INTEGRATION OF THE HEAD AND TRUNK SEGMENTATION SYSTEMS CONTROLS CEPHALIC FURROW FORMATION IN DROSOPHILA

Genetic and molecular analyses of patterning of the Drosophila embryo have shown that the process of segmentation of the head is fundamental ly different from the process of segmentation of the trunk. The cephal ic furrow (CF), one of the first morphological manifestations of the p atterning process, forms at the juxtaposition of these two patterning systems. We report here that the initial step in CF formation is a cha nge in shape and apical positioning of a single row of cells. The ante roposterior position of these initiator cells may be defined by the ov erlapping expression of the head gap gene buttonhead (btd) and the pri mary pair-rule gene even-skipped (eve). Re-examination of the btd and eve phenotypes in live embryos indicated that both genes are required for CF formation. Further, Eve expression in initiator cells was found to be dependent upon btd activity, The control of eve expression by b td in these cells is the first indication of a new level of integrated regulation that interfaces the head and trunk segmentation systems. I n conjunction with previous data on the btd and eve embryonic phenotyp es, our results suggest that interaction between these two genes both controls initiation of a specific morphogenetic movement that separate s two morphogenetic fields and contributes to patterning the hinge reg ion that demarcates the procephalon from the segmented germ band.