PAX GENES AND ORGANOGENESIS

Pax genes are a family of developmental control genes that encode nucl ear transcription factors. They are characterized by the presence of t he paired domain, a conserved amino acid motif with DNA-binding activi ty. Originally, pal red-box-containing genes were detected in Drosophi la melanogaster, where they exert multiple functions during embryogene sis. In vertebrates, Pax genes are also involved in embryogenesis. Mut ations in four out of nine characterized Pax genes have been associate d with either congenital human diseases such as Waardenburg syndrome ( PAX3), Aniridia (PAX6), Peter's anomaly (PAX6), renal coloboma syndrom e (PAX2) or spontaneous mouse mutants (undulated (Pax1); Splotch (Pax3 ), Small eye (Pax6), Pax2(1Neu)), which all show defects in developmen t. Recently, analysis of spontaneous and transgenic mouse mutants has revealed that vertebrate Pax genes are key regulators during organogen esis of kidney, eye, ear, nose, limb muscles, vertebral column and bra in. Like their Drosophila counterparts, vertebrate Pax genes are invol ved in pattern formation during embryogenesis, possibly by determining the time and place of organ initiation or morphogenesis. For most tis sues, however, the nature of the primary developmental action of Pax t ranscription factors remains to be elucidated. One predominant theme i s signal transduction during tissue interactions, which may lead to a position-specific regulation of cell proliferation.