Drosophila Hox and Sex-Determination Genes Control Segment Elimination through EGFR and extramacrochetae Activity

The formation or suppression of particular structures is a major change occurring in development and evolution. one example of such change is the absence of the seventh abdominal segment (a7) in drosophila males. we show here that there is a down-regulation of egfr activity and fewer histoblasts in the male a7 in early pupae. if this activity is elevated,cell number increases and a small segment develops in the adult. at later pupal stages,the remaining precursors of the a7 are extruded under the epithelium. this extrusion requires the up-regulation of the hlh protein extramacrochetae and correlates with high levels of spaghetti-squash,the gene encoding the regulatory light chain of the non-muscle myosin ii. the hox gene abdominal-b controls both the down-regulation of spitz,a ligand of the egfr pathway,and the up-regulation of extramacrochetae,and also regulates the transcription of the sex-determining gene doublesex. the male doublesex protein,in turn,controls extramacrochetae and spaghetti-squash expression. in females,the egfr pathway is also down-regulated in the a7 but extramacrochetae and spaghetti-squash are not up-regulated and extrusion of precursor cells is almost absent. our results show the complex orchestration of cellular and genetic events that lead to this important sexually dimorphic character change. © 2012 foronda et al.