Role of Kinesin Heavy Chain in Crumbs Localization along the Rhabdomere Elongation in Drosophila Photoreceptor

Abstract

BackgroundCrumbs (Crb), a cell polarity gene, has been shown to provide a positional cue for the extension of the apical membrane domain, adherens junction (AJ), and rhabdomere along the growing proximal-distal axis during Drosophila photoreceptor morphogenesis. In developing Drosophila photoreceptors, a stabilized microtubule structure was discovered and its presence was linked to polarity protein localization. It was therefore hypothesized that the microtubules may provide trafficking routes for the polarity proteins during photoreceptor morphogenesis. This study has examined whether Kinesin heavy chain (Khc), a subunit of the microtubule-based motor Kinesin-1, is essential in polarity protein localization in developing photoreceptors.Methodology/Principal FindingsBecause a genetic interaction was found between crb and khc, Crb localization was examined in the developing photoreceptors of khc mutants. khc was dispensable during early eye differentiation and development. However, khc mutant photoreceptors showed a range of abnormalities in the apical membrane domain depending on the position along the proximal-distal axis in pupal photoreceptors. The khc mutant showed a progressive mislocalization in the apical domain along the distal-proximal axis during rhabdomere elongation. The khc mutation also led to a similar progressive defect in the stabilized microtubule structures, strongly suggesting that Khc is essential for microtubule structure and Crb localization during distal to proximal rhabdomere elongation in pupal morphogenesis. This role of Khc in apical domain control was further supported by khc's gain-of-function phenotype. Khc overexpression in photoreceptors caused disruption of the apical membrane domain and the stabilized microtubules in the developing photoreceptors.Conclusions/SignificanceIn summary, we examined the role of khc in the regulation of the apical Crb domain in developing photoreceptors. Since the rhabdomeres in developing pupal eyes grow along the distal-proximal axis, these phenotypes suggest that Khc is essential for the microtubule structures and apical membrane domains during the distal-proximal elongation of photoreceptors, but is dispensable for early eye development.

Development and dynamics of cell polarity at a glance

“…Kinesins, which are plus-end-directed microtubule motors, might also aid in apical transport of polarity proteins, which would require a subset of microtubules to orient their plus-ends apically. Kinesins drive the apical delivery of Crb in adult eyes, but it is not yet known whether this is also true in other epithelia (League and Nam, 2011). In addition to the positive regulators of Crb localization, basolaterally localized yurt and coracle prevent basolateral diffusion of Crb, thus stabilizing basolateral identity (Laprise et al, 2006(Laprise et al, , 2009.…”

Integration of a faculty's ongoing research into an undergraduate laboratory teaching class in developmental biology

“…Immunohistochemistry: Fluorescent immunostaining of imaginal discs and pupal eyes were carried out as reported [9][10][11][12][13][14][15]. The following primary antibodies were used: mouse anti-a-Spectrin (Developmental Studies Hybridoma Bank), 1:25; rat anti-Elav (Developmental Studies Hybridoma Bank), 1:25.…”

“…The pupal eye development was utilized for the instructor's main research material for the last 16 years. The instructor has analyzed cell polarity, cell junctions, and cytoskeletons using this important organogenesis model system [9,10,[12][13][14][15][22][23][24][25][26][27].…”

Role of Tau, a microtubule associated protein, in Drosophila photoreceptor morphogenesis

“…The microtubule regulators and microtubule-dependent motors were found to be involved in photoreceptor cell polarity in pupal photoreceptors (Chen et al, 2010(Chen et al, , 2011League and Nam, 2011;Mui et al, 2011;Mukhopadhyay et al, 2010;Nam, 2013Nam, , 2015. Therefore, the Tau might have a role in a microtubule-based trafficking and/or trafficking of cell polarity proteins as a microtubule stabilizer (Doerflinger et al, 2003;Weingarten et al, 1975;Witman et al, 1976) in photoreceptor cell polarity.…”

“…But, there are several cases which report that some genes have no roles in early eye differentiation but have important roles in late-stage eye morphogenesis. For example, our previous studies showed that crb, par-1, and kinesin-I have no roles in photoreceptor cell polarity formation and/or maintenance in eye imaginal discs during third-instar larval stage (Bayraktar et al, 2006;Izaddoost et al, 2002;League and Nam, 2011;Pellikka et al, 2002), but they actually have important roles in photoreceptor morphogenesis during pupal stage (Izaddoost et al, 2002;League and Nam, 2011;Nam et al, 2007;Pellikka et al, 2002). Therefore, the potential role of Tau in microtubule structures and photoreceptor cell polarity needs to be examined in developing pupal eyes where the photoreceptor cells undergo dramatic reorganization and exponential distal-proximal extension (Kumar and Ready, 1995;Longley and Ready, 1995).…”