Snail Gene Family Research Articles

Mgm 1, the earliest sex-specific germline marker in Drosophila, reflects expression of the gene esg in male stem cells.

The pathway that controls sex in Drosophila has been well characterized. The elements of this genetic hierarchy act cell-autonomously in somatic cells. We have previously shown that the sex of germ cells is determined by a different mechanism and that somatic and autonomously acting elements interact to control the choice between spermatogenesis and oogenesis. A target for both types of signals is the enhancer-trap mgm1, which monitors male-specific gene expression in germ cells. Here we report that mgm1 reflects the expression of escargot (esg), a member of the snail gene family, which are transcription factors with zink finger motifs. Genes of this family partially redundantly control a number of processes involving cell fate choices. The regulation of gene expression in germ cells by sex-specific esg enhancers is already seen in embryos. Therefore, autonomous and non-autonomous sex-specific factors that participate in germline sex determination are already present at this early stage. esg is expressed in the male gonad, both in somatic cells and in germline stem cells. We show that esg expression in the male germline is not required for proper sex determination and spermatogenesis, as functional sperm is differentiated by mutant germ cells in wild type hosts. However, somatic esg expression is required for the maintenance of male germline stem cells.

A family of Snail-related zinc finger proteins regulates two distinct and parallel mechanisms that mediate Drosophila neuroblast asymmetric divisions

Three snail family genes snail, escargot and worniu, encode related zinc finger transcription factors that mediate Drosophila central nervous system (CNS) development. We show that simultaneous removal of all three genes causes defective neuroblast asymmetric divisions; inscuteable transcription/translation is delayed/suppressed in the segmented CNS. Further more, defects in localization of cell fate determinants and orientation of the mitotic spindle in dividing neuroblasts are much stronger than those associated with inscuteable loss of function. In inscuteable neuroblasts, cell fate determinants are mislocalized during prophase and metaphase, yet during anaphase and telophase the great majority of mutant neuroblasts localize these determinants as cortical crescents overlying one of the spindle poles. This phenomenon, known as 'telophase rescue', does not occur in the absence of the snail family genes; moreover, in contrast to inscuteable mutants, mitotic spindle orientation is completely randomized. Our data provide further evidence for the existence of two distinct asymmetry-controlling mechanisms in neuroblasts both of which require snail family gene function: an inscuteable-dependent mechanism that functions throughout mitosis and an inscuteable-independent mechanism that acts during anaphase/telophase.