The bicistronic gene würmchen encodes two essential components for epithelial development in Drosophila.

Epithelial tissues are fundamental for the establishment and maintenance of different body compartments in multicellular animals. To achieve this specific task epithelial sheets secrete an apical extracellular matrix for tissue strength and protection and they organize a transepithelial barrier function, which is mediated by tight junctions in vertebrates or septate junctions in invertebrates. Here, we show that the bicistronic gene würmchen is functionally expressed in epithelial tissues. CRISPR/Cas9-mediated mutations in both coding sequences reveal two essential polypeptides, Würmchen1 and Würmchen2, which are both necessary for normal epithelial tissue development. Würmchen1 represents a genuine septate junction core component. It is required during embryogenesis for septate junction organization, the establishment of a transepithelial barrier function, distinct cellular transport processes and tracheal system morphogenesis. Würmchen2 is localized in the apical membrane region of epithelial tissues and in a central core of the tracheal lumen during embryogenesis. It is essential during the later larval development.

Conserved function of the matriptase-prostasin proteolytic cascade during epithelial morphogenesis.

Extracellular matrix (ECM) assembly and remodelling is critical during development and organ morphogenesis. Dysregulation of ECM is implicated in many pathogenic conditions, including cancer. The type II transmembrane serine protease matriptase and the serine protease prostasin are key factors in a proteolytic cascade that regulates epithelial ECM differentiation during development in vertebrates. Here, we show by rescue experiments that the Drosophila proteases Notopleural (Np) and Tracheal-prostasin (Tpr) are functional homologues of matriptase and prostasin, respectively. Np mediates morphogenesis and remodelling of apical ECM during tracheal system development and is essential for maintenance of the transepithelial barrier function. Both Np and Tpr degrade the zona pellucida-domain (ZP-domain) protein Dumpy, a component of the transient tracheal apical ECM. Furthermore, we demonstrate that Tpr zymogen and the ZP domain of the ECM protein Piopio are cleaved by Np and matriptase in vitro. Our data indicate that the evolutionarily conserved ZP domain, present in many ECM proteins of vertebrates and invertebrates, is a novel target of the conserved matriptase-prostasin proteolytic cascade.

Expression and function of the zinc finger transcription factor Sp6-9 in the spider Parasteatoda tepidariorum.

Zinc finger transcription factors of the Sp6-9 group are evolutionarily conserved in all metazoans and have important functions in, e.g., limb formation and heart development. The function of Sp6-9-related genes has been studied in a number of vertebrates and invertebrates, but data from chelicerates (spiders and allies) was lacking so far. We have isolated the ortholog of Sp6-9 from the common house spider Parasteatoda tepidariorum and the cellar spider Pholcus phalangioides. We show that the Sp6-9 gene in these spider species is expressed in the developing appendages thus suggesting a conserved role in limb formation. Indeed, RNAi with Sp6-9 in P. tepidariorum leads not only to strong limb defects, but also to the loss of body segments and head defects in more strongly affected animals. Together with a new expression domain in the early embryo, these data suggest that Sp6-9 has a dual role P. tepidariorum. The early role in head and body segment formation is not known from other arthropods, but the role in limb formation is evolutionarily highly conserved.