Genetic Interactions Between the Meiosis-Specific Cohesin Components, STAG3, REC8, and RAD21L

Abstract

Cohesin is an essential structural component of chromosomes that ensures accurate chromosome segregation during mitosis and meiosis. Previous studies have shown that there are cohesin complexes specific to meiosis, required to mediate homologous chromosome pairing, synapsis, recombination, and segregation. Meiosis-specific cohesin complexes consist of two structural maintenance of chromosomes proteins (SMC1α/SMC1β and SMC3), an α-kleisin protein (RAD21, RAD21L, or REC8), and a stromal antigen protein (STAG1, 2, or 3). STAG3 is exclusively expressed during meiosis, and is the predominant STAG protein component of cohesin complexes in primary spermatocytes from mouse, interacting directly with each α-kleisin subunit. REC8 and RAD21L are also meiosis-specific cohesin components. Stag3 mutant spermatocytes arrest in early prophase (“zygotene-like” stage), displaying failed homolog synapsis and persistent DNA damage, as a result of unstable loading of cohesin onto the chromosome axes. Interestingly, Rec8, Rad21L double mutants resulted in an earlier “leptotene-like” arrest, accompanied by complete absence of STAG3 loading. To assess genetic interactions between STAG3 and α-kleisin subunits RAD21L and REC8, our lab generated Stag3, Rad21L, and Stag3, Rec8 double knockout mice, and compared them to the Rec8, Rad21L double mutant. These double mutants are phenotypically distinct from one another, and more severe than each single knockout mutant with regards to chromosome axis formation, cohesin loading, and sister chromatid cohesion. The Stag3, Rad21L, and Stag3, Rec8 double mutants both progress further into prophase I than the Rec8, Rad21L double mutant. Our genetic analysis demonstrates that cohesins containing STAG3 and REC8 are the main complex required for centromeric cohesion, and RAD21L cohesins are required for normal clustering of pericentromeric heterochromatin. Furthermore, the STAG3/REC8 and STAG3/RAD21L cohesins are the primary cohesins required for axis formation.

Sororin is enriched at the central region of synapsed meiotic chromosomes

“…The meiosis-specific SMC1β subunit is required for normal axis formation, chromosome loop size, and recombination in meiotic prophase I (Revenkova et al 2004; Novak et al 2008; Biswas et al 2013). The analysis of compound meiotic cohesin mutants confirms both that STAG3-containing cohesins are essential for normal axis formation, and that STAG3 has functional interactions with both the REC8 and RAD21L kleisins (Ward et al 2016). …”

“…The Stag3 mouse mutant strain used in this study has previously been described (Hopkins et al 2014; Ward et al 2016). Briefly, the Stag3 allele was created by integration of the SB-cHS4core-SB-Tyro-WPRE-FUGW lentiposon transgene (LV2229) in intron 8 of Stag3 (http://www.mmrrc.org/catalog/sds.php?mmrrc_id=36275) in an FVB background.…”

“…Mutations in genes encoding meiosis-specific cohesin subunits confirm that these isoforms are essential for normal chromosome axis formation, synapsis, and double-strand break formation and repair (Xu et al 2004; Bannister et al 2004; Xu et al 2005; Fukuda et al 2010; Winters et al 2014; Ward et al 2016). The unique phenotypes and patterns of association of the different meiotic cohesin complexes with chromosome axes during pairing and synapsis in meiotic prophase also suggest non-overlapping roles in meiotic chromosome dynamics (reviewed in (Rankin 2015)).…”

STAG1mutations cause a novel cohesinopathy characterised by unspecific syndromic intellectual disability

“…It was demonstrated that STAG2 was required for centromeric cohesion, whereas STAG3 was required to stabilise cohesin on chromosome axes and STAG1 had a specific role in telomere cohesion 9 28. Besides its canonical role in chromosome segregation, the cohesin complex indeed directly influences transcription via an essential role in transcriptional enhancer function 2.…”

Distinct Roles of Meiosis-Specific Cohesin Complexes in Mammalian Spermatogenesis

“…In the complete STAG3 deficiency, the cells develop maximally to a testis tubular stage IV, but chromosomally they reflect leptotene cells as there are no axes (Winters et al, 2014). Very recently, double mutants of Stag3 with either Rec8 or Rad21L were described and show increased centromeric cohesion defects, very short AEs and, in case of the Stag3 -/- Rec8 -/- strain, are similar in phenotype to the Rec8 -/- Rad21L -/- spermatocytes [23]. …”