Thelma B K, Tewari R, Juyal R C, Rao S R
Department of Genetics, University of Delhi, India.
Cytogenet Cell Genet. 1991;56(2):87-90. doi: 10.1159/000133056.
Five types of X chromosomes with different amounts of heterochromatin have been observed in Nesokia indica, the Indian mole rat. They have been found in both mosaic and nonmosaic individuals. The influence, if any, of heterochromatin on the kinetics of X-chromosome DNA replication was evaluated in bone marrow cells and peripheral blood lymphocytes of Nesokia females with variant X chromosomes. In bone marrow cells of nonmosaic females a random X-chromosome inactivation (XCI) pattern was observed, except when there was a total loss of heterochromatin from the variant X chromosome, resulting in predominantly early replication. A nonrandom pattern was observed, however, in blood and bone marrow cells of all individuals with mosaic genotypes. In these females the X chromosome with the lesser amount of heterochromatin was predominantly the active one. The amount of heterochromatin per se or, more likely, specific sequences contained in the heterochromatic region seem to influence the XCI pattern in a cis-acting manner. The observations also seem to support a process of cell selection in individuals with variant X chromosomes.
在印度鼹形田鼠（Nesokia indica）中观察到了五种具有不同异染色质含量的X染色体。它们在嵌合体和非嵌合体个体中均有发现。在具有变异X染色体的Nesokia雌性个体的骨髓细胞和外周血淋巴细胞中，评估了异染色质对X染色体DNA复制动力学的影响（若有影响的话）。在非嵌合体雌性的骨髓细胞中，观察到随机的X染色体失活（XCI）模式，除非变异X染色体完全丧失异染色质，此时主要导致早期复制。然而，在所有具有嵌合基因型个体的血液和骨髓细胞中观察到了非随机模式。在这些雌性个体中，异染色质含量较少的X染色体主要是活跃的。异染色质本身的量，或者更有可能是异染色质区域中包含的特定序列，似乎以顺式作用方式影响XCI模式。这些观察结果似乎也支持了具有变异X染色体个体中的细胞选择过程。
