Rad21l1 cohesin subunit is dispensable for spermatogenesis but not oogenesis in zebrafish

Abstract

Meiosis produces haploid gametes that will give rise to the next diploid generation. Chromosome segregation errors occurring at one or both meiotic divisions result in aneuploidy, which can lead to miscarriages or birth defects in humans. During meiosis I, ring-shaped cohesin complexes play important roles to aid in the proper segregation of homologous chromosomes. While REC8 is a specialized meiosis-specific cohesin that functions to hold sister chromatids together, the role of its vertebrate-specific paralog, RAD21L, is poorly understood. Here we tested if Rad21l1, the zebrafish homolog of human and mouse RAD21L, is required for meiotic chromosome dynamics during oogenesis and spermatogenesis. We found that Rad21l1 is an abundant component of meiotic chromosomes where it localizes to both the chromosome axes and the transverse filament of the synaptonemal complex (SC). Knocking out rad21l1 causes nearly the entire mutant population to develop as fertile males, suggesting the mutation triggers a sex reversal from female to male due to a failure in oocyte production. The rad21l1−/− mutant males display normal fertility at sexual maturity. Sex reversal was partially suppressed in the absence of tp53, suggesting that the rad21l1−/− mutation causes defects leading to a Tp53 dependent response, specifically in females. The rad21l1−/−;tp53−/− double mutant females produced elevated rates of decomposing eggs and deformed offspring compared to tp53−/− controls. This response, however, is not linked to a defect in repairing Spo11-induced double-strand breaks since deletion of Spo11 does not suppress the sex reversal phenotype. Overall, our data highlight an exceptional sexually dimorphic phenotype caused by knocking out a meiotic-specific cohesin subunit. We propose that Rad21l1 is required for maintaining the integrity of meiotic chromatin architecture during oogenesis.Author SummaryA prominent symptom of age-linked reproductive decline in women is the increased rate of miscarriage and birth defects due to aneuploidy. Aneuploidy can arise when chromosomes fail to segregate properly during meiosis, the process of creating haploid gametes from a diploid germ cell. Oocyte progression normally arrests prior to anaphase I, after homologous chromosomes have formed crossovers, but before ovulation, which triggers the first round of segregation. This prolonged arrest makes oocytes especially vulnerable to degradation of meiotic chromosome structure and homolog connections over time. Cohesin complexes play a major role in maintaining the meiotic chromosome architecture. Here we assess the role of the vertebrate-specific Rad21l1 cohesin subunit in zebrafish. We find that while males appear mostly unaffected by loss of Rad21l1, oocyte production is massively compromised, leading to sex reversion to males. Sex reversion can be partially prevented in the absence of Tp53, demonstrating that loss or Rad21l1 leads to a Tp53-dependent response in oocytes. Strikingly, double mutant rad21l1 tp53 females produce large numbers of poor quality eggs and malformed offspring. This demonstrates a cohesin-linked vulnerability in female meiosis not present in males and sheds light on a potential mechanism associated with the decline in female reproductive health.

The RNA-binding protein Adad1 is necessary for germ cell maintenance and meiosis in zebrafish

“…Zebrafish mutants disrupting genes encoding synaptonemal complex proteins sycp1 , sycp2 , and sycp3 as well as the meiotic cohesion component smc1b , developed as 100% sterile males due to failures in meiotic prophase I (73–75,78). Mutations that specifically effect female meiosis, such as mutations in zar1 and rad21l1 , failed to develop as female or were male biased, respectively (54,76). In these mutants, males were normal indicating a requirement in female meiosis but not spermatogenesis (54,76).…”

“…Mutations that specifically effect female meiosis, such as mutations in zar1 and rad21l1 , failed to develop as female or were male biased, respectively (54,76). In these mutants, males were normal indicating a requirement in female meiosis but not spermatogenesis (54,76). We demonstrated that adad1 mutant spermatocytes failed to progress beyond the zygotene stage and that ovarian follicles were never formed in the bipotential gonad stage.…”

Rad21l1 cohesin subunit is dispensable for spermatogenesis but not oogenesis in zebrafish

“…Images of eggs and embryos were acquired using a dissecting microscope. All data and related metadata underlying the findings have been deposited and are available at DRYAD (doi: 10.25338/B8V91Q) [81].…”

A Hypothesis: Linking Phase Separation to Meiotic Sex Chromosome Inactivation and Sex-Body Formation

“…Testis-specific H1 histone (H1t) 0.714 Associated with repressed chromatin domains in pachytene spermatocytes (Mahadevan et al, 2020) Mediator of DNA damage checkpoint protein 1 (MDC1) 0.697 Functions in chromosome-wide silencing of the sex body (Ichijima et al, 2011) TP53-binding protein 1 (53BP1) 0.624 DDR protein and localizes to the sex body (Lu et al, 2013) Histone-lysine N-methyltransferase SETDB1 0.338 Links meiotic DDR to sex chromosome silencing (Hirota et al, 2018) Pachytene checkpoint protein 2 homolog (Trip13) 0.338 Required for recombination and meiotic chromosome structure (Roig et al, 2010) Synaptonemal complex protein 3 (SYCP3) 0.256 Component of synaptonemal complex (Syrjänen et al, 2014) Cohesin subunit SA-3 (STAG3) 0.173 Maintaining centromere chromatid cohesion; required for DSB repair and synapsis (Hopkins et al, 2014) DNA mismatch repair protein Mlh1 0.146 Homologous recombination and DSB repair (Cannavo et al, 2020) Synaptonemal complex protein 2 (SYCP2) 0.144 Component of synaptonemal complex (Feng et al, 2017) Serine/threonine-protein kinase Chk1 0.137 DNA damage response (Nie et al, 2017) Meiotic recombination protein REC8 0.124 Sister-chromatid cohesion and crossover recombination (Yoon et al, 2016) HORMA domain-containing protein 1 (HORMAD1) 0.094 Synaptonemal complex formation, recombination and chromosome segregation (Shin et al, 2010) Double-strand-break repair protein rad21-like protein 1 (Rad21L1) 0.038 Maintaining the integrity of meiotic chromatin architecture (Blokhina et al, 2020) Synaptonemal complex protein 1 (SYCP1) 0.036 Component of synaptonemal complex (de Vries et al, 2005) Serine-protein kinase ATM 0.026 Controlling DSB formation and recombination (Lange et al, 2011;Kurzbauer et al, 2021) and exert specific biological functions (Mackenzie et al, 2017).…”