell cycles. In agreement, slowing down cell cycles was sufficient to rescue pairing-defective mutants in female meiosis. Our results demonstrate that although meiosis differs significantly between males and females, sex-specific cell cycle kinetics integrate similar molecular mechanisms to achieve proper centromere pairing. [ABSTRACT FROM AUTHOR]

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 homolog of Spo11 , to assess its expression at both the mRNA and protein levels and used different mutant alleles to assay for a premeiotic 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. [ABSTRACT FROM AUTHOR]

Immunocytochemical analysis of meiotic proteins on mouse chromosome spreads is one method of choice to study prophase I chromosome organization and homologous recombination. In recent decades, the development of microscopic approaches led to the production of a large number of images that monitor fluorescent proteins, defined as fluorescent objects, and a major challenge facing the community is the deep analysis of these fluorescent objects (measurement of object length, intensity, distance between objects, as well as foci identification, counting, and colocalization). We propose a set of tools designed from the macro language of the widely used image analysis software ImageJ (Schindelin et al., Nat Methods 9: 676-682, 2012), embedded in the "MeiQuant" macro, which are specifically designed for analyzing objects in the field of meiosis. Our aim is to propose a unified evolutive common tool for image analysis, with a specific focus on mouse prophase I meiotic events., (© 2024. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)