London: A study has been able to uncover the mystery of the three different digits on a bird, whether they developed as a thumb with index and middle fingers, or the index, middle and ring fingers.
Yale scientists now have a good handle on how these developmental changes are orchestrated in the embryo.
The stem cells in birds that normally produce the first digit die off during early stages of embryonic development, while cells programmed to manufacture the index unit give rise instead to a thumb-like appendage.
In five-digit vertebrates, the thumb comes from the precursor stem cells labelled pa. While birds have a digit that looks like a thumb, pa precursor cells die off during development and never produce a digit in adults.
As a result, scientists have wondered whether precursor cells in pb can make a thumb.
Yale scientists have completed a genomic analysis of birds that reveals the answer, and it is a big “yes” — even though the first bird digit develops where the index finger on a five-finger vertebrae should be.
The authors of the study are Zhe Wang, Rebecca L. Young, Huiling Xue, and Gunter P. Wagner from the Department of Ecology and Evolutionary Biology.
The findings have been published online September 4 in the journal Nature.