A role for Fringe in segment morphogenesis but not segment formation in the grasshopper, Schistocerca gregaria

Studies of somitogenesis in vertebrates have identified a number of genes t hat are regulated by a periodic oscillator that patterns the pre-semitic me soderm. One of these genes, hairy, is homologous to a Drosophila segmentati on gene that also shows periodic spatial expression. This, and the periodic expression of a zebrafish homologue of hairy during somitogenesis, has sug gested that insect segmentation and vertebrate somitogenesis may use simila r molecular mechanisms and possibly share a common origin. In chicks and mi ce expression of the lunatic fringe gene also oscillates in the presomitic mesoderm. Fringe encodes an extracellular protein that regulates Notch sign alling. This, and the finding that mutations in Notch or its ligands disrup t somite patterning, suggests that Notch signalling plays an important role in vertebrate somitogenesis. Although Notch signalling is not known to pla y a role in the formation of segments in Drosophila, we reasoned that it mi ght do so in other insects such as the grasshopper, where segment boundarie s form between cells, not between syncytial nuclei as they do in Drosophila . Here we report the cloning of a single fringe gene from the grasshopper S chistocerca. We show that it is not detectably expressed in the forming tru nk segments of the embryo until after segment boundaries have formed. We co nclude that fringe is not part of the mechanism that makes segments in Schi stocerca. Thereafter it is expressed in a pattern which shows that it is a downstream target of the segmentation machinery and suggests that it may pl ay a role in segment morphogenesis. Like its Drosophila counterpart, Schist ocerca fringe is also expressed in the eye, in rings in the legs, and durin g oogenesis, in follicle cells.