A dual role of the extracellular domain of Drosophila Crumbs for morphogenesis of the embryonic neuroectoderm

摘要

Epithelia are highly polarised tissues and several highly conserved polarity protein complexes serve to establish and maintain polarity. The transmembrane protein Crumbs (Crb), the central component of the Crb protein complex, is required, among others, for the maintenance of polarity in most epithelia in theDrosophilaembryo. However, different epithelia exhibit different phenotypic severity upon loss ofcrb. Using a transgenomic approach allowed us to more accurately define the role ofcrbin different epithelia. In particular, we provide evidence that the loss of epithelial tissue integrity in the ventral epidermis ofcrbmutant embryos is due to impaired actomyosin activity and an excess number of neuroblasts. We demonstrate that the intracellular domain of Crb could only partially rescue this phenotype, while it is able to completely restore tissue integrity in other epithelia. Based on these results we suggest a dual role of the extracellular domain of Crb in the ventral neuroectoderm. First, it is required for apical enrichment of the Crb protein, which in turn regulates actomyosin activity and thereby ensures tissue integrity; and second, the extracellular domain of Crb stabilises the Notch receptor and thereby ensures proper Notch signalling and specification of the correct number of neuroblasts.