AbstractsBiology & Animal Science

Epithelia are key building blocks of many organs. They play important structural and functional roles, such as the establishment of permeability barriers. The insect respiratory system is a vital organ consisting of a tubular network that delivers oxygen to all organs. It develops during embryogenesis and becomes functional just before larval hatching. The system has long been studied as a tractable model to understand the development and function of epithelial tubular organs. A genetic screen had been conducted to identify new candidate genes involved in the development of the fly respiratory system. This screen led to the identification of Btk29A as essential for spiracle morphogenesis and tracheal barrier function. Btk29A encodes for a Tec tyrosine kinase, conserved across vertebrates and invertebrates. The aim of this study was to unravel the role of Btk29A in Drosophila respiratory system. Analysis showed that Btk29A is expressed in the trachea and posterior spiracles. Drosophila posterior spiracles connect the trachea to the environment. They consist of the spiracular chamber and the stigmatophore. Both spiracular compartments express Btk29A. Btk29A mutants display shorter spiracles with abnormal shape. In vivo imaging of posterior spiracles in Btk29A mutants revealed that the invagination is incomplete with the most distal cells failing to invaginate. Parameters known to affect spiracular invagination were examined: apical constriction, cell shape changes, actomyosin organization and activation of Rho1GTPase. None of these parameters seems impaired in Btk29A mutants. Additionally, phenotypic rescue experiments, using the UAS-GAL4 system, showed that recovery of Btk29A by the spiracular chamber cells does not rescue the invagination phenotype, while recovery of the kinase in the stigmatophore leads to normally shaped spiracles. These observations suggest that Btk29A regulates spiracular chamber invagination through regulation of stigmatophore morphogenesis. In vivo imaging showed that Btk29A is indeed important for the regulation of the spatial rearrangements of the stigmatophore cells. The positioning of the spiracular chamber cells and the execution of their invagination is highly dependent on stigmatophore cell rearrangements. Overall, it seems that Btk29A affects spiracle morphogenesis in two ways: it cell-autonomously controls the convergent extension of stigmatophore cells and ensures, non-cell autonomously, the efficient invagination of spiracular chamber cells. The respiratory system of Btk29A mutants is characterised by leaky tracheal permeability barrier. The trachea morphology is not affected. Examination of the Septate Junctions (SJs), which are crucial for the establishment of epithelial permeability barriers in Drosophila, showed that the ultrastructure of the tracheal SJs and the subcellular localization of the SJ proteins, are not impaired in Btk29A mutants. Thus, the permeability phenotype is likely not due to gross impairment in SJ formation or maintenance. This work offers insights into the…