Analysis of aPKCλ and aPKCζ reveals multiple and redundant functions during vertebrate retinogenesis

Abstract

Retinal lamination is known to depend on cell polarity and localized signaling. In vertebrates, atypical Protein Kinase C proteins, aPKCλ/ι and aPKCζ, are essential for apical-basal cell polarity. However, it is not known to what extent functional redundancy has precluded a comprehensive functional characterization of aPKC signaling during vertebrate retinogenesis. Here, we show that aPKCs λ and ζ are functionally redundant for multiple aspects of retinogenesis including mitotic division location and orientation, cell-type positioning, and retinal pigment epithelial (RPE) and photoreceptor cell morphogenesis. Genetic mosaic analyses demonstrate a cell-autonomous requirement of aPKCs for RPE and photoreceptor development, and a cell-non-autonomous function that is intrinsic to the neural retina for cell-type positioning. Our observations uncover a previously unappreciated involvement of aPKCζ during zebrafish retinogenesis and suggest that aPKC signaling primes the retinal environment for appropriate cell migration of post-mitotic progenitor cells, but is not essential for correct cell-type specification.

Interkinetic Nuclear Migration and the Selection of Neurogenic Cell Divisions during Vertebrate Retinogenesis

“…Wild-type embryos that carried the huc:GFP transgene were injected with morpholinos (MOs; Genetools, Corvallis, OR) specific to aPKC and aPKC mRNA. The translation inhibiting aPKC was used at a concentration of 5 ng/embryo, and the translation inhibiting aPKC MO was used at 8 ng/embryo as described previously (HorneBadovinac et al, 2001;Cui et al, 2007). To determine when huc:GFP expression is initiated, embryos were treated with PTU and monitored under a fluorescence dissecting scope every 15 min beginning at 32 hpf.…”

“…This signaling complex associates with the plasma membrane near tight junction components at the apical end of cells, including retinal neuroepithelia (Izumi et al, 1998;Wodarz, 2002;Suzuki and Ohno, 2006). Disruption of aPKC activity in zebrafish, through genetic mutation in aPKC (heart and soul) or by morpholino knock-down of both aPKC and , leads to a variety of apical-basal cell polarity phenotypes including basallocalized mitoses, altered division plane orientation, and postmitotic cell positioning defects (Horne-Badovinac et al, 2001;Zolessi et al, 2006;Cui et al, 2007). To assess potential affects on neurogenesis, we measured the timing of huc:GFP initiation in both has mutants and aPKC and morphants.…”

Nuclear migration during retinal development

“…These have been shown to have essential roles in cell fate decisions related to cell cycle exit, cell-type choice, and laminar positioning (Malicki, 2004;Gotz and Huttner, 2005). Furthermore, apical junctionassociated signaling molecules such as atypical protein kinase C (aPKC) and Cdc42, via their affects on overall cell polarity, are essential for normal interkinetic nuclear migration (Cappello et al, 2006;Cui et al, 2007). At the basal surface, distinct signaling complexes exist including those associated with focal adhesions (Li and Sakaguchi, 2002;Wozniak et al, 2004).…”

PKCζ regulates Notch receptor routing and activity in a Notch signaling-dependent manner

“…Atypical protein kinase C (aPKC) may be an interesting candidate for control of Notch receptor intracellular trafficking and function, as there is an emerging view that aPKCs play a key role both in regulation of protein trafficking and in various differentiation processes. aPKCs play critical roles in cell polarization [24,25], asymmetric cell division [26,27] and migration [28][29][30], and also link cell polarity cues to differentiation [26,27,[31][32][33][34]. aPKCs are critical regulators of the organization of the apical-basal axis in epithelial cells, a process in which aPKC functions together with PAR-3 and PAR-6 in a complex, and this PAR-3/ PAR-6/aPKC complex is pivotal for establishing cellular polarity and organizing cellular junctions [35][36][37][38].…”