Meiosis-specific cohesin complexes display essential and distinct roles in mitotic embryonic stem cell chromosomes

Abstract

Background Cohesin is a chromosome-associated SMC–kleisin complex that mediates sister chromatid cohesion, recombination, and most chromosomal processes during mitosis and meiosis. However, it remains unclear whether meiosis-specific cohesin complexes are functionally active in mitotic chromosomes. Results Through high-resolution 3D-structured illumination microscopy (3D-SIM) and functional analyses, we report multiple biological processes associated with the meiosis-specific cohesin components, α-kleisin REC8 and STAG3, and the distinct loss of function of meiotic cohesin during the cell cycle of embryonic stem cells (ESCs). First, we show that STAG3 is required for the efficient localization of REC8 to the nucleus by interacting with REC8. REC8-STAG3-containing cohesin regulates topological properties of chromosomes and maintains sister chromatid cohesion. Second, REC8-cohesin has additional sister chromatid cohesion roles in concert with mitotic RAD21-cohesin on ESC chromosomes. SIM imaging of REC8 and RAD21 co-staining revealed that the two types of α-kleisin subunits exhibited distinct loading patterns along ESC chromosomes. Third, knockdown of REC8 or RAD21-cohesin not only leads to higher rates of premature sister chromatid separation and delayed replication fork progression, which can cause proliferation and developmental defects, but also enhances chromosome compaction by hyperloading of retinoblastoma protein–condensin complexes from the prophase onward. Conclusions Our findings indicate that the delicate balance between mitotic and meiotic cohesins may regulate ESC-specific chromosomal organization and the mitotic program.

The Kleisin Subunits of Cohesin Are Involved in the Fate Determination of Embryonic Stem Cells

“…Interestingly, relative expression levels of OCT3/4 to GAPDH were drastically decreased in cohesin-knockdown conditions compared with the levels in the control group, meaning that each cohesin subunit, especially RAD21 and SMC3, somehow decreases the level of OCT3/4, raising the possibility that it stimulates the differentiation of ESCs ( Fig. 1C ; Choi et al, 2022 ). Further, we investigated quantitative PCR to identify the expression pattern of pluripotency transcription factors OCT3/4, SOX2, KLF4, and NANOG in cohesin-knockdown conditions.…”

“…The ultimate role of stem cells is defined in terms of their developmental capacity measured by their differentiation ability ( Choi et al, 2020 ; Zhang and Wang, 2008 ). The role of cohesin against ESC differentiation has previously been shown ( Choi et al, 2022 ; Khaminets et al, 2020 ; Noutsou et al, 2017 ), but whether changes in gene expression are a cause or consequence of promoting ESC self-renewal remains unclear. To define the role of cohesin in regulating ESC differentiation, we depleted the core subunit SMC3 and the kleisin subunit RAD21.…”

“…To define the role of cohesin in regulating ESC differentiation, we depleted the core subunit SMC3 and the kleisin subunit RAD21. We additionally depleted the meiotic cohesin component REC8, which was recently shown to play diverse roles in ESCs ( Choi et al, 2022 ). Depletion of each factor was conducted by treating siRNAs against SMC3, RAD21, and REC8 in ESCs.…”

“…This protein complex is composed of four core subunits, which include the structural maintenance of chromosomes (SMC) proteins SMC1A and SMC3, the kleisin protein RAD21, and the stromal antigen (SA) protein SA1/STAG1 or SA2/STAG2 ( Nasmyth and Haering, 2009 ). In addition, mammalian meiosis-specific cohesin components, which include SMC1β, RAD21L, REC8, and SA3/STAG3 ( Biswas et al, 2016 ; Choi et al, 2022 ; Hong et al, 2019 ; Ishiguro, 2019 ). Recently, Choi et al (2022) have demonstrated that the components of meiosis-specific cohesin are expressed in ESCs as well and play a role in the chromosomal organization and sister-chromatid cohesion.…”

“…In addition, mammalian meiosis-specific cohesin components, which include SMC1β, RAD21L, REC8, and SA3/STAG3 ( Biswas et al, 2016 ; Choi et al, 2022 ; Hong et al, 2019 ; Ishiguro, 2019 ). Recently, Choi et al (2022) have demonstrated that the components of meiosis-specific cohesin are expressed in ESCs as well and play a role in the chromosomal organization and sister-chromatid cohesion. Given that the cohesin complex has diverse roles in organizing chromosome dynamics and transcriptional activities related to ESC self-renewal and differentiation ( Kagey et al, 2010 ; Noutsou et al, 2017 ), it is truly positioned as a multi-functional complex that controls various cellular activities.…”