Abstract
Many epithelial tissues undergo extensive remodelling during morphogenesis. How their epithelial features, such as apicobasal polarity or adhesion, are maintained and remodelled and how adhesion and polarity proteins contribute to morphogenesis are two important questions in development. Here, we approach these issues by investigating the role of the apical determinant protein Crumbs (Crb) during the morphogenesis of the embryonic Drosophila tracheal system. Crb accumulates differentially throughout tracheal development and is required for different tracheal events. The earliest requirement for Crb is for tracheal invagination, which is preceded by an enhanced accumulation of Crb in the invagination domain. There, Crb, acting in parallel with the epidermal growth factor receptor (Egfr) pathway, is required for tracheal cell apical constriction and for organising an actomyosin complex, which we propose is mediated by Crb recruitment of moesin (Moe). The ability of a Crb isoform unable to rescue polarity in crb mutants to otherwise rescue their invagination phenotype, and the converse inability of a FERM-binding domain mutant Crb to rescue faulty invagination, support our hypothesis that it is the absence of Crb-dependent Moe enrichment, and not the polarity defect, that mainly underlies the crb invagination phenotype. This hypothesis is supported by the phenotype of lethal giant larvae (lgl); crb double mutants. These results unveil a link between Crb and the organisation of the actin cytoskeleton during morphogenesis.
Highlights
Apicobasal polarity and intercellular adhesion are key features of epithelial tissues and regulate many cellular activities, such as intracellular trafficking, secretion, transepithelial barrier, tissue integrity and homeostasis
Summary Many epithelial tissues undergo extensive remodelling during morphogenesis. How their epithelial features, such as apicobasal polarity or adhesion, are maintained and remodelled and how adhesion and polarity proteins contribute to morphogenesis are two important questions in development
We approach these issues by investigating the role of the apical determinant protein Crumbs (Crb) during the morphogenesis of the embryonic Drosophila tracheal system
Summary
Apicobasal polarity and intercellular adhesion are key features of epithelial tissues and regulate many cellular activities, such as intracellular trafficking, secretion, transepithelial barrier, tissue integrity and homeostasis. The transmembrane protein Crumbs (Crb), a component of the SAR, is considered to be a key apical determinant, as it is able to ‘apicalise’ the membrane upon overexpression, and, in its absence, many tissues lose polarity and adhesion, leading to major epithelial disorganisation (for a review, see Assemat et al, 2008; Gibson and Perrimon, 2003; Tepass et al, 2001). Crb is required to maintain the epithelial polarity during remodelling both of the Malpighian tubules and in the ectoderm undergoing germ band extension (Campbell et al, 2009) Whether it plays an active role in the dynamic processes of morphogenesis has yet to be investigated
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