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Going To Extremities
By Sean Henahan, Access Excellence
 Ann
Arbor, MI (November 6, 1997)- Is the measure of a man related to his
glove size? It seems there may be some genetic basis for the folk belief
in the metric symmetry of digits and other extremities.
Genes in the Hox
family are known to be essential for controlling limb development in a
wide range of species. Now an international research team reports that
a particular subset of Hox genes appears to control the development of
digits as well as external genitalia.
Hox genes allow an embryo to develop different structures along the
length of the body. In the mouse, for example, certain Hox genes are active
toward the head end of the embryo, causing the neck to acquire cervical
vertebrae and other characteristic structures. Others are active further
along, orchestrating the production of thoracic vertebrae and other chest
features.
Researchers at the University of Geneva in Switzerland and the University
of Michigan Medical School, Ann Arbor, Michigan, bred mice unable to express
the Hox genes for limb development. The mice developed without digits or
penises, suggesting that the involvement of Hox genes concerns the development
of apical structures -- "morphogenetic end-points of the body", or, extremities
in plain English.
"Perhaps the origin of the penis correlates to the introduction or improvement
of the digits," speculates Denis Duboule.
The researchers speculate that the development of external genitalia
along with digits could be connected with the transition from aquatic to
terrestrial life. The shared genetic developmental regulation of these
structures suggests that they might have evolved in a coordinated way.
The research appears in the Novemeber 6, 1997 issue of Nature.
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