Regulation and function of Spalt proteins during animal development.

The genes of the spalt (sal) family play fundamental roles during animal development. The two members of this family in Drosophila, spalt (sal) and spalt-related (salr) encode Zn-finger transcription factors that link the Decapentaplegic (Dpp)/BMP signalling pathway to the patterning of the wing. They are regulated by the Dpp pathway in the wing disc, and they were shown to mediate some of the morphogenetic activities of the Dpp/BMP4 secreted ligand. The sal genes were initially found by virtue of mutations that produce homeotic transformations in the head and tail of the Drosophila embryo. Since then, a number of other requirements have been associated to these genes in Drosophila, including morphogenesis of the respiratory system, cell fate specification of sensory organs and the differentiation of several photoreceptor cells, among others. Vertebrate sal orthologues (spalt-like/sall) have also important developmental roles during neural development and organogenesis, and at least two human sall genes are linked to the genetic diseases Townes Brocks Syndrome (TBS; SALL1 ) and Okihiro Syndrome (OS; SALL4 ). In this review, we will summarize the main characteristics of the sall genes and proteins, pointing out to the similarities in their developmental roles during Drosophila and vertebrate development.