Mechanisms of Olfaction in Insects - ResearchSpace@Auckland ...
Mechanisms of Olfaction in Insects - ResearchSpace@Auckland ...
Mechanisms of Olfaction in Insects - ResearchSpace@Auckland ...
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Identification <strong>of</strong> putative odorant receptors from Epiphyas postvittana 84<br />
the sequences from a H. virescens cDNA library. This identified n<strong>in</strong>e OR genes <strong>in</strong> H.<br />
virescens and further screen<strong>in</strong>g <strong>of</strong> the genomic sequences as well as transcriptome<br />
sequenc<strong>in</strong>g have led to the identification <strong>of</strong> a total <strong>of</strong> 21 ORs <strong>in</strong> H. virescens so far<br />
(Krieger et al., 2004). ORs have also been identified from transcriptome sequences <strong>of</strong><br />
A. polyphemus, A. pernyi, and M. sexta. In B. mori, 68 ORs have been identified from<br />
transcriptome and genomic sequences, the highest number <strong>of</strong> ORs identified <strong>in</strong> a moth<br />
so far (Krieger et al., 2005; Nakagawa et al., 2005; Wanner et al., 2007; Tanaka et al.,<br />
2009). Degenerate PCR has also been used to identify moth ORs, for example,<br />
Mitsuno et al. (2008) identified 10 ORs from three different moth species us<strong>in</strong>g<br />
degenerate PCR. However, due to the highly divergent nature <strong>of</strong> ORs, with only 10-<br />
75% am<strong>in</strong>o acid sequence identity between and with<strong>in</strong> them, degenerate PCR has<br />
been least successful <strong>in</strong> identify<strong>in</strong>g new ORs, <strong>in</strong>dicat<strong>in</strong>g the need for more high<br />
throughput sequenc<strong>in</strong>g <strong>in</strong> order to identify more members <strong>of</strong> this highly divergent<br />
group.<br />
From glomeruli studies <strong>in</strong> mammals, it has been observed that each OSN very likely<br />
express only a s<strong>in</strong>gle OR. OSNs express<strong>in</strong>g the same OR are scattered throughout the<br />
epithelium, however they merge to the same glomerulus <strong>in</strong> the olfactory bulb. Hence a<br />
close estimation <strong>of</strong> the number <strong>of</strong> ORs <strong>in</strong> a given organism can be predicted from the<br />
number <strong>of</strong> glomeruli it possess. Glomeruli studies <strong>in</strong> tortricids have shown the<br />
presence <strong>of</strong> anywhere between 48 and 72 glomeruli (Masante-Roca et al., 2005;<br />
Varela et al., 2009). No glomeruli studies have yet been done <strong>in</strong> E. postvittana so the<br />
number <strong>of</strong> ORs could be anywhere between 48 and 72. From an EST library <strong>of</strong> male<br />
E. postvittana antennae, three ORs have been identified (Jordan et al., 2009) (refer to<br />
section 1.7 for more details). ORs and PRs are expressed at low levels <strong>in</strong> tissues<br />
therefore are under-represented <strong>in</strong> EST collections, especially <strong>in</strong> “shallow” Sanger<br />
based collections.