Dad's genes build placentas, study shows

Though placentas support the fetus and mother, it turns out that the organ grows according to blueprints from dad, says new Cornell research. The study, published in the Proceedings of the National Academy of Sciences in June, shows that the genes in a fetus that come from the father dominate in building the fetal side of the placenta.

Genes work in pairs: one from each parent. But about 1 percent of mammalian genes choose sides, a phenomenon called genomic imprinting. Imprinted genes use molecules that bind to DNA (epigenetic tags) to quiet one half and let the other lead. In the study, the researchers discovered 78 new imprinted genes using horse-donkey hybrids.

"This is the first study to offer an unbiased profile of novel imprinted genes in a mammal other than mice," said lead author Xu Wang, a postdoctoral associate in the laboratory of Andrew Clark, professor of molecular biology and genetics and the study's senior author.

Using mouse studies, only about 100 genes with imprinted expression had been identified. To determine whether other genes exhibit imprinted expression, Wang and colleagues sequenced all of the expressed genes (the transcriptome) of hinnies (whose mothers are donkeys; fathers horses) and mules (whose mothers are horses; fathers donkeys) and looked for parent-of-origin differences.