Cohesin SMC1β protects telomeres in meiocytes

Meiosis-specific mammalian cohesin SMC1 beta is required for complete sister chromatid cohesion and proper axes/loop structure of axial elements (AEs) and synaptonemal complexes (SCs). During prophase I, telomeres attach to the nuclear envelope (NE), but in Smc1 beta(-/-) meiocytes, one fifth of their telomeres fail to attach. This study reveals that SMC1 beta serves a specific role at telomeres, which is independent of its role in determining AE/SC length and loop extension. SMC1 beta is necessary to prevent telomere shortening, and SMC3, present in all known cohesin complexes, properly localizes to telomeres only if SMC1 beta is present. Very prominently, telomeres in Smc1 beta(-/-) spermatocytes and oocytes loose their structural integrity and suffer a range of abnormalities. These include disconnection from SCs and formation of large telomeric protein-DNA extensions, extended telomere bridges between SCs, ring-like chromosomes, intra-chromosomal telomeric repeats, and a reduction of SUN1 foci in the NE. We suggest that a telomere structure protected from DNA rearrangements depends on SMC1 beta.