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New bird digit study supports "frame shift"



From: Ben Creisler
bh480@scn.org

A new online paper:

Zhe Wang, Rebecca L. Young, Huiling Xue & Günter P. 
Wagner (2011) 
Transcriptomic analysis of avian digits reveals conserved 
and derived digit identities in birds.
Nature (advance online publication)
doi:10.1038/nature10391 
http://www.nature.com/nature/journal/vaop/ncurrent/full/na
ture10391.html

Morphological characters are the result of developmental 
gene expression. The identity of a character is 
ultimately grounded in the gene regulatory network 
directing development and thus whole-genome gene 
expression data can provide evidence about character 
identity. This approach has been successfully used to 
assess cell-type identity. Here we use transcriptomic 
data to address a long-standing uncertainty in 
evolutionary biology, the identity of avian wing digits. 
Embryological evidence clearly identifies the three wing 
digits as developing from digit positions 2, 3 and 4 
(ref. 6), whereas palaeontological data suggest that they 
are digits I, II and III. We compare the transcriptomes 
of the wing and foot digits and find a strong signal that 
unites the first wing digit with the first foot digit, 
even though the first wing digit develops from 
embryological position 2. Interestingly, our 
transcriptomic data of the posterior digits show a higher 
degree of differentiation among forelimb digits compared 
with hindlimb digits. These data show that in the stem 
lineage of birds the first digit underwent a 
translocation from digit position 1 to position 2, and 
further indicate that the posterior wing digits have 
unique identities contrary to any model of avian digit 
identity proposed so far.

News story:
http://www.physorg.com/news/2011-09-mystery-bird-
digit.html

======
Note that this analysis is different from the one 
recently posted in Nature Communications, which seemed to 
indicate that there is no ?frame shift? in digit position.

http://www.nature.com/ncomms/journal/v2/n8/full/ncomms1437
.html
http://www.cosmosmagazine.com/news/4603/birds-have-
dinosaur-digits-1-2-and-3