Metabolomics reveals novel insight on dormancy of aquatic invertebrate encysted embryos

Abstract

Numerous aquatic invertebrates survive harsh environments by displaying dormancy as encysted embryos. This study aimed at determining whether metabolomics could provide molecular insight to explain the “dormancy syndrome” by highlighting functional pathways and metabolites, hence offering a novel comprehensive molecular view of dormancy. We compared the metabolome of morphologically distinct dormant encysted embryos (resting eggs) and non-dormant embryos (amictic eggs) of a rotifer ( Brachionus plicatilis ). Metabolome profiling revealed ~5,000 features, 1,079 of which were annotated. Most of the features were represented at significantly higher levels in non-dormant than dormant embryos. A large number of features was assigned to putative functional pathways indicating novel differences between dormant and non-dormant states. These include features associated with glycolysis, the TCA and urea cycles, amino acid, purine and pyrimidine metabolism. Interestingly, ATP, nucleobases, cyclic nucleotides, thymidine and uracil, were not detected in dormant resting eggs, suggesting an impairment of response to environmental and internal cues, cessation of DNA synthesis, transcription and plausibly translation in the dormant embryos. The levels of trehalose or its analogues, with a role in survival under desiccation conditions, were higher in resting eggs. In conclusion, the current study highlights metabolomics as a major analytical tool to functionally compare dormancy across species.

Gene expression in diapausing rotifer eggs in response to divergent environmental predictability regimes

“…Trehalose is known to accumulate in diapausing cysts of Artemia 45 , 46 and in diapausing rotifer eggs when they enter anhydrobiosis 47 . Transcripts encoding for trehalose-6-phosphate synthase and for trehalose phosphate synthase enzymes have been detected in diapausing rotifer eggs, suggesting its biosynthesis in rotifers 23 , 25 , 34 G protein-coupled receptor signalling pathway (17/206) G protein-coupled receptors (GPCR) regulate signal transduction pathways and play diverse and pivotal roles in the physiology of insects, especially in resistance to adverse environmental conditions 48 . Interestingly, a GPCR receptor in the silkworm, B. mori , has been identified as a specific cell surface receptor for the diapause hormone (DH) 49 .…”

“…There is evidence of K + -mediated stimulation of aminoacyl-tRNA (aa-tRNA) synthetase activity in bacteria 54 and insects 55 , with an effect on diapause termination in the latter. Rozema et al 25 have shown high levels of aa-tRNA synthetases in diapausing compared to asexual eggs in Brachionus Ion transmembrane transport (16/147) Free ions in the cytosol restart the cell machinery by reactivating cellular enzymes 56 . Dumont et al 57 showed that cyst hatching in some anostraceans increased after the addition of mobile ion carriers.…”

“…There is evidence of K + -mediated stimulation of aminoacyl-tRNA (aa-tRNA) synthetase activity in bacteria 54 and insects 55 , with an effect on diapause termination in the latter. Rozema et al 25 have shown high levels of aa-tRNA synthetases in diapausing compared to asexual eggs in Brachionus…”

“…Subsequent to initiation, organisms enter the maintenance phase, which coincides with the greatest stress tolerance and the deepest dormancy, the intensity of each varying substantially between organisms 3,20 . While the molecular mechanisms of diapause initiation and maintenance have long attracted scientific attention and generated a considerable body of knowledge 2,[21][22][23][24][25] , the mechanisms of diapause termination remain unclear, probably in part due to the intrinsic variability associated with bet-hedging strategies 26 .…”

“…Once produced, diapausing eggs typically sink to the sediment of water bodies where they are able to persist under harsh environmental conditions such as drought, extreme temperatures, and salinity fluctuations 4,33 . Recently, some studies have developed genomic resources for B. plicatilis, contributing to the discovery of genes that are key for survival during diapause 23,25,[34][35][36] . These genes are related to processes maintaining the stability and the integrity of cell compartments and macromolecules during this metabolically arrested stage of the rotifer life cycle (for review see 1 ).…”