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“Drinkable” placenta nourishes marsupial young, say researchers at Stanford, Australia

I will try to refrain from using too many exclamation points, but my latest article was so! much! fun! to write. (There. Now I've got it out of my system. I think.) In short, I got to do a deep dive (metaphorically of course) into the soft, warm, cozy depths of the pouch of one of the tiniest, and cutest of Australia's marsupials thanks to geneticist Julie Baker, PhD, and graduate student Michael Guernsey. They recently collaborated with Australian researcher Marilyn Renfree, PhD, to investigate the unique development of the wallaby, which trades off an extended pregnancy for a long period of lactation. They published their results today in eLife.

From our release:

Guernsey and Baker studied the placenta of the tammar wallaby, which is native to Australia. To the marsupially naïve, it resembles a tiny kangaroo. Males weigh no more than 20 pounds and stand about 18 inches high. It forages hoppily by night. The tammar wallaby has a pregnancy that lasts a mere 26.5 days, after which the young climb into the pouch and nurse for the next 300 to 350 days as they complete their development...

For decades, researchers assumed that this premature eviction from the womb left little or no role for the placenta, which in most mammals tightly links the physiological processes of the mother and the fetus to support the fetus's many stages of development. These mammals are called eutherian mammals to distinguish them from the evolutionarily distant marsupials. In the past decade or so, however, it has become apparent that marsupials do sport their own, rudimentary version of this important organ.

Baker and Guernsey's research further confirmed the existence of the elusive marsupial placenta. But they also discovered something new, and uber fascinating: Many genes expressed by the eutherian placenta in the later stages of fetal development are instead produced in the wallaby's mammary gland and are delivered to the baby in the milk.

As Baker described:

This research basically shows that the placenta, while really different-looking in the marsupial, has many of the functions of the eutherian. Each animal has come up with their own unique strategies for delivering the functions of the placenta that takes into account where they live, how many offspring they have and what they eat, for example. But the actual function is very well-conserved.

As she further confided to me during a phone call, "We just think the placental is really cool."

It is, I agree! [Whoops.] As are wallabies! [OK, that was the last one.]

Previously: Mouse placental cells contain dozens, even hundreds of copies of genes key for pregnancy, NIH puts focus on the placenta, the "fascinating" and "least understood" organ and Species-specific differences among placentas due to long-ago viral infection, say Stanford researchers
Photo by MB Renfree

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