Function-specific transcription in the nervous system and sense organs of insects

M. Gewecke, O. Franz, G. Schramm & T. Roeder

Zoologisches Inst., Neurophysiologie, Univ. Hamburg, Martin-Luther-King-Platz 3, 20146 Hamburg, Germany

The brain and sensory systems of both vertebrates and invertebrates could be structurally ad functionally devided into different parts. The parts of the brain, e.g. the optic lobe of insects, have different functional roles, in this case the processing of visual information. Most of these specific abilities rely on the expression of specific proteins. The knowledge of these proteins should allow a deeper understanding of the brain in general. Insect systems are less complex than the respective systems of vertebrates, making the analysis of function-specific transcription in insects preferable. We choose the desert locust (Schistocerca gregaria F.) as experimental animal, and a modified differential display PCR approach for m-RNA analysis (Liang, P., Pardee, A.B., 1992, Science 257: 967; Franz, O., Roeder, T., Gewecke, M., 1998, J. Comp. Physiol. 182: 627). By this DD-PCR method about 60 differentially expressed mRNAs could be identified in either of the tissues mentioned above. In the optic lobes and retinae a gene coding for a glutathione-S-transferase was described that might be required to protect these tissues against photo-induced radicals. Another mRNA found in the optic lobes only in young adults represents a centrosomin, the first one analysed in insects. This could be required for cell division and, therefore, can serve as a marker for neurogenesis in the insect brain. Within the antennae there are various specifically expressed transcripts. One of them hybridizes with three different transcripts almost exclusively found in the antennae. Expression in male antennae is at least two orders of magnitude higher compared with female antennae. One of these transcripts is not present in females. Interestingly, the smallest of the antennae-specific transcripts is also expressed in the optic lobes. Sequence analysis revealed no significant homology to known sequences, especially those for Pheromone or odorant binding proteins. This led to the attemption that it is a new type of sex-specific protein in the insect olfactory system. The largest number of differentially transcribed RNA's could be identified in the thoracic ganglia. Among them are several putative neuropeptide precursors, and also transcription factors belonging to either the zinc-finger or leucine zipper family. Supported by the DFG (Ge 249)

Index terms: Schistocerca gregaria F., diff. display PCR, mRNA, gene expression.

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