A Modifier Screen for Bazooka/PAR-3 Interacting Genes in the Drosophila Embryo Epithelium

Abstract

BackgroundThe development and homeostasis of multicellular organisms depends on sheets of epithelial cells. Bazooka (Baz; PAR-3) localizes to the apical circumference of epithelial cells and is a key hub in the protein interaction network regulating epithelial structure. We sought to identify additional proteins that function with Baz to regulate epithelial structure in the Drosophila embryo.Methodology/Principal FindingsThe baz zygotic mutant cuticle phenotype could be dominantly enhanced by loss of known interaction partners. To identify additional enhancers, we screened molecularly defined chromosome 2 and 3 deficiencies. 37 deficiencies acted as strong dominant enhancers. Using deficiency mapping, bioinformatics, and available single gene mutations, we identified 17 interacting genes encoding known and predicted polarity, cytoskeletal, transmembrane, trafficking and signaling proteins. For each gene, their loss of function enhanced adherens junction defects in zygotic baz mutants during early embryogenesis. To further evaluate involvement in epithelial polarity, we generated GFP fusion proteins for 15 of the genes which had not been found to localize to the apical domain previously. We found that GFP fusion proteins for Drosophila ASAP, Arf79F, CG11210, Septin 5 and Sds22 could be recruited to the apical circumference of epithelial cells. Nine of the other proteins showed various intracellular distributions, and one was not detected.Conclusions/SignificanceOur enhancer screen identified 17 genes that function with Baz to regulate epithelial structure in the Drosophila embryo. Our secondary localization screen indicated that some of the proteins may affect epithelial cell polarity by acting at the apical cell cortex while others may act through intracellular processes. For 13 of the 17 genes, this is the first report of a link to baz or the regulation of epithelial structure.

A contractile actomyosin network linked to adherens junctions by Canoe/afadin helps drive convergent extension

“…In baz mutants, epidermal AJs remain largely intact through the extended germband stage (Shao et al , 2010; Figure 9, G vs. L). Reducing Cno levels promoted earlier disruption of AJs; 21% of extended germband embryos mutant for baz and with reduced Cno had moderate to strong AJ disruption (n = 66; Figure 9, H and I, arrowheads) versus 8% of baz mutants (n = 63).…”

Sds22/PP1 links epithelial integrity and tumor suppression via regulation of myosin II and JNK signaling

“…Although much is known regarding the roles of their kinases such as Par-1 and aPKC, the mechanism of their dephosphorylation is unclear. Recently, sds22 was identified in a geneticinteraction screen with Baz (Shao et al ., 2010), a key regulator of apical membrane polarity and a substrate of PP1 in mouse cell culture (Traweger et al ., 2008), suggesting that sds22/PP1 may act directly on critical components of the cell polarity machinery to maintain epithelial integrity and prevent metastasis. Consistent with this interpretation, we find that overexpression of sds22 can largely suppress the loss-of-function phenotypes of the cell polarity gene scrib .…”

Quantitative proteomics reveals the dynamics of protein changes during Drosophila oocyte maturation and the oocyte-to-embryo transition

“…As a proof of principle, we investigated the role of an evolutionarily conserved, cytoskeletal C-terminal LisH and Kelch-beta-propeller domain-containing protein named Muskelin that is up-regulated during maturation. Muskelin was implicated in regulating adherens junctions in the Drosophila embryo epithelium (33). Interestingly, the founding Kelch domain protein is required for dumping because it is a pivotal constituent of ring canals between the oocyte and its sister nurse cells (34).…”