Fig. 9. Snail family of proteins play an essential role in neuroblast development. Many pro-neural genes control the expression of snail and worniu in neuroblasts. Snail and Worniu, and to a lesser extent Escargot, normally function to regulate the asymmetry and cell division of neuroblasts by controlling the expression of inscuteable and string, respectively. The correct expression of these two genes is required for proper segregation of Prospero into GMC, where Prospero functions as a crucial factor for cell fate determination. The arrows indicate genetic hierarchy, not necessarily direct regulation. The Snail family of proteins likely function as repressors. Thus, the regulation of inscuteable and string may be through the repression of another repressor, leading to gene activation. It is also possible that the Snail family of proteins can directly activate the expression of these two genes.
