PLK1 depletion alters homologous recombination and synaptonemal complex disassembly events during mammalian spermatogenesis

Abstract

Homologous recombination (HR) is an essential meiotic process that contributes to the genetic variation of offspring and ensures accurate chromosome segregation. Recombination is facilitated by the formation and repair of programmed DNA double-strand breaks. These DNA breaks are repaired via recombination between maternal and paternal homologous chromosomes and a subset result in the formation of crossovers. HR and crossover formation is facilitated by synapsis of homologous chromosomes by a proteinaceous scaffold structure known as the synaptonemal complex (SC). Recent studies in yeast and worms have indicated that polo-like kinases (PLKs) regulate several events during meiosis, including DNA recombination and SC dynamics. Mammals express four active PLKs (PLK1-4), and our previous work assessing localization and kinase function in mouse spermatocytes suggested that PLK1 coordinates nuclear events during meiotic prophase. Therefore, we conditionally mutated Plk1 in early prophase spermatocytes and assessed stages of HR, crossover formation, and SC processes. Plk1 mutation resulted in increased RPA foci and reduced RAD51/DMC1 foci during zygonema, and an increase of both class I and class II crossover events. Furthermore, disassembly of SC lateral elements was aberrant. Our results highlight the importance of PLK1 in regulating HR and SC disassembly during spermatogenesis.

Kinase PLK1 regulates the disassembly of the lateral elements and the assembly of the inner centromere during the diakinesis/metaphase I transition in male mouse meiosis

“…These data suggest that the SYCP3 and HORMAD1 proteins that normally accumulate at the inner centromeres in prometaphase I bivalents derive from the population of proteins that are previously released from the LEs throughout the diakinesis stage. Altogether, our results strongly support previous results ( Ishiguro et al, 2011 ; Wellard et al, 2022 ) indicating that PLK1 regulates the disassembly of the LEs during the diakinesis/metaphase I transition by enabling the release not only of SYCP3, but also of HORMAD1. Since during budding yeast meiosis Cdc5/PLK1 also controls this disassembly ( Sourirajan and Lichten, 2008 ; Argunhan et al, 2017 ), we suggest that PLK1 could be considered as a master kinase that controls this meiotic process.…”

“…Accordingly, these authors proposed that PLK1 might promote the release of SYCP3 during late prophase I stages. In addition, it has been recently observed that in Plk1 cKO male mice the disassembly of the LEs is aberrant ( Wellard et al, 2022 ). In this sense, the LE proteins SYCP3 and SYCP2 were retained at the interchromatid domain of metaphase I bivalents, and these proteins were absent at the centromeres.…”

“…In this sense, the LE proteins SYCP3 and SYCP2 were retained at the interchromatid domain of metaphase I bivalents, and these proteins were absent at the centromeres. These results led the authors to propose that PLK1 is required for LEs disassembly ( Wellard et al, 2022 ). We have found that after the in vitro inhibition of the kinase activity of PLK1 with BI 2536 altered diakinesis spermatocytes show a continuous labeling of SYCP3 and HORMAD1 along the desynapsed LEs.…”

“…It is worth noting that we have found that PLK1 phosphorylated at serine S137 (PLK1S137ph) is present along the AEs/LEs during all prophase I stages, and at bulges and thickenings along desynapsed LEs in late diplotene and diakinesis spermatocytes. The phosphorylation of PLK1S137ph is necessary to activate PLK1 to phosphorylate some targets in the S interphase stage ( Jang et al, 2002 ), and has been detected in mouse oocytes ( Du et al, 2015 ; Feitosa et al, 2018 ) and spermatocytes ( Wellard et al, 2022 ). Our results suggest that this active phosphorylated form of PLK1 is at the right place to mediate the phosphorylation of the LE proteins leading to their release.…”

“…PLK1 phosphorylates the CE proteins SYCP1 and TEX12 to allow desynapsis of homolog LEs ( Jordan et al, 2012 ). Interestingly, it has been recently reported that the kinases Aurora B and C, as well as PLK1, regulate the disassembly of LEs during the late prophase I/metaphase I transition ( Wellard et al, 2020 ; Wellard et al, 2022 ).…”