1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

297 Slide Peripheral OlfactionROLES OF TRPM5 IN MOUSE OLFACTORY SIGNALTRANSDUCTIONLin W. 1 , Margolskee R.F. 2 , Restrepo D. 1 1 Cell and Devel. Biol,Neuroscience Program and Rocky Mountain Taste and Smell Center,University of Colorado at Denver and Health Sciences Center, Aurora,CO; 2 Neuroscience, Mount Sinai School of Medicine, New York, NYPreviously, we have reported responsiveness to putative pheromonesin mice defective for the cyclic nucleotide-gated channel (CNGA2) (Linet al., J. Neurosci. 24: 3703, 2004) and expression of TRPM5, atransient receptor potential channel, in olfactory sensory neurons(OSNs) (Lin et al., AChemS abstract, 2005). In the present study, wecharacterized the role of TRPM5 in signal transduction byimmunolabeling and electro-olfactogram (EOG) recordings in knockout(KO) mice. In contrast to normal mice, where inhibitors of the cAMPsignaling pathway suppressed putative pheromone-evoked EOGresponses differentially from responses to other odorants, responses toboth types of odorants were similarly inhibited in TRPM5 KO mice.Using Fos protein expression as a measure of odor-elicited activity, wefind that putative pheromones and urine activated some but not allglomeruli receiving input from TRPM5-expressing OSNs. OdorevokedFos expression in bulbs was reduced significantly in double KOmice lacking both CNGA2 and TRPM5. Unexpectedly, profoundabnormalities were observed in the double KOs as compared to CNGA2or TRPM5 single KOs, which include smaller bulb and glomerular size,depletion of mature OSNs and disappearance of glomeruli in discreteregions of the bulb. These data suggest TRPM5 is important forolfactory signal transduction and for activity-dependent survival ofolfactory neurons and maintenance of the glomeruli. Supported by NIHgrants DC00566, DC04657, DC006070 (DR), DC006828 (WL), andDC03155 (RFM).299 Slide Peripheral OlfactionTHE WNT2 AND WNT5 GENES REGULATE DIFFERENTSTEPS IN OLFACTORY MAP DEVELOPMENTYin C. 1 , Ying Y. 1 , Ozawa R. 1 , Wu Y. 1 , Liebl F. 1 , Fradkin L. 2 , Aigaki T. 3 ,Hing H.K. 1 1 Cell and Developmental Biology, University of Illinois atUrbana-Champaign, Urbana, IL; 2 Medical Center, Leiden University,Leiden, Netherlands; 3 Biological Sciences, Tokyo MetropolitanUniversity, Tokyo, JapanThe molecular mechanisms regulating the precise arrangement ofglomeruli in the olfactory map are poorly understood. Our long-termgoals are to identify the molecules and elucidate their functions. Werecently found that two members of the Wnt family of secreted proteinsare necessary for the precise anatomy of the Drosophila antennal lobes(ALs). Mutation in wnt5 severely disrupts the arrangement of glomeruliin the fly ALs. The derailed (drl) transmembrane receptor tyrosinekinase has been proposed to act as Wnt5 receptor. Mutation in drl alsoseverely alters glomerular pattern. Loss of drl functions leads toenhancement of wnt5 activity, indicating that wnt5 and drl functionstogether in patterning the fly olfactory map. In the double mutant, wnt5is epistatic over drl, indicating that wnt5 functions downstream of drl.Cell-type specific genetic rescue showed that wnt5 acts in the olfactorysensory neurons while drl acts in glial cells. We propose that olfactoryneurons express wnt5 which patterns the olfactory map by regulatingthe development of glial cells. We recently also observed that wnt2 isnecessary for AL development. Unlike the glomeruli of the wnt5mutant, which are relatively normal, those of wnt2 are indistinct andmisshapen, indicating that wnt2 functions in glomerular establishmentrather than patterning. Our preliminary analyses indicate that thedendritic trees of the projection neurons in the wnt2 mutant fail tocoalesce into distinct glomerular structures. In summary, we found thattwo secreted proteins, Wnt2 and Wnt5, functions at different steps todirect the formation and patterning of glomeruli in the fly ALs.298 Slide Peripheral OlfactionTHE ROLE OF THE TRANSCRIPTION FACTOR OAZ IN ORNDEVELOPMENTCheng L. 1 , Reed R.R. 1 1 Molecular Biology and Genetics, JohnsHopkins University, Baltimore, MDThe generation of mature olfactory receptor neurons (ORNs) requirescomplex regulation by several classes of transcription factors. Previousstudies have implicated the O/E family of transcription factors in theregulation of genes essential for olfactory function (ACIII, Golf,CNGCs, and ORs). The multiple zinc finger transcription factor OAZ(O/E1 associated zinc finger protein) interacts with all of the O/E familymembers and is preferentially expressed in immature neurons where itis proposed to block O/E function. We have used genetic mouse modelsto explore the role of OAZ in ORN development. In OAZ-null mice, theprojection of ORN axons to the dorsal olfactory bulb was severelyimpaired. Examination of individual glomeruli showed poorconvergence and a ventral shift. To test the hypothesis that OAZfunctions as an O/E inhibitor in early ORN differentiation, we created"gain-of-function" mutant mice by overexpressing OAZ using the O/E3promoter. When expression of OAZ was maintained in thedifferentiating cells, ORN maturation was arrested at a differentiationstage consistent with the first expression of ORs, and nearly allprojections to the olfactory bulb were abolished. This studydemonstrates that OAZ functions as a molecular switch in ORNdevelopment, mediating the transition from differentiation to maturationphenotype.300 Slide Central OlfactionGLOMERULAR COMPUTATIONS IN THE OLFACTORYBULB CAN NORMALIZE NEURAL ACTIVATION PATTERNSCleland T. 1 , Johnson B. 2 , Leon M. 2 , Linster C. 1 1 Dept Neurobiol &Behav, Cornell Univ, Ithaca, NY; 2 Dept Neurobiol & Behav, Universityof California, Irvine, Irvine, CAIncreasing the concentration of most odorants elevates responseintensity and activates increasing numbers of glomeruli in the olfactorybulb. Given this, one might predict (1) that the identity of the perceivedodor would be altered due to the newly activated glomeruli and (2) thatit would be more difficult to discriminate between closely relatedodorants due to the greater overlap between their responses. In fact,most odorants do not change in quality with increasing concentration,and higher concentration odors are easier, not harder, to discriminate.Notably, when glomerular activation data are normalized with respect tothe overall level of activity, odor-specific glomerular activity patternsremain relatively invariant with increasing concentration. Furthermore,the presence of feedforward inhibitory circuits within glomeruli,coupled with the fact that mitral cell responses to increasing odorconcentrations do not reflect the monotonic increases in activityobserved in glomeruli, suggests that activity normalization does occurbetween the glomerular and mitral cell responses. We show here thatglomerular neural networks in the olfactory bulb can perform thecomputations necessary to normalize patterns evoked by odorants atdifferent concentrations. Consequently, activation patterns at the outputof the olfactory bulb, conveyed by mitral cell spiking, would be betterable to preserve odor quality information across concentrations.Supported by NIDCD grant #DC005727 to TAC and NIDCD grant#DC006516 to ML.75