title: Regulated cationic channel function in Xenopus oocytes expressing Drosophila big brain.
abstract: Big brain (bib) is a neurogenic gene that when mutated causes defects in cell fate determination during Drosophila neurogenesis through an unknown mechanism. The protein Big Brain (BIB) has sequence identity with the major intrinsic protein family that includes the water- and ion-conducting aquaporin channels. We show here that BIB expressed heterologously in Xenopus oocytes provides a voltage-insensitive, nonselective cation channel function with permeability to K+ > Na+ >> tetraethylammonium. The conductance, activated in response to endogenous signaling pathways in BIB-expressing oocytes, is decreased after treatment with 20 microm insulin and is enhanced with 10 microm lavendustin A, a tyrosine kinase inhibitor. Western blot analysis confirms that BIB is tyrosine-phosphorylated. Both tyrosine phosphorylation and the potentiating effect of lavendustin A are removed by partial deletion of the C terminus (amino acids 317-700). Current activation is not observed in control oocytes or in oocytes expressing a nonfunctional mutant (BIB E71N) that appears to be expressed on the plasma membrane by confocal microscopy and Western blotting. These results indicate that BIB can participate in tyrosine kinase-regulated transmembrane signaling and may suggest a role for membrane depolarization in the neurogenic function of BIB in early development.
authors.affiliation: Program in Pharmacology and Toxicology and Department of Pharmacology, College of Medicine, University of Arizona, Tucson, Arizona 85724-5051, USA.
authors.forename: Gina M
authors.initials: GM
authors.lastname: Yanochko
authors.forename: Andrea J
authors.initials: AJ
authors.lastname: Yool
mesh_terms: D000818:Animals; D002412:Cations / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004330:Drosophila; D029721:Drosophila Proteins; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D007328:Insulin / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008845:Microinjections; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D010766:Phosphorylation; D018075:RNA, Complementary / Q000008:administration & dosage; D015398:Signal Transduction / Q000502:physiology; D013329:Structure-Activity Relationship; D014162:Transfection; D014867:Water / Q000378:metabolism; D014981:Xenopus
chemical_list: D002412:Cations; D029721:Drosophila Proteins; D004791:Enzyme Inhibitors; D007328:Insulin; D007473:Ion Channels; D008565:Membrane Proteins; D018075:RNA, Complementary; C070621:bib protein, Drosophila; D014867:Water