Of Hinnys and Mules

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Science  28 Jun 2013:
Vol. 340, Issue 6140, pp. 1500
DOI: 10.1126/science.340.6140.1500-b

Imprinting—the silencing of genes due to the methylation of specific DNA sequences coming from one parent—is known to play a crucial role in the development of the placenta in mammals. The offspring of matings between horses and donkeys are generally viable, but sterile. However, because of genetic differences between the species, estimated via RNA sequencing, Wang et al. were able to assess transcription differences and to identify equid-specific imprinted genes in the chorionic girdle that do not appear to be due to their hybrid status. Of 40 known imprinted genes in humans and/or mice, only 15 were imprinted in the equine offspring. They also identified 93 imprinted genes, including 78 not previously described, that showed distribution across the genome and not in clusters, as had previously been observed for imprinted genes. Furthermore, imprinted genes appear to show specific differences between equids versus humans and mice, suggesting that equine hybrids may provide information on the evolutionary origins and maintenance of genomic imprinting.


Proc. Natl. Acad. Sci. U.S.A. 110, 10.1073/pnas.1308998110 (2013).

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