Wisconsin researchers describe how d...( MADISON - Researchers at the Univers...)

MADISON - Researchers at the University of Wisconsin School of Medicine and Public Health (SMPH) are wagging a finger at currently held notions about the way digits are formed.

Studying the embryonic chick foot, the developmental biologists have come up with a model that explains how digits grow and why each digit is different from the others.

As reported in the Proceedings of the National Academy of Sciences Online Early Edition the week of March 10-14, 2008, the scientists found that the development and fate of each digit depends on a surprisingly dynamic process in unanticipated locations and involving unexpected players.

The UW-Madison team showed that growth begins in a portion of the developing digit they have named the phalanx-forming region (PFR). They illustrated that phalanges, structures that later become finger or toe bones, arise not from cartilage cells but from mesenchymal cells. And they discovered that a complex array of signals from a variety of genes at different times combine to form each phalanx.

Though the research was done on chick digits, it may have implications for humans born with a genetic condition known as bradydactyly, or stubby fingers and toes. The work was undertaken in the laboratory of John Fallon, the Harland Winfield Mossman Professor of Anatomy at the SMPH, who for years has sought to understand how cell fate is determined and patterning-of digits, teeth and feathers-is achieved during embryonic development.

In birds and mammals, digits arise in the mitten-shaped autopod, or developing foot, which consists of two alternating regions. The digital rays, made up of cartilage and mesenchyme, become the phalanges in the adult chicken's toes. These alternate with the interdigits, also consisting of mesenchymal tissue, which fill the space between the digit rays and eventually regress.

Scientists know that the gene Sonic Hedgehog (SHH) plays an important role in determi
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