2da. Cátedra de Histología, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155 Piso 10 (C1121ABG), Ciudad Autónoma de Buenos Aires, Buenos Aires, Argentina.
Chromosome Res. 2012 Feb;20(2):293-302. doi: 10.1007/s10577-012-9273-4. Epub 2012 Jan 25.
Three xenarthrans species Chaetophractus villosus, Chaetophractus vellerosus, and Zaedyus pichiy have been used for the analysis of the structure, behavior, and immunochemical features of the XY body during pachytene. In all these species, the sex chromosomes form an XY body easily identifiable in thin sections by the special and regular packing of the chromatin fibers of the internal region of the XY body ("differential" regions) and those of the peripheral region (synaptic region). Spermatocyte spreads show a complete synapsis between the X- and the Y-axis, which lasts up to the end of pachytene. From the early pachytene substages to the late ones, the X-axis develops prominent branches, which in late pachytene span the synaptic region. Synapsis is regular as shown by SYCP1 labeling. Axial development is followed by SYCP3 labeling and in the asynaptic region of the X-axis by BRCA1. Gamma-H2AX labels exclusively the differential (asynaptic) region of the X chromosome. A single focus is labeled by MLH1 in the synaptic region. The location of this MLH1 focus spans from 0.3 to 1.6 μm from the telomere in the analyzed xenarthrans, covering approximately half of the Y-axis length. It is concluded that xenarthrans, as basal placental mammals, harbor the largest pseudoautosomal regions of presently analyzed mammals, and shows the typical features of meiotic sex chromosome inactivation (MSCI).
三种贫齿目动物（犰狳科）——鬃毛犰狳、巴西三带犰狳和毛犰狳——已被用于分析在粗线期时 XY 体的结构、行为和免疫化学特征。在所有这些物种中，性染色体形成一个 XY 体，在薄切片中很容易通过 XY 体内部区域（“差异”区域）和外围区域（联会区域）染色质纤维的特殊和规则排列来识别。精母细胞铺片显示 X 和 Y 轴之间完全联会，这种联会一直持续到粗线期结束。从早期粗线期亚期到晚期，X 轴发育出明显的分支，这些分支在晚期粗线期跨越联会区域。联会是规则的，如 SYCP1 标记所示。轴的发育随后是 SYCP3 标记，而在 X 轴的非联会区域则是 BRCA1。γ-H2AX 仅标记 X 染色体的差异（非联会）区域。在联会区域中，MLH1 标记一个单一的焦点。在分析的贫齿目动物中，这个 MLH1 焦点的位置从端粒到 0.3 到 1.6 μm 不等，大约覆盖了 Y 轴长度的一半。结论是，作为基底胎盘哺乳动物的贫齿目动物拥有目前分析的哺乳动物中最大的假常染色体区域，并显示出减数分裂性染色体失活（MSCI）的典型特征。
