Aberrant patterns of X chromosome inactivation in bovine clones.
In mammals, epigenetic marks on the X chromosomes are involved in dosage compensation. Specifically, they are required for X chromosome inactivation (XCI), the random transcriptional silencing of one of the two X chromosomes in female cells during late blastocyst development. During natural reproduction, both X chromosomes are active in the female zygote. In somatic-cell cloning, however, the cloned embryos receive one active (Xa) and one inactive (Xi) X chromosome from the donor cells. Patterns of XCIhave been reported normal in cloned mice, but have yet to be investigated in other species. We examined allele-specific expression of the X-linked monoamine oxidase type A (MAOA) gene and the expression of nine additional X-linked genes in nine cloned XX calves. We found aberrant expression patterns in nine of ten X-linked genes and hypomethylation of Xist in organs of deceased clones. Analysis of MAOA expression in bovine placentae from natural reproduction revealed imprinted XCI with preferential inactivation of the paternal X chromosome. In contrast, we found random XCI in placentae of the deceased clones but completely skewed XCI in that of live clones. Thus, incomplete nuclear reprogramming may generate abnormal epigenetic marks on the X chromosomes of cloned cattle, affecting both random and imprinted XCI.[1]References
- Aberrant patterns of X chromosome inactivation in bovine clones. Xue, F., Tian, X.C., Du, F., Kubota, C., Taneja, M., Dinnyes, A., Dai, Y., Levine, H., Pereira, L.V., Yang, X. Nat. Genet. (2002) [Pubmed]
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