Tuesday, 12 March 2013

What genes are needed to build a placenta?

Eutheria placenta shared and lineage-specific expressed genes
From Huo et al. (2012) © The Authors 2012

The chorioallantoic placenta is a defining feature of placental mammals and evolved after the split between Eutheria and Metatheria around 160 million years ago (most marsupials have a yolk sac placenta). What genes were recruited to build it? An answer based on mouse placenta is not fully satisfactory as a new study from Derek Wildman’s group confirms.

They determined which genes were highly expressed in the placenta of the African elephant. A comparison was made with similar information from human, mouse and cow placentas. Together these species cover three of the four major clades of placental mammal with the elephant representing the basal clade Afrotheria.

In an insightful analysis, the authors looked for a subset of 245 genes that when knocked out in the mouse gave abnormal placental morphology. Only 90 of these genes were expressed in all four placental types examined, although an additional 62 were shared by mouse and human.

What about me? Nine-banded armadillo (Wikimedia Commons)

The analysis did not include a member of Xenarthra by some considered basal even to Afrotheria. Perhaps this was because the genome of the nine-banded armadillo is available only as a draft sequence.

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