Dad's genes build placenta: study

Though placenta connects the foetus and mother, scientists have found that the organ grows according to blueprints from the father.
Cornell University researchers found that the genes in a foetus that come from the father dominate in building the foetal side of the placenta.
While genes work in pairs: one from each parent, about 1 per cent 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.

To determine the genes that 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.

The study was able to identify the parent-of-origin for 7,000 genes. Of those genes, transcriptome data from placental tissue found that 93 genes were imprinted.
While only 15 of the 40 known imprinted human genes were identified in this set, their expression bias was identical to that of humans, indicating a highly conserved function for these genes between the horse family and humans, according to Cornell Chronicle.

A majority of the imprinted candidates were paternally expressed, and this expression bias was lost when the transcriptomes of foetal tissues were examined.
At the same time, as in mice, paternally imprinted genes heavily regulate placental development in these animals.
"Mouse experiments showed that if all DNA comes from the mother, the embryo grows quite well, but not the placenta, suggesting some degree of sex-based division of labour between programming the placenta and the embryo," said Wang.
"Our results confirm what these past findings suggested," Wang said.
The study was published in the Proceedings of the National Academy of Sciences.