Scientists find 'redesigned hammer' that forged evolution of pregnancy in mammals

Sep 18, 2008
Old (A) and new (B) models for the role in evolution of regulatory proteins: "tools" may be redesigned (B) as well as reapportioned (A). Credit: Wagner/Lynch

Yale researchers have shown that the origin and evolution of the placenta and uterus in mammals is associated with evolutionary changes in a single regulatory protein, according to a report in Proceedings of the National Academy of Sciences.

"Many past studies have shown that genes are regulated and altered by changes within their own structures. This is the first work suggesting that the evolution of transcription factors — separate regulatory proteins — may play an active role in the origin and evolution of structural innovations like the placenta and uterus," said senior author Gunter Wagner, the Alison Richard Professor of Ecology & Evolutionary Biology at Yale.

Pregnancy is a biologically unusual situation where one organism lives and develops inside another that is genetically different. Ordinarily, the immune system identifies and destroys the dissimilar tissue as if it were a parasite. But in some early mammals, changes 'turned down' the immune system, allowing the developing embryo to grow and thrive unchallenged by the maternal immune response.

With the evolution of the uterus and placenta, it became possible for mammals to protect their growing young and to ensure they were not exposed to an unpredictable environment, like their egg-laying relatives. This study identified one of the genetic switches that tempered the immune system and allowed formation of the placenta and internal development of young.

By analyzing DNA from many species of mammals, including resurrecting genes from the extinct ancestors of mammals, the researchers found that a crucial regulatory link in the evolution of pregnancy involved the altered function of a transcription factor protein, HoxA-11.

The specific change they found in HoxA-11 is present in all known placental mammals — from elephants, the most primitive lineage with a placenta, to humans — but does not exist in marsupials, like opossums or wallabies, where there is a brief and rudimentary pregnancy followed by development of the offspring outside the mother, or in egg-laying mammals like the platypus.

The textbook story is that regulatory proteins, like HoxA-11, are ancient, universal and unchanging tools, and that new functions arise by using an existing tool from the gene regulatory 'toolbox' in a new or different place.

According to Yale graduate student Vincent Lynch, lead author of the study, "We are writing a different chapter. In this case the function of a major regulatory tool was altered — it is like we found a redesigned hammer."

Citation: Proc. Natl. Acad. Sci. (early online September 17, 2008)

Source: Yale University

Explore further: Research to the rescue: Fishing for rhinos with tekken

add to favorites email to friend print save as pdf

Related Stories

Evolution: The genetic connivances of digits and genitals

Nov 20, 2014

During the development of mammals, the growth and organization of digits are orchestrated by Hox genes, which are activated very early in precise regions of the embryo. These "architect genes" are themselves regulated by ...

Life on Earth still favours evolution over creationism

Sep 11, 2014

Charles Darwin's Theory of Evolution, first published in 1859, offered a bold new explanation for how animals and plants diversified and still serves as the foundation underpinning all medical and biological ...

Recommended for you

Salish Sea seagull populations halved since 1980s

41 minutes ago

The number of seagulls in the Strait of Georgia is down by 50 per cent from the 1980s and University of British Columbia researchers say the decline reflects changes in the availability of food.

Cultivation of microalgae via an innovative technology

51 minutes ago

Preliminary laboratory scale studies have shown consistent biomass production and weekly a thick microalgal biofilm could be harvested. A new and innovative harvesting device has been developed for ALGADISK able to directly ...

100,000 bird samples online

1 hour ago

The Natural History Museum (NHM) in Oslo has a bird collection of international size. It is now available online.

Banksias differ on resilience to climate change

2 hours ago

Research into the germination requirements of four Banksia species (Proteaceae) endemic to the South West Australian Floristic Region (SWAFR) has found certain species may be more vulnerable to climate change ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.