1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

445 Poster Developmental, Neurogenesis, and ConsumerResearchDEVELOPMENTAL EFFECTS OF LINGUAL NERVETRANSECTION ON TASTE BUD VOLUMES IN RATGomez A.M. 1 , Sollars S.I. 1 1 Psychology, University of Nebraska atOmaha, Omaha, NEThe present study examined the role of the lingual nerve in themaintenance of taste buds located in fungiform papillae at variousdevelopmental ages. Rats underwent unilateral lingual nerve transectionon postnatal days 10, 25, or 65. Care was taken to avoid injury to thechorda tympani nerve. Following 2, 8, 16, or 50 days survival time,analysis of taste bud volume was conducted. Results identified adevelopmental effect of this procedure; transection of the lingual nerveon P10 resulted in a complete absence of taste buds following 8 and 16days survival time. Transection on P25 resulted in a significantreduction in taste bud volume relative to control sides of the tonguefollowing 8 days survival time (p < 0.05), but no apparent reduction inthe number of taste buds on the control versus intact tongue sides.Transection on P65 did not significantly alter taste bud volumes or thenumber of taste buds identified, regardless of survival time.Furthermore, morphological analyses identified the presence offiliform-like structures as early as 2 days posttransection in all groups(i.e., P10, P25, P65), and the persistance of these structures following50 days survival time in P10 and P25 transected rats. These findingsfurther demonstrate earlier results from our laboratory showing theimportance of sensory innervation during early gustatory developmentin rats and for the first time identify the lingual nerve as an integralcomponent in the early maintenance of taste buds in fungiform papillae.446 Poster Developmental, Neurogenesis, and ConsumerResearchWITHDRAWN447 Poster Developmental, Neurogenesis, and ConsumerResearchWNT/-CATENIN SIGNALING MODULATES DEVELOPMENTOF TASTE PRIMORDIAThirumangalathu S. 1 , Stoick-Cooper C.L. 2 , Moon R.T. 3 , Barlow L.A. 11 Cell & Developmental Biology, University of Colorado HealthSciences Center, Aurora, CO; 2 Neurobiology & Behavior GradProgram, University of Washington, Seattle, WA;3 HHMI/Pharmacology, University of Washington, Seattle, WAWnt genes are key regulators of embryonic development. Thesesecreted factors bind Frizzled receptors to activate the ß-cateninpathway. To determine if Wnt signaling is involved in the developmentof taste papillae, we examined Wnt reporter gene activity in tongues ofembryonic TOPGAL mice (DasGupta & Fuchs, 1999). Wnt signalingis first evident in anterior lingual epithelium on embryonic day (E)12.0,then focuses to papillary placodes as these taste primordia form (E12.5).Wnt activity persists in taste papillae, and at lower levels in lingualepithelium, as morphogenesis ensues. We have identified Wnt6 andWnt10a via RT-PCR of lingual mRNA as likely activators of TOPGALin embryonic tongues. Frizzled receptors 2-5, 7 and 8, secretedantagonists Dkk 1-3, and coreceptor LRP5/6 are also expressed indeveloping tongue coincident with Wnt6 and 10a. In sum, our datasuggest that Wnts function in taste papilla formation, morphogenesisand/or differentiation. To test this hypothesis, embryonic tonguecultures were exposed at E11.5 to lithium (Li + ), which activates Wntsignaling by stabilizing cytoplasmic ß-catenin. Explants treated with Li +had significantly more papillae than controls, implying that early Wntsignaling promotes taste primordia development. We are now exploringthe expression patterns of Wnt6 and 10a with respect to embryonicpapillae, and testing the specificity of Wnt action in vitro. Supported byNIDCD DC03947 to LAB448 Poster Poster #7 - Developmental, Neurogenesis, andConsumer ResearchCELL SIGNALING IN EGF REGULATION OF FUNGIFORMPAPILLA PATTERNINGLiu H.X. 1 , Henson B.S. 1 , Zhou Y.Q. 1 , D'Silva N.J. 1 , Mistretta C.M. 11 School of Dentistry, University of Michigan, Ann Arbor, MIWe demonstrated previously that exogenous epidermal growth factor(EGF) regulates patterning of fungiform papillae by reducing papillanumber and increasing cell proliferation between papillae in embryonicrat tongue cultures. Using specific inhibitors, we also found thatsignaling through protein kinases, PI3K/Akt, MEK/ERK and p38MAPK, mediates these responses to EGF. In the present study weinvestigate whether EGF-mediated effects on tongue papillae areinduced via the EGF receptor (EGFR) and further explore intracellularsignaling events. Compound 56, a specific inhibitor of EGFR, inducedan increase in papilla number, completely blocking the EGF effect inembryonic day 14 tongue cultures. Using immunolocalization andimmunoblot endpoint assays, EGF-mediated phosphorylation of Akt,ERK, and p38 MAPK in tongue cultures was observed. In the absenceof EGF, inhibition of PI3K/Akt, MEK/ERK, and p38 MAPK withLY294002, U0126 or SB203580 respectively, showed no significantchange in papilla number. However, MEK/ERK inhibition, inconjunction with inhibition of PI3K/Akt or p38 MAPK or both,increased papilla number, blocking any EGF-mediated action,consistent with a synergistic effect. In contrast, concurrent inhibition ofPI3K/Akt and p38 MAPK had no effect. These results demonstrate thatthe EGF effect on fungiform papillae is mediated by EGFR, viaPI3K/Akt, MEK/ERK, and p38 MAPK signaling and suggest asynergistic role of MEK/ERK pathway with PI3K/Akt or p38 MAPK inEGF-mediated papilla patterning. Supported by NIH Grants NIDCDDC00456 (CMM), NIDCR DE00452 (NJD).112