Data from: Two cGMP-dependent protein kinases have opposing effects on molt-inhibiting hormone regulation of Y-organ ecdysteroidogenesis

Decapod crustaceans regulate molting through steroid molting hormones,
ecdysteroids, synthesized by the molting gland (Y-organ, YO).
Molt-inhibiting hormone (MIH), a neuropeptide synthesized and secreted by
the eyestalk ganglia, negatively regulates YO ecdysteroidogenesis. MIH
signaling is mediated by cyclic nucleotide second messengers.
cGMP-dependent protein kinase (PKG) is the presumed effector of MIH
signaling by inhibiting mechanistic Target of Rapamycin Complex 1
(mTORC1)-dependent ecdysteroidogenesis. Phylogenetic analysis of PKG
contiguous sequences in CrusTome as well as 35 additional species in NCBI
RefSeq, identified 206 PKG1 sequences in 108 species and 59 PKG2 sequences
in 53 species. These included four PKG1α splice variants in the N-terminal
region that were unique to decapods, as well as PKG1β and PKG2 homologs.
In vitro assays using YOs from the blackback land crab (Gecarcinus
lateralis) and green shore crab (Carcinus maenas) determined the effects
of MIH ± PKG inhibitors on ecdysteroid secretion. A general PKG inhibitor,
Rp-8-Br-PET-cGMPS, countered the effects of MIH, as ecdysteroid secretion
increased in PKG-inhibited YOs compared to C. maenas YOs incubated with
MIH alone. By contrast, a PKG2-specific inhibitor, AP-C5
(4-[4-(1H-Imidazol-1-yl)phenyl]-N-2-propyn-1-yl-2-pyrimidinamine),
enhanced the effects of MIH, as ecdysteroid secretion decreased in G.
lateralis and C. maenas YOs incubated with AP-C5 and MIH compared to YOs
incubated with MIH alone. These data suggest that both PKG1 and PKG2 are
activated by MIH, but have opposing effects on mTORC1-dependent
ecdysteroidogenesis. A model is proposed in which the dominant role of
PKG1 is countered by PKG2, resulting in low ecdysteroid production by the
basal YO during intermolt.