How some mammals pause their pregnancies

Biochemical reasons for lag times between conception and pregnancy in mice became clearer in a recent study

Date: February 10, 2020

Source: University of Washington Health Sciences/UW Medicine

How do some mammals postpone the development of their embryos to await better conditions for having offspring? A recent study at the UW Medicine Institute for Stem Cell and Regenerative Medicine explored this reproductive enigma, which can occur in more than 130 species of mammals as well as in some marsupials.

The study was study led by Abdiasis Hussein, a graduate student in the lab of Hannele Ruohola-Baker, UW professor of biochemistry and associate director of UW Medicine's Institute for Stem Cell and Regenerative Medicine. The findings were reported in Developmental Cell, a Cell Press scientific journal.

The results not only advance the understanding of delayed embryo implantation, but also suggest how some otherwise rapidly dividing cells, such as those in tumors, become quiescent.

In the suspended state of pregnancy called embryonic diapause, an early-stage embryo refrains from implanting in the mother's uterus, where it could be nourished to grow into a baby. Instead, like a seed, the embryo remains dormant until certain molecular regulators prod it to germinate.

Diapause, or delayed implantation, is a biological strategy for waiting out conditions unfavorable to sustaining newborns, such as lack of food, insufficient maternal fat stores, or older siblings who haven't been weaned.

Bears, armadillos, seals, and some otters, badgers and other weasel-like animals undergo seasonal diapause, as a regular part of their reproductive cycles.

Many types of bears, for example, breed in the late spring or early summer. The female then voraciously hunts for food. Only when the female bear has sufficient body fat and weight will one or more of her embryos implant months later, after she retreats to her den. Any cubs would be born in late winter.

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