View Program - 63rd Annual Drosophila Research Conference

Septate junctions (SJs) form an occluding barrier in invertebrate epithelia. More than 30 SJ constituents have been identified and characterized for their canonical barrier function but some studies have highlighted a non-occluding role for SJ genes in Drosophila morphogenesis. In our previous studies, we demonstrated a non-barrier requirement for a subset of core SJ genes during head involution, dorsal closure, and salivary gland development in the fly embryo. However, the mechanistic nature of this requirement is unknown. To address this, we are using dorsal closure (DC) as our model to investigate the morphogenetic function of core SJ genes. DC is a mid-embryogenesis process that seals an epidermal gap, which occurs as a result of germ band retraction. It is driven by actomyosin-based contraction of the extraembryonic amnioserosa cells, tension at the leading-edge, and zippering at the canthi mediated by filopodial dynamics and adhesion. Additionally, cells of the lateral epidermis elongate dorsoventrally and exhibit planar polarized expression of various molecular components including actin, tubulin, and Rab GTPases. Loss-of-function mutations in core SJ genes, including coracle, Macroglobulin complement-related, and Neurexin-IV result in a failure to complete DC and is associated with a dorsal open phenotype in cuticle preparation of embryos. Here we are characterizing cellular defects in SJ mutant embryos that may contribute to their failure in DC. We examined fixed tissue of SJ mutants and observed a lack of a smoothly organized leading-edge during advanced stages of DC. Also, lateral epidermal cells in SJ mutants show significant defects in cell shape, including a lower aspect ratio, reduced area, and increased circularity of their apical surfaces. Additionally, SJ mutants fail to maintain robust organization of microtubules and actomyosin in the epidermis, amnioserosa, and leading-edge towards the end of DC. We are using live confocal imaging to quantify defects in actomyosin dynamics at the leading-edge and amnioserosa in SJ mutants. We are analyzing SJ mutants for subtle alteration in apical-basal polarity of the dorsal epidermal cells that may affect cell shape. We are also examining SJ mutants for defects in localization of Rab GTPases, which may cause reduced polarized trafficking of cytoskeletal and adhesion markers, resulting in defects in cell shape changes and ultimately leading to a defective DC.

Investigating a morphogenetic role for septate junction proteins in cell shape changes and polarity during dorsal closure