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Mice Get Re-Armed

December 9, 2014

Eva Gusnowski

The right to bear arms has long been a right afforded only to humans.  However the mouse has recently been re-armed (recent being an evolutionary relative term of course) with a full clip of bat genes. 

Okay, maybe not a full bat gene.  But a small part of one at least.

First let’s explore a couple of basics:

Homologous structures are a mainstay of evolutionary theories, from genetics to phylogeny.  The fact that all of these creatures (including us) are actually so similar to one another at the level of DNA sequences all of the way to the skeleton is strong evidence of common ancestors and of divergent evolution.

 

The regulation of gene expression is an incredibly complex and intricate process.  A few of the main players include a promoter region (found shortly before (upstream) a gene sequence and helps turn on expression), and in some cases repressor sequences (that stop/decrease expression) and enhancer sequences (that increase/direct expression).  Enhancer regions not only help turn a gene’s expression up and down, but can also allow for tissue and temporal specific gene expression.

 

How does this go together then? 

 

A study published in 2008 looked at the expression of a gene called Prx-1 in an incredibly interesting way.  Prx-1 is a gene whose protein product is involved in the regulation of bone length in mice, and its homolog (i.e. essentially the same/similar gene in other creatures) does the same in other mammals.  However, in order to shape the multitude of different lengths of forearm bones in the animal kingdom, Prx-1 gene expression is higher or lower in various creatures to make longer or shorter limbs, respectively.  In order to study the function of Prx-1 further, this group took the Prx-1 enhancer sequence from bats and inserted it in front of the Prx-1 gene in mice. 

 

                                                  Cretekos et al., 2008

You can imagine that the expression of Prx-1 in bats would be higher and longer because bats have longer forearms than mice.  What were they looking for in the transgenic mice?  You guessed it, longer forearms due to increased Prx-1 expression in the skeleton.

 

                                                Cretekos et al., 2008

Although the transgenic mice had forearms that were only on average 6% longer, implying that other regulatory elements are involved in Prx-1 function, this study suggests a strong relationship between two very different appearing mammals at the DNA level.  It also lends even more support to the theory of evolution and the successive changes in gene expression that have allowed for adaptation to flying versus skittering across a floor. 

If only the T-rex knew about the Prx-1 gene and could’ve done this experiment themselves.  Unstoppable.

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