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A step on the road from egg laying to placental

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Author Topic:   A step on the road from egg laying to placental
jar
Member (Idle past 420 days)
Posts: 34026
From: Texas!!
Joined: 04-20-2004

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Message 1 of 4 (268231)
12-12-2005 2:23 PM

Retrotransposon gene codes for placenta
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Yet another indication of when the change from egg laying to egg bearing happened and the genetic mutations that lead to the placental animals.
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{Fixed topic title (changed "stepon" to "step on"). - Adminnemooseus}
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This message has been edited by Adminnemooseus, 12-16-2005 05:58 PM
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ReverendDG
Member (Idle past 4136 days)
Posts: 1119
From: Topeka,kansas
Joined: 06-06-2005

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Message 2 of 4 (269902)
12-16-2005 4:40 AM

that still doesn't explain..
The Platypus
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Mammuthus
Member (Idle past 6501 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002

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Message 3 of 4 (269906)
12-16-2005 4:56 AM 		Reply to: Message 1 by jar
12-12-2005 2:23 PM

This is an interesting find in that they actually compared placentals and marsupials. There are other examples of transposable elements and placental development which illustrate a wonderful case of convergent evolution.
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Two endogenous retroviral envelope genes are required for placental formation in humans and non-human primates (Syncytin-1 and 2) which are a HERV-W and HERV-FRD envelope gene respectively. Mice (and other mammals) don't have these HERVs..however, distantly related ERV envelope genes perform exactly the same function in mice (syncytin A and B).
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It is not so surprising as envelope genes are highly fusiogenic and placental formation requires synctiotrophoblast fusion. But it is a nice example of beneficial mutations caused by retroelements that can cause huge evolutionary events.
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References
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Dupressoir A, Marceau G, Vernochet C, Benit L, Kanellopoulos C, Sapin V, Heidmann T. Related Articles, Links
Syncytin-A and syncytin-B, two fusogenic placenta-specific murine envelope genes of retroviral origin conserved in Muridae.
Proc Natl Acad Sci U S A. 2005 Jan 18;102(3):725-30. Epub 2005 Jan 11.
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Blaise S, de Parseval N, Benit L, Heidmann T. Related Articles, Links
Genomewide screening for fusogenic human endogenous retrovirus envelopes identifies syncytin 2, a gene conserved on primate evolution.
Proc Natl Acad Sci U S A. 2003 Oct 28;100(22):13013-8. Epub 2003 Oct 13.
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Nuggin
Member (Idle past 2519 days)
Posts: 2965
From: Los Angeles, CA USA
Joined: 08-09-2005

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Message 4 of 4 (270130)
12-16-2005 5:47 PM 		Reply to: Message 2 by ReverendDG
12-16-2005 4:40 AM

Re: that still doesn't explain..
that still doesn't explain the platypus
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Sadly, almost nothing does.
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