Characterization of cyclic nucleotide phosphodiesterases in the transcriptome of the crustacean molting gland
Date
2019
Authors
Rifai, Nada Mukhtar, author
Mykles, Donald L., advisor
Garrity, Deborah, committee member
Kanatous, Shane, committee member
Di Pietro, Santiago, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Molting in crustaceans is a complex physiological process that has to occur in order for the animal to grow. The old exoskeleton must be discarded and a new one to be formed from the inside out. Molting is coordinated and regulated mainly by two hormones; steroid hormones named ecdysteroids, which are synthesized and secreted from a pair of Y- organs (YOs) that are located in the cephalothorax and a neuropeptide hormone, the molt inhibiting hormone (MIH), which is secreted from the X-organ/sinus gland complex located in the eyestalks. Molting is induced when MIH is decreased in the blood (hemolymph) which in turn stimulates the YOs to produce and secrete ecdysteroids (molting hormones). There are four distinctive physiological states that the YO can be in throughout the molt cycle; the transition of the YO from the "basal" to the "activated" state happens when the animal enters premolt. During mid-premolt, the YO transitions to the "committed" state, in which the YO becomes insensitive to MIH. In this state, the circulating hemolymph contains high levels of ecdysteroids, which increase to a peak before the actual molt (ecdysis) happens. The YO transitions from the committed to the repressed state in late premolt. Finally, the YO returns back to the basal state in the postmolt stage. MIH binds to membrane receptors, activating a signal transduction pathway divided into "triggering" and "summation" phases. A transient increase in cAMP during the triggering phase leads to prolonged cGMP-dependent suppression of ecdysteroidogenesis during the summation phase. This allows for sustained inhibition of the YO between MIH pulses in the intermolt animal. Cyclic nucleotide phosphodiesterases (PDEs) play an important role by controlling cAMP and cGMP levels. PDEs hydrolyze the phosphodiester bond in cAMP and cGMP to AMP and GMP, respectively. Mammals have 21 PDE genes that are categorized into 11 families, designated PDE1 to PDE11. Each PDE family has specific catalytic and biochemical properties and tissue distributions. Eight contigs encoding full-length PDE sequences were identified in the G. lateralis Y-organ transcriptome. Seven contigs encoding four full-length PDE sequences and three contigs encoding partial-length PDE were identified in the Carcinus maenas transcriptome. Multiple sequence alignments showed high sequence identities with orthologs from other species in catalytic (PDEase) and other conserved functional domains. Sequence analysis assigned the Gl-PDE sequences and Cm-PDE sequences to PDE1, PDE2, PDE3, PDE4, PDE5, PDE7, PDE8, PDE9, and PDE11 classes, indicating a high diversity of PDE genes in decapod crustaceans. The reduced sensitivity to MIH by the committed YO is associated with a large increase in PDE activity, which suggests that PDEs modulate the response to neuropeptide during the molt cycle. Non-hydrolyzable analogs of cAMP and cGMP inhibit YO ecdysteroid secretion in-vitro. Moreover, C. maenas YO ecdysteroidogenesis is inhibited by IBMX, a general PDE inhibitor, and Zaprinast, a specific PDE5 inhibitor. Rolipram, a specific PDE4 inhibitor, has no effect. These data suggest that PDE5 activity modulates the effect of MIH on YO ecdysteroidogenesis. RNA-seq data from MLA showed different mRNA levels for the different PDEs; PDE1 and PDE2 showed a similar pattern as they both increased in intermolt (IM) then decreased dramatically in early premolt (EP), mid premolt (MP), late premolt (LP), and post molt (PM). PDE4 increased in IM followed by a slight decrease and increase in EP and MP then a sharp decline in both LP and PM. Both PDE5 and PDE9 were similar in terms they increased in IM followed by a sharp decrease in EP, MP, LP and they differed as PDE5 increased slightly in PM whereas PDE9 remained decreased. PDE7 began with an increase in IM then a decline with a constant expression level in both EP and MP followed by dramatic decline in LP and PM. PDE11 showed a typical pattern consistent with the ecdysteroid expression level as it began with a slight increase in IM followed by an increased in EP and reached a peak in MP then declined in a dramatic way in LP and continued decreasing in PM. Taken together, the data suggest that PDE5 and PDE11 play a role in regulating cyclic nucleotide levels in the YO.
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Subject
molting
transcriptome
crustacean
YO
phosphodiestersases