title: Expression of genes encoding multi-transmembrane proteins in specific primate taste cell populations.
abstract: BACKGROUND
  Using fungiform (FG) and circumvallate (CV) taste buds isolated by laser capture microdissection and analyzed using gene arrays, we previously constructed a comprehensive database of gene expression in primates, which revealed over 2,300 taste bud-associated genes. Bioinformatics analyses identified hundreds of genes predicted to encode multi-transmembrane domain proteins with no previous association with taste function. A first step in elucidating the roles these gene products play in gustation is to identify the specific taste cell types in which they are expressed.
  
  
  RESULTS
  Using double label in situ hybridization analyses, we identified seven new genes expressed in specific taste cell types, including sweet, bitter, and umami cells (TRPM5-positive), sour cells (PKD2L1-positive), as well as other taste cell populations. Transmembrane protein 44 (TMEM44), a protein with seven predicted transmembrane domains with no homology to GPCRs, is expressed in a TRPM5-negative and PKD2L1-negative population that is enriched in the bottom portion of taste buds and may represent developmentally immature taste cells. Calcium homeostasis modulator 1 (CALHM1), a component of a novel calcium channel, along with family members CALHM2 and CALHM3; multiple C2 domains; transmembrane 1 (MCTP1), a calcium-binding transmembrane protein; and anoctamin 7 (ANO7), a member of the recently identified calcium-gated chloride channel family, are all expressed in TRPM5 cells. These proteins may modulate and effect calcium signalling stemming from sweet, bitter, and umami receptor activation. Synaptic vesicle glycoprotein 2B (SV2B), a regulator of synaptic vesicle exocytosis, is expressed in PKD2L1 cells, suggesting that this taste cell population transmits tastant information to gustatory afferent nerve fibers via exocytic neurotransmitter release.
  
  
  CONCLUSIONS
  Identification of genes encoding multi-transmembrane domain proteins expressed in primate taste buds provides new insights into the processes of taste cell development, signal transduction, and information coding. Discrete taste cell populations exhibit highly specific gene expression patterns, supporting a model whereby each mature taste receptor cell is responsible for sensing, transmitting, and coding a specific taste quality.
authors.affiliation: Senomyx, Inc, San Diego, California, United States of America. bryan.moyer@senomyx.com
authors.forename: Bryan D
authors.initials: BD
authors.lastname: Moyer
authors.forename: Peter
authors.initials: P
authors.lastname: Hevezi
authors.forename: Na
authors.initials: N
authors.lastname: Gao
authors.forename: Min
authors.initials: M
authors.lastname: Lu
authors.forename: Dalia
authors.initials: D
authors.lastname: Kalabat
authors.forename: Hortensia
authors.initials: H
authors.lastname: Soto
authors.forename: Fernando
authors.initials: F
authors.lastname: Echeverri
authors.forename: Bianca
authors.initials: B
authors.lastname: Laita
authors.forename: Shaoyang Anthony
authors.initials: SA
authors.lastname: Yeh
authors.forename: Mark
authors.initials: M
authors.lastname: Zoller
authors.forename: Albert
authors.initials: A
authors.lastname: Zlotnik
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000235:genetics; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D009928:Organ Specificity / Q000235:genetics; D011323:Primates / Q000235:genetics*; D021381:Protein Transport; D050053:TRPM Cation Channels / Q000235:genetics / Q000378:metabolism; D050396:TRPP Cation Channels / Q000235:genetics / Q000378:metabolism; D013650:Taste Buds / Q000166:cytology* / Q000378:metabolism*
chemical_list: D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D050053:TRPM Cation Channels; D050396:TRPP Cation Channels