Berríos Soledad, Fernández-Donoso Raúl, Page Jesús, Ayarza Eliana, Capanna Ernesto, Solano Emanuela, Castiglia Riccardo
Universidad de Chile, Programa Genética.
Eur J Histochem. 2018 Feb 20;62(1):2894. doi: 10.4081/ejh.2018.2894.
The size and shape of the chromosomes, as well as the chromosomal domains that compose them, are determinants in the distribution and interaction between the bivalents within the nucleus of spermatocytes in prophase I of meiosis. Thus the nuclear architecture characteristic of the karyotype of a species can be modified by chromosomal changes such as Rb chromosomes. In this study we analysed the meiotic prophase nuclear organization of the heterozygous spermatocytes from Mus musculus domesticus 2n=26, and the synaptic configuration of the hexavalent formed by the dependent Rb chromosomes Rbs 6.16, 16.10, 10.15, 15.17 and the telocentric chromosomes 6 and 17. Spreads of 88 pachytene spermatocytes from two males were studied and in all of them five metacentric bivalents, four telocentric bivalents, one hexavalent and the XY bivalent were observed. About 48% of the hexavalents formed a chain or a ring of synapsed chromosomes, the latter closed by synapsis between the short arms of telocentric chromosomes 6 and 17. About 52% of hexavalents formed an open chain of 10 synapsed chromosomal arms belonging to 6 chromosomes. In about half of the unsynapsed hexavalents one of the telocentric chromosome short arms appears associated with the X chromosome single axis, which was otherwise normally paired with the Y chromosome. The cluster of pericentromeric heterochromatin mostly determines the hexavalent's nuclear configuration, dragging the centromeric regions and all the chromosomes towards the nuclear envelope similar to an association of five telocentric bivalents. These reiterated encounters between these chromosomes restrict the interactions with other chromosomal domains and might favour eventual rearrangements within the metacentric, telocentric or hexavalent chromosome subsets. The unsynapsed short arms of telocentric chromosomes frequently bound to the single axis of the X chromosome could further complicate the already complex segregation of hexavalent chromosomes.
染色体的大小和形状，以及构成它们的染色体结构域，是减数分裂前期I精母细胞核内二价体之间分布和相互作用的决定因素。因此，物种核型的核结构特征可因染色体变化（如Rb染色体）而改变。在本研究中，我们分析了小家鼠2n = 26杂合精母细胞的减数分裂前期核组织，以及由依赖的Rb染色体Rbs 6.16、16.10、10.15、15.17和端着丝粒染色体6和17形成的六价体的联会构型。研究了来自两只雄性的88个粗线期精母细胞的铺展，在所有细胞中均观察到5个中着丝粒二价体、4个端着丝粒二价体、1个六价体和XY二价体。约48%的六价体形成了联会染色体的链或环，后者通过端着丝粒染色体6和17短臂之间的联会而闭合。约52%的六价体形成了由属于6条染色体的10个联会染色体臂组成的开放链。在约一半未联会的六价体中，其中一个端着丝粒染色体短臂似乎与X染色体单轴相关联，否则X染色体通常与Y染色体配对。着丝粒周围异染色质的聚集主要决定了六价体的核构型，将着丝粒区域和所有染色体拖向核膜，类似于5个端着丝粒二价体的联合。这些染色体之间反复的相遇限制了与其他染色体结构域的相互作用，并可能有利于中着丝粒、端着丝粒或六价体染色体亚组内最终的重排。端着丝粒染色体未联会的短臂频繁地与X染色体单轴结合，这可能会使已经复杂的六价体染色体分离更加复杂。
