Characterization of the chemosensory protein gene family from the Eastern spruce budworm, Choristoneura fumiferana

• Main Author: Wanner, Kevin W.
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/17326

The peripheral sensory system of insects is the first to detect chemical stimuli; it is composed of specialized sensory neurons located within hollow, hair-like sensilla. Chemosensory proteins (CSPs) and odorant binding proteins (OBPs) are small, soluble proteins that transport hydrophobic stimuli across the hydrophilic lymph that separates the sensory receptors from the external environment. Incidental results from various studies indicate that most CSPs, and some OBPs, are expressed broadly in many different tissues, raising the question 'what is their non-sensory function?' In this thesis I explored the nonsensory function of CSPs using three different scopes of investigation: 1) an in silico analysis of all known CSP sequences, 2) a characterization of the expression pattern of four CSP genes from a representative lepidopteran species, and 3) a functional characterization of an individual CSP. I identified 15 new CSP sequences; four from cDNA clones described herein and 11 from sequence databases. Several protein similarity classes, representing CSPs from six insect orders, were identified, and each was characterized by highly conserved sequence motifs, including (A) N-terminal YTTKYDN(V/I)(WD)(L/V)DEIL, (B) central DGKELKXX(I/L)PDAL, and, (C) C-terminal KYDP. Three similarity classes were identified that diverged from these conserved motifs, presumably because they are under new functional and selective pressures. A detailed analysis of the expression pattern of four CSP genes from the Eastern spruce budworm, Choristoneura fumiferana, revealed that one (characterized by the retention of the conserved motifs) was expressed in the adult stage, while two that diverged from the conserved motifs were expressed in the immature stages (larvae and pupae). Furthermore, two of the divergent CSP genes were up-regulated during a natural molt, or during an ecdysteroid agonist induced molt. The ligand binding specificity of CfumAY624538, a divergent CSP, was characterized using the fluorescent reporter 1-NPN. Some CSPs bind to medium chain-length fatty acids; this was not the case for CfumAY624538, rather, a short chain-length alcohol was the only ligand tested that displaced 1-NPN in competition. Collectively, my results indicate that divergent CSPs from the Eastern spruce budworm function in development, including larval molting. === Land and Food Systems, Faculty of === Graduate