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Remember this post from a couple of weeks ago? It was quite popular on tagging sites like Digg, Reddit and Stumbleupon. It was about endogenous retroviruses and their role in the evolution of placenta (which made the evolution of other mammalian traits possible).

Now, there is a new study in sheep, on this same topic, and it looks very good at first glance:

Researchers Discover That Sheep Need Retroviruses For Reproduction:

A team of scientists from Texas A&M University and The University of Glasgow Veterinary School in Scotland has discovered that naturally occurring endogenous retroviruses are required for pregnancy in sheep.

In particular, a class of endogenous retroviruses, known as endogenous retroviruses related to Jaagsiekte sheep retrovirus or enJSRVs, are critical during the early phase of pregnancy when the placenta begins to develop.

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The idea that endogenous retroviruses are important for reproduction in mammals has been around for about 30 years, Spencer said. Studies in cultured cells have shown that a protein of a human endogenous retrovirus might have a role in development of the human placenta.

The team blocked expression of the envelope of the enJSRVs using morpholino antisense oligonucleotides, which inhibit translation of specific messenger RNA. When production of the envelope protein was blocked in the early placenta, the growth of the placenta was reduced and a certain cell type, termed giant binucleate cells, did not develop.

The result was that embryos could not implant and the sheep miscarried, Spencer said.