Rudimentary expression of RYamide in Drosophila melanogaster relative to other Drosophila species points to a functional decline of this neuropeptide gene

Veenstra JA(1), Khammassi H(2).

Author information:
(1)INCIA, UMR 5287 CNRS, Université de Bordeaux, Pessac, France. Electronic address: .
(2)INCIA, UMR 5287 CNRS, Université de Bordeaux, Pessac, France.

RYamides are arthropod neuropeptides with unknown function. In 2011 two RYamides
were isolated from D. melanogaster as the ligands for the G-protein coupled
receptor CG5811. The D. melanogaster gene encoding these neuropeptides is highly
unusual, as there are four RYamide encoding exons in the current genome assembly,
but an exon encoding a signal peptide is absent. Comparing the D. melanogaster
gene structure with those from other species, including D. virilis, suggests that
the gene is degenerating. RNAseq data from 1634 short sequence read archives at
NCBI containing more than 34 billion spots yielded numerous individual spots that
correspond to the RYamide encoding exons, of which a large number include the
intron-exon boundary at the start of this exon. Although 72 different sequences
have been spliced onto this RYamide encoding exon, none codes for the signal
peptide of this gene. Thus, the RNAseq data for this gene reveal only noise and
no signal. The very small quantities of peptide recovered during isolation and
the absence of credible RNAseq data, indicates that the gene is very little
expressed, while the RYamide gene structure in D. melanogaster suggests that it
might be evolving into a pseudogene. Yet, the identification of the peptides it
encodes clearly shows it is still functional. Using region specific antisera, we
could localize numerous neurons and enteroendocrine cells in D. willistoni, D.
virilis and D. pseudoobscura, but only two adult abdominal neurons in
D. melanogaster. Those two neurons project to and innervate the rectal papillae,
suggesting that RYamides may be involved in the regulation of water homeostasis.

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