Abstract
ABSTRACTEpithelia 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 the Drosophila embryo. However, different epithelia exhibit different phenotypic severity upon loss of crb. Using a transgenomic approach allowed us to more accurately define the role of crb in different epithelia. In particular, we provide evidence that the loss of epithelial tissue integrity in the ventral epidermis of crb mutant 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.
Highlights
Epithelia are highly polarised tissues that can be specialised for protection, absorption, secretion, transport or sensory perceptions
We show that fosmid-based expression of the intracellular domain (ICD) rescues polarity defects in most epithelia of crb mutant embryos, and, and in contrast to results obtained from overexpression studies, is sufficient for proper invagination and morphogenesis of epithelial tubes and, strikingly, for viability in about 50% of cases
In order to dissect the functions of the intracellular and extracellular domain of Crb in embryonic development under physiological conditions, we modified foscrb and foscrbEGFP to generate two transgenes. foscrbICD encodes a membrane bound ICD of Crb, in which the ECD was deleted with the exception of the C-terminal 8 amino acids (KEAYFNGS). foscrbECD-EGFP encodes an Enhanced Green Fluorescent Protein (EGFP)-tagged membrane-bound ECD, in which most of the ICD has been deleted with the exception of the N-terminal 7 amino acids (MARNKRAT) (Fig. 1A). foscrbICD, foscrbECD-EGFP as well as a fosmid encoding EGFP-tagged fulllength Crb proteins were integrated into the VK00033 landing site
Summary
Epithelia are highly polarised tissues that can be specialised for protection, absorption, secretion, transport or sensory perceptions. Mechanisms controlling polarity and integrity of epithelial tissues are important for shaping tissues during development. Maintaining polarity is essential for tissue homeostasis in adult organisms, which is reflected by the fact that 80-90% of all cancer types derive from epithelia (Cao et al, 2015; Grifoni et al, 2013; Laprise, 2011; McCaffrey and Macara, 2011; Tellkamp et al, 2014). Unravelling the basis of epithelial polarity and the mechanisms required to maintain tissue integrity is crucial to understand the origin of various diseases. Drosophila embryonic epithelia are excellent model tissues to study the genetic, molecular and cellular basis of development and maintenance of polarity. Studies focussing on the embryonic epidermis have provided deep insight into the regulation of tissue polarity and
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
