Espinas, M. L. | Search bioRxiv

bioRxiv2023

Wengen, a Tumour Necrosis Factor Receptor, regulates the Fibroblast Growth Factor pathway by an unconventional mechanism

Unveiling the molecular mechanisms of receptor activation has led to much understanding of development as well as the identification of important drug targets. We use the Drosophila tracheal system to study the activity of two families of widely used and conserved receptors, the TNFRs and the RTK-FGFRs. Breathless, an FGFR, is known to respond to ligand by activating the differentiation program of the tracheal terminal cell. Here we show that Wengen, a TNFR, acts independently of both its canonical ligand and its downstream pathway genes to repress terminal cell differentiation. In contrast to Breathless, Wengen does not stably localise at the membrane and is instead internalised -- a trafficking that seems essential for activity. We find that Wengen forms a complex with Breathless, and both colocalise in intracellular vesicles. Furthermore, Wengen regulates Breathless accumulation, likely regulating Breathless intracellular trafficking and degradation. We propose that, in the tracheal context, Wengen interacts with Breathless to regulate its activity in terminal cell differentiation. We suggest that such unconventional mechanism, involving binding by TNFRs to unrelated proteins, may be a general strategy of TNFRs activity.

developmental biology↗

bioRxiv2022

Dissecting the roles of Expansion/Rebuf and the chitin synthase Krotzkopf Verkehrt in chitin deposition in Drosophila

Chitin is a highly abundant polymer in nature and a principal component of apical extracellular matrices in insects. In addition, chitin has proved to be an excellent biomaterial with multiple applications. In spite of its importance, the molecular mechanisms of chitin biosynthesis and chitin structural diversity are not fully elucidated yet. To investigate these issues, we use Drosophila as a model. We previously showed that chitin deposition in ectodermal tissues requires the concomitant activities of the chitin synthase enzyme Kkv and the functionally interchangeable proteins Exp and Reb. Here we carry out a cellular and molecular analysis of chitin deposition and we show that chitin polymerisation and chitin translocation to the extracellular space are uncoupled. We find that Kkv activity in chitin translocation, but not in polymerisation, requires the activity of Exp/Reb, and in particular of its conserved N-MH2 domain. The activity of Kkv in chitin polymerisation and translocation correlate with Kkv subcellular localisation, and in absence of Kkv-mediated extracellular chitin deposition, chitin accumulates intracellularly as membrane-less punctae. Furthermore, we find that Kkv and Exp/Reb display a largely complementary pattern at the apical domain, and that Exp/Reb activity regulates the topological distribution of Kkv at the apical membrane. We propose a model in which Exp/Reb regulates the organisation of Kkv complexes at the apical membrane which, in turn, regulates the function of Kkv in extracellular chitin translocation.

developmental biology↗