Bazooka/PAR3 is dispensable for polarity in Drosophila follicular epithelial cells

Abstract

Apico-basal polarity is the defining characteristic of epithelial cells. In Drosophila, apical membrane identity is established and regulated through interactions between the highly conserved Par complex (Bazooka/Par3, atypical protein kinase C and Par6), and the Crumbs complex (Crumbs, Stardust and PATJ). It has been proposed that Bazooka operates at the top of a genetic hierarchy in the establishment and maintenance of apico-basal polarity. However, there is still ambiguity over the correct sequence of events and cross-talk with other pathways during this process. In this study, we reassess this issue by comparing the phenotypes of the commonly used baz4 and baz815-8 alleles with those of the so far uncharacterized bazXR11 and bazEH747 null alleles in different Drosophila epithelia. While all these baz alleles display identical phenotypes during embryonic epithelial development, we observe strong discrepancies in the severity and penetrance of polarity defects in the follicular epithelium: polarity is mostly normal in bazEH747 and bazXR11 while baz4 and baz815-8 show loss of polarity, severe multilayering and loss of epithelial integrity throughout the clones. Further analysis reveals that the chromosomes carrying the baz4 and baz815-8 alleles may contain additional mutations that enhance the true baz loss-of-function phenotype in the follicular epithelium. This study clearly shows that Baz is dispensable for the regulation of polarity in the follicular epithelium, and that the requirement for key regulators of cell polarity is highly dependent on developmental context and cell type.

Localization and Function of Pals1-associated Tight Junction Protein in Drosophila Is Regulated by Two Distinct Apical Complexes

“…In contrast, in baz-mutant clones, Sdt, PATJ, and Crb are correctly localized to the apical junctions (data not shown and Fig. 2B, mutant clones are marked by the absence of Baz staining), which is in line with recent results showing that baz null alleles do not exhibit polarity defects (32).…”

“…Drosophila Genetics-The following mutant alleles were used: PATJ ⌬1 (21), baz (30,31), baz XR11 (32), sdt K85 (33), and crb 11A22 (34). Germ line clones were generated with the mutant alleles recombined with FRT using the dominant female sterile technique (35).…”

The Clathrin adaptor AP-1 and the Rab-stabilizing chaperone Stratum act in two parallel pathways to control the activation of the Notch pathway in Drosophila

“…Dissection and staining conditions were essentially as previously described (Le Borgne and Schweisguth, 2003). Primary antibodies used were rat anti-Elav (7E10, Developmental Studies Hybridoma Bank (DSHB), 1:200), goat anti-Su(H) (sc15813, Santa Cruz, 1:500), mouse anti-Cut (2B10, DSHB, 1:500), goat anti-Numb (SC23579, Santa Cruz, 1:200), rabbit anti-Spdo (a kind gift from J. Skeath, 1:2000) (O’Connor-Giles and Skeath, 2003), mouse anti-DECD (C594.9B, DSHB, 1:200), mouse anti-Cora (C615.16, DSHB, 1:500), rat anti-DE-Cad (DCAD2, DSHB, 1:500), rabbit anti-Par3 (a kind gift from A. Wodarz, 1:1000) (Shahab et al, 2015), mouse anti-HRS (27-4, DSHB, 1:100), rabbit anti-Syntaxin16 (ab32340, Abcam, 1:1000) and rabbit anti-Dendra (Antibodies-online.com, ABIN361314, 1:1000). Cy2-, Cy3- and Cy5-coupled secondary antibodies (1:400) were from Jackson’s Laboratories.…”

Cdc42 promotes epithelial morphogenesis by coupling Par-complex and Crumbs recruitment via Par6-aPKC

“…Altogether, we hypothesize that this apical fraction of Par6-aPKC is bound to Cdc42 and therefore 380 that both Cdc42 and Baz are able to support apical recruitment of Par6 and aPKC during epithelial morphogenesis. The lack of a requirement for Baz in the follicular epithelium (Shahab et al, 2015) could reflect a more preeminent role for Cdc42 in loading Par6-aPKC at the membrane of these cells when compared to other epithelia.…”