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General Introduction 12 S-transferases, and cytochrome P450. See Vogt et al. (1985) and Vogt et al. (2003) for reviews. 1.5.2 Membrane proteins Two classes of membrane proteins have been postulated to be of importance to moth olfaction, the first one being sensory neuron membrane proteins (SNMPs) and the other being odorant receptors. SNMPs were discovered in 1988 (Vogt et al., 1988; Rogers et al., 2001) in the antennal lymph of A. polyphemus. There are two classes of SNMPs (SNMP1 and SNMP2) in moths, with 25 to 75% amino acid identity between them (Vogt et al., 2003). They were thought to be candidates for the PR of moths due to their antennal specific expression, pheromone binding ability and expression onset synchronised with olfactory function development in moths (Vogt et al., 1988; Rogers et al., 2001a). This hypothesis was later rejected when evidence emerged that SNMPs were expressed in similar levels in both male and female antennae, had only two transmembrane domains, were found in most olfactory sensilla types and had low diversity (Rogers et al., 1997; Rogers et al., 2001). SNMPs are similar to mammalian membrane bound CD36 proteins. CD36 has implications in cell-to-cell interaction, in the transport of small hydrophobic molecules and binding protein/lipid complexes (Vogt et al., 2003). A study carried out by Benton et al. (2007) showed that SNMP is essential in pheromone induced response of PRs in D. melanogaster (Figure 1.3). SNMP is expressed in high concentrations in the trichoid sensilla of Drosophila but does not affect the development of trichoid OSNs and support cells. Several different pheromone binding experiments showed that Drosophila SNMP is essential for cVA mediated response of OR67d. H. virescens PR, HvOR13 when expressed in OR67d neurons also required SNMP to elicit response to the H. virescens pheromone component (Z)-11-hexadecenal. This study indicates a role of insect SNMPs as a co- receptor for pheromone reception, due to their preference for binding lipids (Benton et al., 2007). SNMP may function in olfactory perception of pheromones by interacting with different components of the olfactory system. It could be involved in destabilising the PBP/pheromone complex and acting as a preliminary receptor for the pheromone, conveying it to the PR. It could also couple to the signal transduction pathway or be involved in signal termination (Rogers et al., 2001; Vogt et al., 2003).
General Introduction 13 Figure 1.3: Model of insect pheromone detection demonstrating a role of SNMP in cVA mediated response of OR67d, as depicted by Benton et al. (2007). The SNMP may be acting as a preliminary receptor, destabilising the OBP/pheromone complex and conveying the pheromone to the PR for signal transduction to occur. Odorant receptors are seven transmembrane (7TM) domain proteins localised on the dendritic membranes of ORNs and detect odorants that enter the sensillum lymph (Benton, 2006). ORs function in binding odorants as they are transported to the dendritic membrane. This interaction sets off a signalling cascade causing the ORN to depolarise and a signal is relayed via the axonal end of the ORN to the antennal lobe in the brain. In contrast to the broadly tuned ORs, pheromone receptors in insects, like moths, are thought to be highly tuned to sex pheromones (Nakagawa et al., 2005; Mitsuno et al., 2008; Forstner et al., 2009; Wang et al., 2010). This represents the holy grail of the insect olfactory system in that the identification of PRs will give a better understanding of the underlying mechanisms of sex pheromone reception and pheromone controlled behaviours such as mating. 1.5.2.1 Odorant receptor identification in moths The first putative ORs to be identified in moths were from the tobacco budworm H. virescens using the basic local alignment search tool (BLAST) of Heliothis genomic
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Page 3 and 4: Abstract Abstract Olfaction or the
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4.1 Introduction 4 Identification o
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Identification of putative odorant
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Microarray OR 454 Transcriptome OR
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5.1 Introduction 5 Concluding Discu
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Concluding Discussion 131 against t
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Concluding Discussion 133 sequencin
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Appendix B 135 Buffered TB (Sambroo
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Appendix C 137 C. Appendix C - Clus
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Appendix D 139 D. Appendix D - Solu
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Appendix E 141 I II
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Appendix E 143 V
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Appendix E 145 VII continued Figure
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References 147 Ansebo, L., Ignell,
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References 149 Butenandt, A., Beckm
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References 151 Fedurco, M., Romieu,
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References 153 Große-Wilde, E., St
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References 155 Hrdy, I., F. Kuldova
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References 157 Kaissling, K. E. (19
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References 159 Krieger, J., Große-
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References 161 Lopez-Gomez, R. and
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References 163 Miura, N., Nakagawa,
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References 165 Pell, J. K., Macaula
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References 167 Røstelien, T., Stra
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References 169 Stowers, L. and Loga
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References 171 Turner, C. T., Davy,
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References 173 Vogt, R. G., Riddifo
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References 175 Widmayer, P., Heifet
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