A novel form of pigment‐dispersing hormone in the central nervous system of the intertidal marine isopod, Eurydice pulchra (leach)

Abstract

Pigment-dispersing factor (PDF) is well known as a circadian clock output factor, which drives daily activity rhythms in many insects. The role of its homologue, pigment-dispersing hormone (PDH), in the regulation of circadian and/or circatidal rhythmicity in crustaceans is, however, poorly understood. The intertidal isopod crustacean, Eurydice pulchra has well-defined circatidal (12.4-hour) activity rhythms. In this study we show that this runs parallel to a circadian (24-hour) cycle of chromatophore dispersion. As a first step in determining the potential role of PDH in these rhythms, we have identified a novel form of PDH expressed in this species. Because conventional homology cloning was unsuccessful, we employed immuno-identification and Edman microsequencing to determine the primary structure of this peptide. From this, cDNA cloning identified the nucleotide encoding sequence and thus facilitated description of PDH neurons by in situ hybridization and immunohistochemistry. We show them to be morphologically similar to those that co-ordinate circadian activity rhythms in insects. In animals expressing both tidal (activity) and circadian (chromatophore) rhythms, however, there was no evidence for a corresponding periodicity in the expression of pdh transcript, as determined by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) in Eurydice heads. It is therefore suggested that any role for PDH in daily/tidal timing in Eurydice is not mediated at the transcriptional level, rather rhythms in neurohemal release may be important in such co-ordination.

Transcriptome and Peptidome Characterisation of the Main Neuropeptides and Peptidic Hormones of a Euphausiid: The Ice Krill, Euphausia crystallorophias

“…These seem to be specific to the Euphausiacea , and are described for the first time in this study. Their expression levels were significantly lower than those for PDHβ [100], [105], [106].…”

“…The most highly expressed members of PDH in other species are also PDHβ. Two isoforms exist, but these were not identified in krill [63], [101]–[105]. However, in E. crystallorophias , two long isoforms (PDHLβ I and II) co-exist with an α long form.…”

Dissociation of Circadian and Circatidal Timekeeping in the Marine Crustacean Eurydice pulchra

“…When we collapsed the dorsolateral cell data into daytime versus nighttime intensity, there was significantly higher EpPER intensity at night but not for the lateral cells (F 1,116  = 4.7, p = 0.031, and F 1,45  = 0.77, p = 0.39, respectively; Figure 3E). Finally, we compared the location of these putative circadian clock cells with the previously identified Eurydice PDH cells [17], a marker for a subset of circadian neurons in D. melanogaster [18]. It was clear that the EpPER-expressing cells were not the PDF-positive neurons.…”

“…As Epper does not show mRNA cycles, the modest but characteristic EpPER cycle detected by the anti-EpPER serum observed in the two groups of neurons in each hemisphere would presumably be generated posttranscriptionally, perhaps as a reduction in EpPER stability during the light phase of the cycle, as occurs in Drosophila [28]. In common with other insects [29–31], and in contrast to Drosophila , these PER-ir cells were not PDH-positive cells [17]. In addition, as noted in several insects, including the silkmoth, Antheraea pernyi , which has eight PER-ir cells, EpPER-ir was mainly cytoplasmic with only weak nuclear signal [24, 31].…”

Circadian cycles are the dominant transcriptional rhythm in the intertidal musselMytilus californianus

“…We do not know the extent to which either the circadian or tidal transcriptional rhythms observed in our data are entrained and will persist in the absence of external cues. A number of intertidal organisms, particularly crustaceans, display entrained behavioral rhythms that follow persistent circadian (28) and tidal patterns (29,30) even when held under constant conditions. Similarly, mussels are reported to show entrained tidal patterns of cell division (31).…”