Serotonin modulation of caudal photoreceptor in crayfish

Transcriptional identification of genes light-interacting in the extraretinal photoreceptors of the crayfish Procambarusclarkii

Crayfish serve as a model for studying the effect of environmental lighting on locomotor activity and neuroendocrine functions. The effects of light on this organism are mediated differentially by retinal and extraretinal photoreceptors located in the cerebroid ganglion and the pleonal nerve cord. However, some molecular aspects of the phototransduction cascade in the pleonal extraretinal photoreceptors remain unknown. In this study, transcriptome data from the pleonal nerve cord of the crayfish Procambarusclarkii (Girard,1852) were analyzed to identify transcripts that potentially interact with phototransduction process. The Illumina MiSeq System and the pipeline Phylogenetically Informed Annotation (PIA) were employed, which places uncharacterized genes into pre-calculated phylogenies of gene families. Here, for the first time 62 transcripts identified from the pleonal nerve cord that are related to light-interacting pathways are reported; they can be classified into the following 11 sets: 1) retinoid pathway in vertebrates and invertebrates, 2) photoreceptor specification, 3) rhabdomeric phototransduction, 4) opsins 5) ciliary phototransduction, 6) melanin synthesis, 7) pterin synthesis, 8) ommochrome synthesis, 9) heme synthesis, 10) diurnal clock, and 11) crystallins. Moreover, this analysis comparing the sequences located on the pleonal nerve cord to eyestalk sequences reported in other studies reveals 94-100% similarity between the 55 common proteins identified. These results show that both retinal and pleonal non-visual photoreceptors in the crayfish equally expressed the transcripts involved in light detection. Moreover, they suggest that the genes related to ocular and extraocular light perception in the crayfish P.clarkii use biosynthesis pathways and phototransduction cascades commons.

Identification of putative amine receptor complement in the eyestalk of the crayfish, Procambarus clarkii

In decapod crustaceans, the amines dopamine, octopamine, serotonin, and histamine are known to serve as locally released and/or circulating neuromodulators. While many studies have focused on determining the modulatory actions of amines on decapod nervous systems, comparatively little is known about the identity of the receptors through which they exert their actions. Here, a crayfish, Procambarus clarkii, tissue-specific transcriptome was used to identify putative amine receptors in the eyestalk, a structure composed largely of the eyestalk ganglia, including the neuroendocrine X-organ-sinus gland system, and retina. Transcripts encoding 17 distinct putative amine receptors, three dopamine (one dopamine 1-like, one dopamine 2-like, and one dopamine/ecdysteroid-like), five octopamine (one alpha-like, three beta-like, and one octopamine/tyramine-like), three serotonin (two type-1-like and one type-7-like), and six histamine (five histamine-gated chloride channel A-like and one histamine-gated chloride channel B-like) were identified in the assembly. Comparison of the nucleotide sequence of the transcript encoding one predicted type-1-like serotonin receptor with that cloned previously from the P. clarkii nervous system shows the two sequences to be essentially identical, providing increased support for the validity of the transcripts used to deduce the proteins reported here. Reciprocal BLAST and structural/functional domain analyses support the protein family annotations ascribed to the putative P. clarkii receptors. These data represent the first large-scale description of amine receptors from P. clarkii, and as such provide a new resource for initiating gene-based studies of aminergic control of physiology/behavior at the level of receptors in this species.