RESUMEN
Embryos deficient for an essential gene may show complex phenotypes that reflect pleiotropic functions and non-cell-autonomous requirements for the encoded protein. The generation of mosaic animals, where most cells are wild type, but a few cells are mutant, is a powerful tool permitting the detailed analysis of the cell autonomous function of a gene, in a particular cell type, at cellular and subcellular resolutions. Here we apply this method to the analysis of the Cerebral Cavernous Malformations 3 (CCM3) pathway in Drosophila.The conserved CCM3 protein functions together with its binding partner, Germinal Center Kinase III (Wheezy/GckIII in Drosophila, MST3, STK24, and STK25 in human) in the regulation of tube morphogenesis (Bergametti et al. Am J Hum Genet. 76:42-51, 2005; Fidalgo et al. J Cell Sci. 123:1274-1284, 2010; Guclu et al. Neurosurgery. 57:1008-1013, 2005; Lant et al. Nat Commun. 6:6449, 2015; Song et al. Dev Cell. 25:507-519, 2013; Ceccarelli et al. J Biol Chem. 286:25056-25064, 2011; Rehain-Bell et al. Curr Biol. 27:860-867, 2017; Xu et al. Structure. 21:1059-1066, 2013; Zhang et al. Front Biosci. 17:2295-2305, 2012; Zhang et al. Dev Cell. 27:215-226, 2013; Zheng et al. J Clin Invest. 120:2795-2804, 2010). The Drosophila proteins play a role in the regulation of tube shape in the tracheal (respiratory) system, analogous to the role of the human proteins in the vascular system. To understand the cellular basis for tube dilation defects caused by loss of pathway function, we describe techniques for the generation and analysis of positively marked homozygous mutant GckIII tracheal cells, coupled with an "open book" preparation that can be subjected to immunofluorescent analysis. Dozens of mutant tracheal cells are generated per mosaic animal, and neighboring heterozygous cells in the same animal serve as ideal internal controls.