| dc.description.abstracteng | Olfaction, the detection of odors is pivotal for insects, since it leads them to food sources or mating partners and triggers important behaviors. For the detection of pheromones, CD36-related sensory neuron membrane proteins (SNMPs) play a crucial role. Despite their necessity, the functional role of SNMPs is not yet fully understood. Generally, two single SNMPs, namely SNMP1 and SNMP2, have been described in insects, whereas the pest beetle Tribolium castaneum has six genes expressed that encode putative SNMPs as indicated by transcriptome analysis.
To investigate these proteins in more detail, I determined the actual full-length transcript sequences of the six T. castaneum SNMPs by RACE-PCR on antennal cDNA pools. This enabled the identification of the actual TcSNMP protein sequences and allowed the phylogenetic classification of these proteins. To analyze the expression patterns of the T. castaneum SNMPs, I established a reliable double fluorescence in situ hybridization protocol for adult antennae of T. castaneum, which I used to visualize and characterize the TcSNMP-expressing cells. This revealed that – besides TcSNMP2 for which no specific expression pattern could be determined - the TcSNMPs are expressed differently with regard to number of cells, antennal segments, as well as cell types, which suggests a distinct role of the diversified TcSNMPs. In addition, by loss-of-function experiments it became apparent that the neuronal TcSNMPs are involved in the detection of fatty odors, emitted from various ecological important sources, such as pheromones, social odors, as well as potential food odors. These findings extend the known involvement of SNMPs for pheromone detection to other odors apart from pheromones.
Moreover, functional analyses of heterologously expressed TcSNMPs in snmp1 mutant D. melanogaster showed that the beetle TcSNMPs were not able to complement lacking DmSNMP1 function. This indicated that the diversified beetle TcSNMPs evolved differentially to the fly DmSNMP1, to probably serve different functions. Remarkably, instead of rescuing the snmp1 mutant situation, some TcSNMPs modified the odor response profile of the pheromone detecting neurons of D. melanogaster towards non-pheromone odors. This implicates that SNMPs have functions in addition to the known mediation of pheromones.
Heterologous expression of DmSNMP2 isoform B and C in snmp1 mutant D. melanogaster with subsequent functional analyses revealed that the DmSNMP2 isoform B, but not isoform C, is able to rescue the snmp1 mutant situation. Via protein prediction tools I calculated the tertiary structure of these isoforms, which pointed to a particular alpha helix forming the functional region. The DmSNMP1 protein contains a corresponding alpha helix which offers the great opportunity for elucidating this putative functional area of DmSNMP1 in further analyses. | de |