The contribution of the genomes of a termite and a locust to our understanding of insect neuropeptides and neurohormones
The genomes of the migratory locust Locusta migratoria and the termite
Zootermopsis nevadensis were mined for the presence of genes encoding
neuropeptides, neurohormones, and their G-protein coupled receptors (GPCRs). Both
species have retained a larger number of neuropeptide and neuropeptide GPCRs than
the better known holometabolous insect species, while other genes that in
holometabolous species appear to have a single transcript produce two different
precursors in the locust, the termite or both. Thus, the recently discovered CNMa
neuropeptide gene has two transcripts predicted to produce two structurally
different CNMa peptides in the termite, while the locust produces two different
myosuppressin peptides in the same fashion. Both these species also have a
calcitonin gene, which is different from the gene encoding the calcitonin-like
insect diuretic hormone. This gene produces two types of calcitonins, calcitonins
A and B. It is also present in Lepidoptera and Coleoptera and some Diptera, but
absent from mosquitoes and Drosophila. However, in holometabolous insect species,
only the B transcript is produced. Their putative receptors were also identified.
In contrast, Locusta has a highly unusual gene that codes for a salivation
stimulatory peptide. The Locusta genes for neuroparsin and vasopressin are
particularly interesting. The neuroparsin gene produces five different
transcripts, of which only one codes for the neurohormone identified from the
corpora cardiaca. The other four transcripts code for neuroparsin-like proteins,
which lack four amino acid residues, and that for that reason we called
neoneuroparsins. The number of transcripts for the neoneuroparsins is about 200
times larger than the number of neuroparsin transcripts. The first exon and the
putative promoter of the vasopressin genes, of which there are about seven copies
in the genome, is very well-conserved, but the remainder of these genes is not.
The relevance of these findings is discussed.