Background: Diapause is a seasonal dormancy that allows organisms to survive unfavorable conditions and optimizes the timing of reproduction and growth. Emergence from diapause reverses the state of arrested development and metabolic suppression returning the organism to an active state. The physiological mechanisms that regulate the transition from diapause to post-diapause are still unknown. In this study, this transition has been characterized for the sub-arctic calanoid copepod Neocalanus flemingeri, a key crustacean zooplankter that supports the highly productive North Pacific fisheries. Transcriptional profiling of females, determined over a two-week time series starting with diapausing females collected from > 400m depth, characterized the molecular mechanisms that
regulate the post-diapause trajectory.
Results: A complex set of transitions in relative gene expression defined the transcriptomic changes from diapause to post-diapause. Despite low temperatures (5–6 °C), the switch from a “diapause” to a “post-diapause” transcriptional profile occurred within 12 h of the termination stimulus. Transcriptional changes signaling the end of diapause were activated within one-hour post collection and included the up-regulation of genes involved in the 20E cascade pathway, the TCA cycle and RNA metabolism in combination with the down-regulation of genes associated with chromatin silencing. By 12 h, females exhibited a post-diapause phenotype characterized by the up-regulation of genes involved in cell division, cell differentiation and multiple developmental processes. By seven days post collection, the reproductive program was fully activated as indicated by up-regulation of genes involved in oogenesis and energy metabolism, processes that were enriched among the differentially expressed genes.
Conclusions: The analysis revealed a finely structured, precisely orchestrated sequence of transcriptional changes that led to rapid changes in the activation of biological processes paving the way to the successful completion of the reproductive program. Our findings lead to new hypotheses related to potentially universal mechanisms that terminate diapause before an organism can resume its developmental program.
more »
« less
Temperature-dependent vitamin D signaling regulates developmental trajectory associated with diapause in an annual killifish
The mechanisms that integrate environmental signals into developmental programs remain largely uncharacterized. Nuclear receptors (NRs) are ligand-regulated transcription factors that orchestrate the expression of complex phenotypes. The vitamin D receptor (VDR) is an NR activated by 1α,25-dihydroxyvitamin D3[1,25(OH)2D3], a hormone derived from 7-dehydrocholesterol (7-DHC). VDR signaling is best known for regulating calcium homeostasis in mammals, but recent evidence suggests a diversity of uncharacterized roles. In response to incubation temperature, embryos of the annual killifish
- NSF-PAR ID:
- 10079766
- Publisher / Repository:
- Proceedings of the National Academy of Sciences
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 115
- Issue:
- 50
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- p. 12763-12768
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract In preparation for the onset of environmental challenges like overwintering, food limitation, anoxia, or water stress, many invertebrates and certain killifish enter diapause. Diapause is a developmentally‐programed dormancy characterized by suppression of development and metabolism. For embryos of
Artemia franciscana (brine shrimp), the metabolic arrest is profound. These gastrula‐stage embryos depress oxidative metabolism by ~99% during diapause and survive years of severe desiccation in a state termed anhydrobiosis. Trehalose is the sole fuel source for this developmental stage. Mitochondrial function during diapause is downregulated primarily by restricting substrate supply, as a result of inhibiting key enzymes of carbohydrate metabolism. Because proton conductance across the inner membrane is not decreased during diapause, the inference is that membrane potential must be compromised. In the absence of any intervention, the possibility exists that the F1FoATP synthase and the adenine nucleotide translocator may reverse, leading to wholesale hydrolysis of cellular ATP.Studies with anhydrobiotes like
A. franciscana are revealing multiple traits useful for improving desiccation tolerance that include the expression and accumulation late embryogenesis abundant (LEA) proteins and trehalose. LEA proteins are intrinsically disordered in aqueous solution but gain secondary structure (predominantly α‐helix) as water is removed. These protective agents stabilize biological structures including lipid bilayers and mitochondria during severe water stress. © 2018 IUBMB Life, 70(12):1251–1259, 2018 -
Collapsin response mediator protein-2 (CRMP2) in humans, UNC-33 in C. elegans , is a molecule that mediates axonal outgrowth and stability. UNC-33/CRMP2 has been hypothesized as a potential drug target for treating Alzheimer’s and other neurodegenerative diseases, which can often be attributed in part to aging. In aging, CRMP2 becomes hyperphosphorylated, which decreases the protein’s functionality, destabilizes the cellular skeleton, and contributes to neurodegeneration. In C. elegans, aging can be slowed by entering dauer diapause; a non-aging developmental stage turned on when the DAF-7/TGFβ signaling pathway is silenced in response to environmental stressors. In our laboratory, we discovered that unc-33 mutants are unable to form dauers in response to environmental stressors, but the mechanism behind this is still unknown. Here, we present a study that investigates whether a mutation in the daf-7 gene which leads to a temperature sensitive constitutive dauer phenotype can rescue phenotypes characteristic of unc-33 mutants. To this end, we created unc-33 ; daf-7 double mutants and quantified proper dauer formation after exposure to unfavorable environmental conditions. In addition, we tested how the introduction of the daf-7 mutation would affect the locomotion of the double mutants on an agar plate and a liquid medium. Furthermore, we examined axonal elongation of the double mutants using a transgene, juIs76, which expresses GFP in GABAergic motor neurons. Our analysis of unc-33; daf-7 double mutants showed that introducing the daf-7 mutation into an unc-33 mutant rescued dauer formation. However, further studies revealed that the unc-33; daf-7 double mutants had defects in axonal outgrowth of their D-type motor neuron which had been previously seen in unc-33 single mutants and impaired locomotion. Based on these results, we concluded that unc-33 mutants might have a problem suppressing DAF-7 signaling under unfavorable environmental conditions, leading to the activation of reproductive programs and the development of adults instead of dauers.more » « less
-
more » « less
Abstract Many arthropods undergo a seasonal dormancy termed “diapause” to optimize timing of reproduction in highly seasonal environments. In the North Atlantic, the copepod
Calanus finmarchicus completes one to three generations annually with some individuals maturing into adults, while others interrupt their development to enter diapause. It is unknown which, why and when individuals enter the diapause program. Transcriptomic data from copepods on known programs were analyzed using dimensionality reduction of gene expression and functional analyses to identify program-specific genes and biological processes. These analyses elucidated physiological differences and established protocols that distinguish between programs. Differences in gene expression were associated with maturation of individuals on the reproductive program, while those on the diapause program showed little change over time. Only two of six filters effectively separated copepods by developmental program. The first one included all genes annotated to RNA metabolism and this was confirmed using differential gene expression analysis. The second filter identified 54 differentially expressed genes that were consistently up-regulated in individuals on the diapause program in comparison with those on the reproductive program. Annotated to oogenesis, RNA metabolism and fatty acid biosynthesis, these genes are both indicators for diapause preparation and good candidates for functional studies. -
Diapause is a state of developmental arrest adopted in response to or in anticipation of environmental conditions that are unfavorable for growth. In many cases, diapause is facultative, such that animals may undergo either a diapause or a non-diapause developmental trajectory, depending on environmental cues. Diapause is characterized by enhanced stress resistance, reduced metabolism, and increased longevity. The ability to postpone reproduction until suitable conditions are found is important to the survival of many animals, and both vertebrate and invertebrate species can undergo diapause. The decision to enter diapause occurs at the level of the whole animal, and thus hormonal signaling pathways are common regulators of the diapause decision. Unlike other types of developmental arrest, diapause is programmed, such that the diapause developmental trajectory includes a pre-diapause preparatory phase, diapause itself, recovery from diapause, and post-diapause development. Therefore, developmental pathways are profoundly affected by diapause. Here, I review two conserved hormonal pathways, insulin/IGF signaling (IIS) and nuclear hormone receptor signaling (NHR), and their role in regulating diapause across three animal phyla. Specifically, the species reviewed are Austrofundulus limnaeus and Nothobranchius furzeri annual killifishes, Caenorhabditis elegans nematodes, and insect species including Drosophila melanogaster , Culex pipiens , and Bombyx mori . In addition, the developmental changes that occur as a result of diapause are discussed, with a focus on how IIS and NHR pathways interact with core developmental pathways in C. elegans larvae that undergo diapause.more » « less
