Discs-Large and Strabismus are functionally linked to plasma membrane formation

During early embryogenesis in Drosophila melanogaster, extensive vesicle transport occurs to build cell boundaries for 6,000 nuclei. Here we show that this important process depends on a functional complex formed between the tumour suppressor and adaptor protein Discs-Large (Dlg) and the integral membrane protein Strabismus (Stbm)/Van Gogh (Vang). In support of this idea, embryos with mutations in either dlg or stbm displayed severe defects in plasma membrane formation. Conversely, overexpression of Dlg and Stbm synergistically induced excessive plasma membrane formation. In addition, ectopic co-expression of Stbm (which associated with post-Golgi vesicles) and the mammalian Dlg homologue SAP97/hDlg promoted translocation of SAP97 from the cytoplasm to both post-Golgi vesicles and the plasma membrane. This effect was dependent on the interaction between Stbm and SAP97. These findings suggest that the Dlg-Stbm complex recruits membrane-associated proteins and lipids from internal membranes to sites of new plasma membrane formation.