Evolutionary origin of chromatin remodeling for dosage compensation: Lessons from epigenetic modifications of X chromosomes in germ cells of Drosophila, C.elegans and Mammals

摘要

Epigenetic modifications of entire X chromosome(s) are adapted in many animals to keep balance of gene dose difference between sexes possessing different number of sex chromosomes required for sex determination. Different animals have adapted different mechanisms for epigenetic regulation of X chromosomal expression depending on ‘demasculinization’ of the X chromosome. The epigenetic programming for dosage compensation in Drosophila is to hyperactivate the male X chromosome by histone H4 modification. In Caenorhabditis elegans, both X chromosomal histones of hermaphrodite are methylated for down regulation of X linked gene expression. Mammals have developed a system of epigenetic modification for both upregulation and repression of X chromosomal genes for dosage compensation. In recent years, epigenetic modifications that occur during male meiosis are characterized with special attention on events that define meiotic sex chromosome inactivation. As data accumulate, noval features of dosage compensation processes of different animals are also gaining attention. This review highlights the crucial roles of germline X chromosomal organization, that are potentially relevant to epigenetic modulation of somatic dosage compensation in the three animals.