Houlard Martin, Godwin Jonathan, Metson Jean, Lee Jibak, Hirano Tatsuya, Nasmyth Kim
Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
Laboratory of Developmental Biotechnology, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan.
Nat Cell Biol. 2015 Jun;17(6):771-81. doi: 10.1038/ncb3167. Epub 2015 May 11.
In addition to inter-chromatid cohesion, mitotic and meiotic chromatids must have three physical properties: compaction into 'threads' roughly co-linear with their DNA sequence, intra-chromatid cohesion determining their rigidity, and a mechanism to promote sister chromatid disentanglement. A fundamental issue in chromosome biology is whether a single molecular process accounts for all three features. There is universal agreement that a pair of Smc-kleisin complexes called condensin I and II facilitate sister chromatid disentanglement, but whether they also confer thread formation or longitudinal rigidity is either controversial or has never been directly addressed respectively. We show here that condensin II (beta-kleisin) has an essential role in all three processes during meiosis I in mouse oocytes and that its function overlaps with that of condensin I (gamma-kleisin), which is otherwise redundant. Pre-assembled meiotic bivalents unravel when condensin is inactivated by TEV cleavage, proving that it actually holds chromatin fibres together.
除了染色单体内的黏连外，有丝分裂和减数分裂的染色单体还必须具备三种物理特性：压缩成大致与其DNA序列共线的“细丝”、决定其刚性的染色单体内黏连，以及促进姐妹染色单体解缠结的机制。染色体生物学中的一个基本问题是，单一分子过程是否能解释这三种特性。人们普遍认为，一对名为凝聚素I和凝聚素II的Smc- kleisin复合物有助于姐妹染色单体解缠结，但它们是否也赋予细丝形成或纵向刚性，要么存在争议，要么从未分别直接探讨过。我们在此表明，凝聚素II（β- kleisin）在小鼠卵母细胞减数分裂I的所有三个过程中都起着至关重要的作用，并且其功能与凝聚素I（γ- kleisin）的功能重叠，否则凝聚素I是多余的。当凝聚素通过TEV切割失活时，预先组装好的减数分裂二价体就会解开，这证明它实际上将染色质纤维维系在一起。
