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.

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Planarians have long been studied for their regenerative abilities, but they possess limited genetic tools due to challenges in gene delivery, expression, and detection, despite decades of work. We developed a toolbox for heterologous protein expression in planarian cells and in live animals. Specifically, we identified and optimized nanotechnological and chemical transfection methods to efficiently deliver mRNA encoding nanoluciferase into somatic cells, including planarian adult stem cells (neoblasts). The use of a luminescent reporter allowed us to quantitatively measure protein expression through spectroscopy and microscopy, thus overcoming the strong autofluorescent background of planarian tissues. Using this platform, we investigated the use of endogenous untranslated region (UTR) sequences and codon usage bias to post-transcriptionally alter gene expression. Our work provides a strong foundation for advancing exogenous gene expression and for the rapid prototyping of genetic constructs to accelerate the development of transgenic techniques in planarians.