Re-assessment of the subcellular localization of Bazooka/Par-3 in Drosophila: No evidence for localization to the nucleus and the neuromuscular junction

Bazooka/Par-3 (Baz) is an evolutionarily conserved scaffold protein that together with its binding partners atypical protein kinase C (aPKC) and Par-6 forms the Par complex. This protein complex functions as a master regulator for the establishment and maintenance of cell polarity in many different cell types. In the vast majority of published research papers Par complex members have been reported to localize at the cell cortex and at intercellular junctions. However, there have also been several reports claiming localization and function of Par complex members at additional subcellular sites, in particular the nucleus, the nuclear envelope and the neuromuscular junction. In this study we have re-assessed this issue for Baz in a systematic manner. We used a variety of antibodies raised in different host animals against different epitopes of Baz for confocal imaging of Drosophila tissues. We tested the specificity of these antisera by using mosaic analysis with null mutant baz alleles and tissue-specific RNAi against baz. In addition, we used a GFP-tagged gene trap line for Baz and a bacterial artificial chromosome (BAC) expressing GFP-tagged Baz under control of its endogenous promoter in a baz null mutant background to compare the subcellular localization of the respective GFP-Baz fusion proteins to the staining results with anti-Baz antisera. Together, these experiments did not provide any evidence for specific localization of Baz to the nucleus or the neuromuscular junction.