Insects use their antennae for smelling and thus for locating resources in their environment. In a new article, Max Planck researchers present the first complete analysis of genes involved in antennal olfaction of the tobacco hornworm Manduca sexta. Approximately 70 different receptors expressed in some 100,000 neurons allow these moths to detect a large number of odours and to perform relevant door-guided behaviours. This is the first more or less complete antennal transcriptome characterized in a non-model insect.
Insects have a highly sensitive sense of smell. Extremely low concentrations of door molecules in the air are sufficient to be detected by receptor neurons on their antennae. Specific proteins, so-called receptor proteins, expressed in these neurons recognize the doors. The door molecules bind to the receptors and produce chemical and electrical signals that are processed in the insect brain and eventually affect the insect's behaviour.
Apart from the receptors, further proteins involved in olfaction, including enzymes and chemosensory proteins, come into play. Based on these molecular principles, all insects follow their innate and elementary survival formula: finding food, recognizing mates, and − in case of females − identifying adequate oviposition sites that guarantee nutritious and easily digestible food for their offspring.
Moths (Lepidotera) are popular research objects in addition to fruit flies. The genome of the silkworm Bombyx mori has been fully sequenced. This insect, however, has been domesticated by humans for thousands of years, therefore its native conspecifics can no longer be found. On the other hand, the "habits" of the tobacco hornworm Manduca sexta, a moth species native to North America, have been the subject of intense physiological investigations to study the insect olfactory system, and recently also because its host plant, wild tobacco Nicotiana attenuata, has advanced to an important model plant in ecological research.
Genetic analysis of the Manduca sexta antennae closes a gap in the search after the insect's door-directed behaviour: The release of stress-induced door molecules by tobacco plants is well studied, as is the pollination of the flowers by the moths. "But how does the plant door -- metaphorically speaking − end up in the insect's brain?" asks Bill Hansson, director of the Department of Evolutionary Neuroethology founded in 2006 at the Max Planck Institute for Chemical Ecology.
The scientists identified the antennal transcriptome as an important basis for studying olfactory function of the insect and sequenced all active genes in the antennae completely. Additionally, they determined the amount of individual messenger RNAs (mRNAs) that belong to each gene. Sequence information which involved more than 66 million nucleotides was analyzed. Basically, the results can be summarized as follows:
The research was published in the Proceedings of the National Academy of Sciences.
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