DNA methylation stabilizes X chromosome inactivation in eutherians but not in marsupials: evidence for multistep maintenance of mammalian X dosage compensation

摘要: Abstract In marsupials and eutherian mammals, X chromosome dosage compensation is achieved by inactivating one in female cells; however, marsupials, the inactive chromosomes always paternal, some genes on are partially expressed. To define role of DNA methylation maintenance inactivity, we examined loci for glucose-6-phosphate dehydrogenase hypoxanthine phosphoribosyltransferase a North American marsupial, opossum Didelphis virginiana, using genomic hybridization probes cloned from this species. We find that these marsupial like their counterparts, with respect to sex differences nuclease-insensitive (nonregulatory) chromatin. However, nuclease-hypersensitive (regulatory) chromatin locus, gene differs those eutherians, as 5' cluster CpG dinucleotides hypomethylated paternal well maternal gene. Despite hypomethylation cluster, allele, identified an enzyme variant, at best expressed; therefore, factors other than responsible repression. In light results, it seems "lock in" process initiated such factors. Because similarities between trophectoderm derivatives propose timing developmental events--rather basic mechanisms inactivation--account features differ among mammals.