Genetic control of cell shape changes and rearrangements in Drosophila posterior spiracle development. B. Lovegrove 1, K. Johnson 2, J. Castelli-Gair Hombrìa 1. 1) Department of Zoology, Cambridge University, CAMBRIDGE, UK; 2) Department of Genetics,University of Duesseldorf, 40225 GERMANY.
The organogenesis of the posterior spiracle in abdominal segment 8 has been studied in detail, and has been found to be under the control of the homeotic gene Abd-B. Abd-B mutants have no posterior spiracles, and ectopic spiracles can be induced by Abd-B expression in more anterior segments. Abd-B controls spiracle development by activating a number of downstream target genes, which form a hierarchy. Many of the downstream targets of Abd-B are transcription factors. Some of these activate additional transcription factors downstream, which bring about morphogenetic movements required within particular cells. It is expected that morphogenetic targets such as these will provide the link between the specification by homeotic genes and the intracellular processes of morphogenesis.
The external part of the spiracle is formed by cellular rearrangement. This has been shown to be under the control of the GATA factor GRAIN. It is not known through which target molecules these cell rearrangements occur, or how this process takes place. The interior of the spiracle forms through a process of cell elongation, bringing about the invagination of successive tiers of cells, which acquire a distinctive 'bottle' shape. We have found that the JAK/STAT signalling pathway has a role in controlling this aspect of spiracle morphogenesis. We are investigating what the potential targets of STAT92E might be that could be responsible for these morphogenetic changes within the cells. We will be presenting data indicating that the apical determinant CRUMBS is a potential target of STAT92E in the spiracle, and work on the role of E-cadherin in spiracle development.