The Role of Zasp52 in the Morphogenesis of the Drosophila melanogaster Embryo
Actomyosin cables are supracellular structures present during the development of many metazoans. After their initial description during wound healing in chick embryos, they have now been observed in diverse morphogenetic processes. It is currently unknown whether all supracellular actomyosin structures across species and developmental processes share unique features, such as protein composition or organisation of components of morphogenetic functions. In order to study common features and possibly functions of supracellular actomyosin cables in the fruit fly embryo, this work capitalised on prior findings that the protein Zasp52 is enriched at the site of the supracellular actomyosin structure during dorsal closure. I now show that Zasp52 possesses a potential actin binding motif related to the one found in capping protein/CapZ across metazoans, and this motif is sufficient to bind actin in vitro. Zasp52’s in vivo localisation to actomyosin cables together with an observed reduction of Factin when Zasp52 is depleted suggest that Zasp52 is both a marker and a key component of supracellular actomyosin cables. Zasp52 is localised to a number of supracellular actomyosin cables in the fly embryo, but not all of them: The tissues where Zasp52 localises to supracellular actomyosin structures have in common that they undergo large-scale morphogenetic changes, while those that lack Zasp52 expression are structures found in tissues where the morphogenetic impact is smaller, i.e. fewer cells change their physical location over time. This suggests that Zasp52 is aiding in the morphogenesis of such events leading to large topology changes and that are accompanied by stronger physical forces present in the tissue. Mass spectrometric analysis of co-immunoprecipitations using endogenously-tagged Zasp52 as a bait revealed that Zasp52 is interacting with a number proteins and protein complexes at the apical, sub-apical and lateral junctions as well as with actin-modulating proteins, especially proteins that cap F-actin. Ectopic overexpression of Zasp52 is sufficient to localise it to junctions, illustrating that this localisation does not depend on a specific morphogenetic process. Complete loss of Zasp52 leads to the disorganisation of the embryo architecture with severe deformations of various ectoderm-derived tissues observed in the majority of embryos. Thus, I propose that Zasp52 is an integral component of a subset of supracellular actomyosin structures during embryonic development. These supracellular actomyosin structures are involved in the coordination of morphogenetic processes across the epidermis during embryogenesis as part of a network that contributes to morphogenesis.