Abstract
BackgroundCell polarity genes including Crumbs (Crb) and Par complexes are essential for controlling photoreceptor morphogenesis. Among the Crb and Par complexes, Bazooka (Baz, Par-3 homolog) acts as a nodal component for other cell polarity proteins. Therefore, finding other genes interacting with Baz will help us to understand the cell polarity genes' role in photoreceptor morphogenesis.Methodology/Principal FindingsHere, we have found a genetic interaction between baz and centrosomin (cnn). Cnn is a core protein for centrosome which is a major microtubule-organizing center. We analyzed the effect of the cnn mutation on developing eyes to determine its role in photoreceptor morphogenesis. We found that Cnn is dispensable for retinal differentiation in eye imaginal discs during the larval stage. However, photoreceptors deficient in Cnn display dramatic morphogenesis defects including the mislocalization of Crumbs (Crb) and Bazooka (Baz) during mid-stage pupal eye development, suggesting that Cnn is specifically required for photoreceptor morphogenesis during pupal eye development. This role of Cnn in apical domain modulation was further supported by Cnn's gain-of-function phenotype. Cnn overexpression in photoreceptors caused the expansion of the apical Crb membrane domain, Baz and adherens junctions (AJs).Conclusions/SignificanceThese results strongly suggest that the interaction of Baz and Cnn is essential for apical domain and AJ modulation during photoreceptor morphogenesis, but not for the initial photoreceptor differentiation in the Drosophila photoreceptor.
Highlights
Genetic control of apical-basal cell polarity is essential for epithelial morphogenesis and asymmetric cell division during cell fate specification [1]
Conclusions/Significance: These results strongly suggest that the interaction of Baz and Cnn is essential for apical domain and adherens junctions (AJs) modulation during photoreceptor morphogenesis, but not for the initial photoreceptor differentiation in the Drosophila photoreceptor
In the cnn/+ heterozygous background to reduce the Cnn level, the rough-eye phenotype of GMR.Baz was strongly enhanced. This genetic interaction data strongly suggests that Cnn may provide an additional positional and/or maintenance cue for Crb and AJ positioning, because the Crb/AJ mislocalization caused by Baz overexpression further enhanced by the reduced cnn gene dosage (Figure 2)
Summary
Genetic control of apical-basal cell polarity is essential for epithelial morphogenesis and asymmetric cell division during cell fate specification [1] It is important for development of polarized subcellular structures with specialized functions such as the light sensing organelles of photoreceptor cells [2,3]. A small number of evolutionarily conserved proteins play important roles in diverse types of apical-basal cell polarization These polarity proteins form two major heterotrimeric cassettes consisting of CrbStardust (Sdt)-Patj (Crb complex) and Par-6-aPKC-Baz (Par complex) in the apical cell membrane [1]. Crb complex proteins are localized immediately apical to AJs (Figure 1) During this time, developing photoreceptors undergo dramatic vertical extension from the distal region of photoreceptor cells to the proximal base of the retina. Finding other genes interacting with Baz will help us to understand the cell polarity genes’ role in photoreceptor morphogenesis
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