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General Comment |
NCBI Summary:
This gene encodes the homolog of the Drosophila melanogaster Nipped-B gene product and fungal Scc2-type sister chromatid cohesion proteins. The Drosophila protein facilitates enhancer-promoter communication of remote enhancers and plays a role in developmental regulation. It is also homologous to a family of chromosomal adherins with broad roles in sister chromatid cohesion, chromosome condensation, and DNA repair. The human protein has a bipartite nuclear targeting sequence and a putative HEAT repeat. Condensins, cohesins and other complexes with chromosome-related functions also contain HEAT repeats. Mutations in this gene result in Cornelia de Lange syndrome, a disorder characterized by dysmorphic facial features, growth delay, limb reduction defects, and mental retardation. Two transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Jul 2008]
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Comment |
Localisation of the SMC loading complex Nipbl/Mau2 during mammalian meiotic prophase I. Visnes T 2013 et al.
Evidence from lower eukaryotes suggests that the chromosomal associations of all the structural maintenance of chromosome (SMC) complexes, cohesin, condensin and Smc5/6, are influenced by the Nipbl/Mau2 heterodimer. Whether this function is conserved in mammals is currently not known. During mammalian meiosis, very different localisation patterns have been reported for the SMC complexes, and the localisation of Nipbl/Mau2 has just recently started to be investigated. Here, we show that Nipbl/Mau2 binds on chromosomal axes from zygotene to mid-pachytene in germ cells of both sexes. In spermatocytes, Nipbl/Mau2 then relocalises to chromocenters, whereas in oocytes it remains bound to chromosomal axes throughout prophase to dictyate arrest. The localisation pattern of Nipbl/Mau2, together with those seen for cohesin, condensin and Smc5/6 subunits, is consistent with a role as a loading factor for cohesin and condensin I, but not for Smc5/6. We also demonstrate that Nipbl/Mau2 localises next to Rad51 and ?H2AX foci. NIPBL gene deficiencies are associated with the Cornelia de Lange syndrome in humans, and we find that haploinsufficiency of the orthologous mouse gene results in an altered distribution of double-strand breaks marked by ?H2AX during prophase I. However, this is insufficient to result in major meiotic malfunctions, and the chromosomal associations of the synaptonemal complex proteins and the three SMC complexes appear cytologically indistinguishable in wild-type and Nipbl (+/-) spermatocytes.
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Cohesion loading factor Nipbl localizes to chromosome axes during mammalian meiotic prophase. [Kuleszewicz K 2013 et al.
BACKGROUND
Sister chromatid cohesion mediated by the cohesin complex is essential for accurate chromosome segregation during mitosis and meiosis. Loading of cohesin onto chromosomes is dependent on another protein complex called kollerin, containing Nipbl/Scc2 and Mau2/Scc4. Nipbl is an evolutionarily conserved large protein whose haploinsufficiency in humans causes a developmental disorder called Cornelia de Lange syndrome. Although the function of Nipbl homologues for chromosome cohesion in meiotic cells of non-vertebrate models has been elucidated, Nipbl has not been characterized so far in mammalian spermatocytes or oocytes.
FINDINGS
Here we describe our analyses on the expression and localization of Nipbl in nuclei of mouse spermatocytes and oocytes at different stages of meiotic prophase. In both spermatocytes and oocytes we found that Nipbl is associated with the axial/lateral element of the synaptonemal complex (AE/LE) to which cohesin also localizes. Interestingly, Nipbl in spermatocytes, but not in oocytes, dissociates from the AE/LE at mid-pachytene stage coincident with completion of DNA double-strand break repair.
CONCLUSIONS
Our data propose that cohesin loading activity is maintained during early stages of meiotic prophase in mammalian spermatocytes and oocytes.
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