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Evolution of Vertebrate Limb Morphology
Author(s) -
Tabin Clifford James
Publication year - 2013
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.27.1_supplement.74.3
Subject(s) - biology , numerical digit , vertebrate , anatomy , forelimb , allometry , tetrapod (structure) , primordium , femur , tibia , skeleton (computer programming) , evolutionary biology , morphology (biology) , limb development , zoology , genetics , ecology , gene , paleontology , arithmetic , mathematics
The vertebrate limb is an extraordinarily flexible structure that has evolved to accomplish a wide range of tasks in different taxa, from the grasping human hand, to the wing of the bat, the digging limb of the mole or the running leg of the horse. To understand the developmental basis for such diversity, we are focusing on the diverged morphology of the hindlimbs of jerboas, bipedal Asian rodents closely related to mice. These hindlimbs show a number of derived characteristics, including greatly increased size, altered allometric growth of individual elements (such as the metatarsals which are extended to a length similar to that of the femur or tibia); fusion of elements, and reduction in number of digits. We have found that changes in relative growth of the skeletal elements are achieved, to a large extent, by modulating the size of the individual hypertrophic cells in the developing growth plate, a multi‐phasic process involving cell swelling as well as proportional cell growth. It is the final phase of proportional mass increase, an IGF1‐dependent step, that appears to be modulated evolutionarily as skeletal element size is varied. Decrease in digit number has also been investigated in these animals. The normal set of five digit primordia appear to be specified in the jerboa hindlimbs as they are in the mouse. However, the lateral digits are lost through an expansion of cell death, regulated by Msx2 and Bmp4. A similar mechanism appears to have been used in the evolution of the single central digit of the horse.