The adaptor protein X11Lalpha/Dmint1 interacts with the PDZ-binding domain of the cell recognition protein Rst in Drosophila.

The Drosophila cell adhesion molecule Rst plays key roles during the development of the embryonic musculature, spacing of ommatidia in the compound eye and of sensory organs on the antenna, as well as in the neuronal wiring of the optic lobe. In rst(CT) mutants lacking the cytoplasmic domain of the Rst protein, cell sorting and apoptosis in the eye are affected, suggesting a requirement of this domain for Rst function. To identify potential interacting proteins, yeast two-hybrid screens were performed using the cytoplasmic domains of Rst and its paralogue Kirre as baits. Among several putative interactors, two paralogous Drosophila PDZ motif proteins related to X11/Mint were identified. X11/Mint family members in C. elegans (LIN-10) and vertebrates are believed to function as adaptor proteins and to regulate the assembly of multi-subunit complexes at the synapse, thereby linking the vesicle cycle to cell adhesion. Using genetic, cell biological, and biochemical approaches, we show that the interaction of Rst with X11Lalpha is of biological significance. The proteins interact, for example, in the context of cell sorting in the pupal retina.

Drosophila Pin1 prolyl isomerase Dodo is a MAP kinase signal responder during oogenesis.

The mammalian cis-trans prolyl isomerase Pin1 and its yeast orthologue Ess1/Ptf1 have been implicated in cell cycle control but a correlation between biochemical and physiological functions has not been established conclusively. Pin1 targets the proline residue carboxy-terminal to the phosphorylated threonine or serine residue, which constitutes part of the phosphorylated mitogen-activated protein kinase (MAPK) site PXpT/SP. Here we show that the Drosophila Pin1 homologue, the Dodo protein, is involved in dorsoventral patterning of the follicular epithelium in the egg chamber. Its function is to facilitate the degradation of transcription factor CF2, which requires, a priori, activated epidermal growth factor receptor-MAPK signalling.

Electrogenic 2 Na/1 H antiport in crustacean epithelium is inhibited by a monoclonal antibody.

We have previously published evidence that suggests that Na/H exchange in crustacean and echinoderm epithelia occurs by an electrogenic antiporter protein with two external cation binding sites that accommodate Na, amiloride, or Ca and display a 2:1 monovalent cation antiport stoichiometry. The present study is an initial investigation into the molecular biology of this invertebrate electrogenic exchanger to ascertain its structural similarity to the analogous vertebrate electroneutral antiport system. A panel of monoclonal antibodies was prepared against components of lobster hepatopancreatic epithelial brush-border membranes and assayed immunohistochemically and by Western blotting. The antibodies were tested further in functional assays for their ability to interfere with electrogenic 2 Na/1 H antiport in isolated hepatopancreatic brush-border membrane vesicles. One cell line was identified producing an antibody that significantly inhibited the electrogenic exchange of cations by these membrane preparations and recognized a single protein band on Western blots of hepatopancreas, antennal gland, and gill epithelia corresponding to a molecular mass of 185 kDa. The existence of such an antibody probe may facilitate the purification of the electrogenic antiporter under denaturing conditions, in in vitro expression systems, or in prokaryotic expression libraries.