Basdicmolecularmechanisms for tissue and organ formaiton: HH and FGF-dependent and regulation of positional information and compartment formation

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In the present study, we examined basic molecular mechanisms of development using compound eyes, trachea, legs and visceral mesoderm in Drosophila as model systems. In compound eyes, reiterative use of Spitz signals emanating from already differentiated ommatidial cells triggers the differentiation of around ten different types of cells. We showed evidence that the choice of cell fate by newly recruited ommatidial cells strictly depends on their developmental potential and that developmental potential formation is governed by region-specific prepattern gene expression. Spatial y and temporally regulated activity of Breathless~ranchless signaling is essential for trachea development. We showed that late btl expression is a target of Branchless/Breathless signaling and hence, Branchless/Breathless signaling contains a positive feedback loop, which may guarantee a continuous supply of fresh receptors to membranes of growing tracheal branch cells. We also showed that hi g hI evels of HH si … More gnaling activity are essential for medial-region patterning in legs. In mid-to-late third instar lag discs, high levels of HH signals repress the transcription of pxb, a newly identified gene encoding as transmembrane protein expressed specifically in the anterior compartment. Misexpression experiments indicated that Pxb may serve as a HH signaling attenuator capable of acting prior to HH-Ptc interactions, suggesting tha HH signaling in leg discs includes a pxb-repression-mediated positive feedback loop, run visceral mesoderm gives rise to circular visceral muscles. It has been demonstrated that the trunk visceral mesoderm parasegment is subdivided into at least two domains by connectin expression. We extended this by examining a greater number of visceral mesodermal genes including HH and FGF. Ectodermal HH and Wg differentially regulate the expression of the metameric targets in trunck visceral mesoderm. HH expression in PS3 appeared required for normal Dpp expression and gastric caesum formation. Branchless(FGF) in Vmw as found to serve as a guide for the initial budding of tracheal visceral branches. The metameric pattern of Vm, organized in response to ectodermal instructive signals, is thus maintained at a later time via autoregu I ation, is required for midgut morphogenesis and exerts feedback effect on trachea, ectodermal derivatives. Less