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Zajic DE, Podrabsky JE. GABA metabolism is crucial for long-term survival of anoxia in annual killifish embryos. J Exp Biol 2020; 223:jeb229716. [PMID: 32859669 DOI: 10.1242/jeb.229716] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Accepted: 08/24/2020] [Indexed: 08/25/2023]
Abstract
In most vertebrates, a lack of oxygen quickly leads to irreparable damages to vital organs, such as the brain and heart. However, there are some vertebrates that have evolved mechanisms to survive periods of no oxygen (anoxia). The annual killifish (Austrofundulus limnaeus) survives in ephemeral ponds in the coastal deserts of Venezuela and their embryos have the remarkable ability to tolerate anoxia for months. When exposed to anoxia, embryos of A. limnaeus respond by producing significant amounts of γ-aminobutyric acid (GABA). This study aims to understand the role of GABA in supporting the metabolic response to anoxia. To explore this, we investigated four developmentally distinct stages of A. limnaeus embryos that vary in their anoxia tolerance. We measured GABA and lactate concentrations across development in response to anoxia and aerobic recovery. We then inhibited enzymes responsible for the production and degradation of GABA and observed GABA and lactate concentrations, as well as embryo mortality. Here, we show for the first time that GABA metabolism affects anoxia tolerance in A. limnaeus embryos. Inhibition of enzymes responsible for GABA production (glutamate decarboxylase) and degradation (GABA-transaminase and succinic acid semialdehyde dehydrogenase) led to increased mortality, supporting a role for GABA as an intermediate product and not a metabolic end-product. We propose multiple roles for GABA during anoxia and aerobic recovery in A. limnaeus embryos, serving as a neurotransmitter, an energy source, and an anti-oxidant.
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Affiliation(s)
- Daniel E Zajic
- Department of Biology, Portland State University, PO Box 751, Portland, OR 97207, USA
- Health, Human Performance, and Athletics Department, Linfield University, 900 SE Baker, McMinnville, OR 97128, USA
| | - Jason E Podrabsky
- Department of Biology, Portland State University, PO Box 751, Portland, OR 97207, USA
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Dolfi L, Ripa R, Antebi A, Valenzano DR, Cellerino A. Cell cycle dynamics during diapause entry and exit in an annual killifish revealed by FUCCI technology. EvoDevo 2019; 10:29. [PMID: 31728179 PMCID: PMC6842169 DOI: 10.1186/s13227-019-0142-5] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2019] [Accepted: 10/17/2019] [Indexed: 12/31/2022] Open
Abstract
Background Annual killifishes are adapted to surviving and reproducing over alternating dry and wet seasons. During the dry season, all adults die and desiccation-resistant embryos remain encased in dry mud for months or years in a state of diapause where their development is halted in anticipation of the months that have to elapse before their habitats are flooded again. Embryonic development of annual killifishes deviates from canonical teleost development. Epiblast cells disperse during epiboly, and a “dispersed phase” precedes gastrulation. In addition, annual fish have the ability to enter diapause and block embryonic development at the dispersed phase (diapause I), mid-somitogenesis (diapause II) and the final phase of development (diapause III). Developmental transitions associated with diapause entry and exit can be linked with cell cycle events. Here we set to image this transition in living embryos. Results To visibly explore cell cycle dynamics during killifish development in depth, we created a stable transgenic line in Nothobranchius furzeri that expresses two fluorescent reporters, one for the G1 phase and one for the S/G2 phases of the cell cycle, respectively (Fluorescent Ubiquitination-based Cell Cycle Indicator, FUCCI). Using this tool, we observed that, during epiboly, epiblast cells progressively become quiescent and exit the cell cycle. All embryos transit through a phase where dispersed cells migrate, without showing any mitotic activity, possibly blocked in the G1 phase (diapause I). Thereafter, exit from diapause I is synchronous and cells enter directly into the S phase without transiting through G1. The developmental trajectories of embryos entering diapause and of those that continue to develop are different. In particular, embryos entering diapause have reduced growth along the medio-lateral axis. Finally, exit from diapause II is synchronous for all cells and is characterized by a burst of mitotic activity and growth along the medio-lateral axis such that, by the end of this phase, the morphology of the embryos is identical to that of direct-developing embryos. Conclusions Our study reveals surprising levels of coordination of cellular dynamics during diapause and provides a reference framework for further developmental analyses of this remarkable developmental quiescent state.
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Affiliation(s)
- Luca Dolfi
- 1Max Planck Institute for the Biology of Ageing, Cologne, Germany
| | - Roberto Ripa
- 2Bio@SNS, Scuola Normale Superiore, Pisa, Italy.,4Present Address: Max Planck Institute for the Biology of Ageing, Cologne, Germany
| | - Adam Antebi
- 1Max Planck Institute for the Biology of Ageing, Cologne, Germany
| | | | - Alessandro Cellerino
- 2Bio@SNS, Scuola Normale Superiore, Pisa, Italy.,3Leibniz Institute on Aging, Fritz Lipmann Institute, Jena, Germany
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Wagner JT, Knapp MJ, Podrabsky JE. Antioxidant capacity and anoxia-tolerance in Austrofundulus limnaeus embryos. J Exp Biol 2019; 222:jeb.204347. [DOI: 10.1242/jeb.204347] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 05/28/2019] [Indexed: 12/19/2022]
Abstract
Embryos of Austrofundulus limnaeus can tolerate extreme environmental stresses by entering into a state of metabolic and developmental arrest known as diapause. Oxidative stress is ubiquitous in aerobic organisms and the unique biology and ecology of A. limnaeus likely results in frequent and repeated exposures to oxidative stress during development. Antioxidant capacity of A. limnaeus was explored during development by measuring antioxidant capacity due to small molecules and several enzymatic antioxidant systems. Diapause II embryos can survive for several days in 1% hydrogen peroxide without indications of negative effects. Surprisingly, both small and large molecule antioxidant systems are highest during early development and may be due to maternal provisioning. Antioxidant capacity is largely invested in small molecules during early development and in enzymatic systems during late development. The switch in antioxidant mechanisms and decline in small molecule antioxidants during development correlates with the loss of extreme anoxia tolerance.
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Affiliation(s)
- Josiah T. Wagner
- Department of Biology, Portland State University, P.O. Box 751, Portland, OR 97207, USA
- Knight Cancer Institute Cancer Early Detection Advanced Research Center, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Mailcode: KR-CEDR, Portland, OR 97239, USA
| | - Michael J. Knapp
- Department of Biology, Portland State University, P.O. Box 751, Portland, OR 97207, USA
| | - Jason E. Podrabsky
- Department of Biology, Portland State University, P.O. Box 751, Portland, OR 97207, USA
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Temperature-dependent vitamin D signaling regulates developmental trajectory associated with diapause in an annual killifish. Proc Natl Acad Sci U S A 2018; 115:12763-12768. [PMID: 30446615 DOI: 10.1073/pnas.1804590115] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
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 Austrofundulus limnaeus can develop along two alternative trajectories: active development and diapause. These trajectories diverge early in development, from a biochemical, morphological, and physiological perspective. We manipulated incubation temperature to induce the two trajectories and profiled changes in gene expression using RNA sequencing and weighted gene coexpression network analysis. We report that transcripts involved in 1,25(OH)2D3 synthesis and signaling are expressed in a trajectory-specific manner. Furthermore, exposure of embryos to vitamin D3 analogs and Δ4-dafachronic acid directs continuous development under diapause-inducing conditions. Conversely, blocking synthesis of 1,25(OH)2D3 induces diapause in A. limnaeus and a diapause-like state in zebrafish, suggesting vitamin D signaling is critical for normal vertebrate development. These data support vitamin D signaling as a molecular pathway that can regulate developmental trajectory and metabolic dormancy in a vertebrate. Interestingly, the VDR is homologous to the daf-12 and ecdysone NRs that regulate dormancy in Caenorhabditis elegans and Drosophila We suggest that 7-DHC-derived hormones and their associated NRs represent a conserved pathway for the integration of environmental information into developmental programs associated with life history transitions in animals.
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Romney ALT, Podrabsky JE. Small noncoding RNA profiles along alternative developmental trajectories in an annual killifish. Sci Rep 2018; 8:13364. [PMID: 30190591 PMCID: PMC6127099 DOI: 10.1038/s41598-018-31466-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Accepted: 08/13/2018] [Indexed: 11/24/2022] Open
Abstract
Embryonic development of Austrofundulus limnaeus can occur along two phenotypic trajectories that are physiologically and biochemically distinct. Phenotype appears to be influenced by maternal provisioning based on the observation that young females produce predominately non-diapausing embryos and older females produce mostly diapausing embryos. Embryonic incubation temperature can override this pattern and alter trajectory. We hypothesized that temperature-induced phenotypic plasticity may be regulated by post-transcriptional modification via noncoding RNAs. As a first step to exploring this possibility, RNA-seq was used to generate transcriptomic profiles of small noncoding RNAs in embryos developing along the two alternative trajectories. We find distinct profiles of mature sequences belonging to the miR-10 family expressed in increasing abundance during development and mature sequences of miR-430 that follow the opposite pattern. Furthermore, miR-430 sequences are enriched in escape trajectory embryos. MiR-430 family members are known to target maternally provisioned mRNAs in zebrafish and may operate similarly in A. limnaeus in the context of normal development, and also by targeting trajectory-specific mRNAs. This expression pattern and function for miR-430 presents a potentially novel model for maternal-embryonic conflict in gene regulation that provides the embryo the ability to override maternal programming in the face of altered environmental conditions.
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Affiliation(s)
- Amie L T Romney
- Department of Biology, Portland State University, P.O. Box 751, Portland, OR, 97207, USA.
- Department of Anatomy, Physiology & Cell Biology, University of California at Davis School of Veterinary Medicine, One Shields Ave, Davis, CA, 95616, USA.
| | - Jason E Podrabsky
- Department of Biology, Portland State University, P.O. Box 751, Portland, OR, 97207, USA.
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Riggs CL, Podrabsky JE. Small noncoding RNA expression during extreme anoxia tolerance of annual killifish (Austrofundulus limnaeus) embryos. Physiol Genomics 2017; 49:505-518. [DOI: 10.1152/physiolgenomics.00016.2017] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Revised: 07/10/2017] [Accepted: 08/09/2017] [Indexed: 12/11/2022] Open
Abstract
Small noncoding RNAs (sncRNA) have recently emerged as specific and rapid regulators of gene expression, involved in a myriad of cellular and organismal processes. MicroRNAs, a class of sncRNAs, are differentially expressed in diverse taxa in response to environmental stress, including anoxia. In most vertebrates, a brief period of oxygen deprivation results in severe tissue damage or death. Studies on sncRNA and anoxia have focused on these anoxia-sensitive species. Studying sncRNAs in anoxia-tolerant organisms may provide insight into adaptive mechanisms supporting anoxia tolerance. Embryos of the annual killifish Austrofundulus limnaeus are the most anoxia-tolerant vertebrates known, surviving over 100 days at their peak tolerance at 25°C. Their anoxia tolerance and physiology vary over development, such that both anoxia-tolerant and anoxia-sensitive phenotypes comprise the species. This allows for a robust comparison to identify sncRNAs essential to anoxia-tolerance. For this study, RNA sequencing was used to identify and quantify expression of sncRNAs in four embryonic stages of A. limnaeus in response to an exposure to anoxia and subsequent aerobic recovery. Unique stage-specific patterns of expression were identified that correlate with anoxia tolerance. In addition, embryos of A. limnaeus appear to constitutively express stress-responsive miRNAs. Most differentially expressed sncRNAs were expressed at higher levels during recovery. Many novel groups of sncRNAs with expression profiles suggesting a key role in anoxia tolerance were identified, including sncRNAs derived from mitochondrial tRNAs. This global analysis has revealed groups of candidate sncRNAs that we hypothesize support anoxia tolerance.
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Affiliation(s)
- Claire L. Riggs
- Department of Biology, Portland State University, Portland, Oregon
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7
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Thompson AW, Furness AI, Stone C, Rade CM, Ortí G. Microanatomical diversification of the zona pellucida in aplochelioid killifishes. JOURNAL OF FISH BIOLOGY 2017; 91:126-143. [PMID: 28555871 DOI: 10.1111/jfb.13332] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Accepted: 04/12/2017] [Indexed: 06/07/2023]
Abstract
This study investigates zona pellucida (ZP) ultrastructure in fertilized eggs of annual killifishes (suborder Aplocheiloidei), a group of highly specialized fishes that are able to survive desiccation for several weeks to months before they hatch. Little is known about ZP or chorionic ultrastructure sustaining these life-history modes, so scanning electron microscopy (SEM) was used to describe this trait in a large number of aplocheiloids with a focus on the family Rivulidae and the genus Hypsolebias. New images of ZP ultrastructure for 52 aplocheiloid species are provided, more than doubling the number characterized thus far. The evolution of chorionic structure within this group is studied using these new data. Characters were coded into a morphological matrix and optimized onto a consensus phylogeny to assess phylogenetic signal and reconstruct ancestral character states. Although ZP characters seem highly homoplastic and exhibit a large amount of structural convergence among lineages, aplocheiloid killifishes have evolved a number of unique structures associated with the chorion. Some annual species seem to have lost long filaments because eggs are deposited in the soil instead of being adhered to aquatic plants.
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Affiliation(s)
- A W Thompson
- The George Washington University, Department of Biological Sciences, 2023 G St NW, Washington, D.C., 20052, U.S.A
| | - A I Furness
- University of California Irvine, Department of Biological Sciences, 321 Steinhaus Hall University of California Irvine, Irvine, CA, 92697, U.S.A
| | - C Stone
- The George Washington University, Department of Biological Sciences, 2023 G St NW, Washington, D.C., 20052, U.S.A
| | - C M Rade
- The George Washington University, Department of Biological Sciences, 2023 G St NW, Washington, D.C., 20052, U.S.A
| | - G Ortí
- The George Washington University, Department of Biological Sciences, 2023 G St NW, Washington, D.C., 20052, U.S.A
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8
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Woll SC, Podrabsky JE. Insulin-like growth factor signaling regulates developmental trajectory associated with diapause in embryos of the annual killifish Austrofundulus limnaeus. ACTA ACUST UNITED AC 2017; 220:2777-2786. [PMID: 28515235 DOI: 10.1242/jeb.151373] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 05/10/2017] [Indexed: 01/12/2023]
Abstract
Annual killifishes exhibit a number of unique life history characters including the occurrence of embryonic diapause, unique cell movements associated with dispersion and subsequent reaggregation of the embryonic blastomeres, and a short post-embryonic life span. Insulin-like growth factor (IGF) signaling is known to play a role in the regulation of metabolic dormancy in a number of animals but has not been explored in annual killifishes. The abundance of IGF proteins during development and the developmental effects of blocking IGF signaling by pharmacological inhibition of the insulin-like growth factor I receptor (IGF1R) were explored in embryos of the annual killifish Austrofundulus limnaeus Blocking of IGF signaling in embryos that would normally escape entrance into diapause resulted in a phenotype that was remarkably similar to that of embryos entering diapause. IGF-I protein abundance spikes during early development in embryos that will not enter diapause. In contrast, IGF-I levels remain low during early development in embryos that will enter diapause II. IGF-II protein is packaged at higher levels in escape-bound embryos compared with diapause-bound embryos. However, IGF-II levels quickly decrease and remain low during early development and only increase substantially during late development in both developmental trajectories. Developmental patterns of IGF-I and IGF-II protein abundance under conditions that would either induce or bypass entrance into diapause are consistent with a role for IGF signaling in the regulation of developmental trajectory and entrance into diapause in this species. We propose that IGF signaling may be a unifying regulatory pathway that explains the larger suite of characters that are associated with the complex life history of annual killifishes.
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Affiliation(s)
- S Cody Woll
- Department of Biology, Portland State University, PO Box 751, Portland, OR 97207, USA
| | - Jason E Podrabsky
- Department of Biology, Portland State University, PO Box 751, Portland, OR 97207, USA
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9
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Romney AL, Podrabsky JE. Transcriptomic analysis of maternally provisioned cues for phenotypic plasticity in the annual killifish, Austrofundulus limnaeus. EvoDevo 2017; 8:6. [PMID: 28439397 PMCID: PMC5401559 DOI: 10.1186/s13227-017-0069-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Accepted: 04/14/2017] [Indexed: 12/20/2022] Open
Abstract
Background Genotype and environment can interact during development to produce novel adaptive traits that support life in extreme conditions. The development of the annual killifish Austrofundulus limnaeus is unique among vertebrates because the embryos have distinct cell movements that separate epiboly from axis formation during early development, can enter into a state of metabolic dormancy known as diapause and can survive extreme environmental conditions. The ability to enter into diapause can be maternally programmed, with young females producing embryos that do not enter into diapause. Alternately, embryos can be programmed to “escape” from diapause and develop directly by both maternal factors and embryonic incubation conditions. Thus, maternally packaged gene products are hypothesized to regulate developmental trajectory and perhaps the other unique developmental characters in this species. Results Using high-throughput RNA sequencing, we generated transcriptomic profiles of mRNAs, long non-coding RNAs and small non-coding RNAs (sncRNAs) in 1–2 cell stage embryos of A. limnaeus. Transcriptomic analyses suggest maternal programming of embryos through alternatively spliced mRNAs and antisense sncRNAs. Comparison of these results to those of comparable studies on zebrafish and other fishes reveals a surprisingly high abundance of transcripts involved in the cellular response to stress and a relatively lower expression of genes required for rapid transition through the cell cycle. Conclusions Maternal programming of developmental trajectory is unlikely accomplished by differential expression of diapause-specific genes. Rather, evidence suggests a role for trajectory-specific splice variants of genes expressed in both phenotypes. In addition, based on comparative studies with zebrafish, the A. limnaeus 1–2 cell stage transcriptome is unique in ways that are consistent with their unique life history. These results not only impact our understanding of the genetic mechanisms that regulate entrance into diapause, but also provide insight into the epigenetic regulation of gene expression during development. Electronic supplementary material The online version of this article (doi:10.1186/s13227-017-0069-7) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Amie L Romney
- Department of Biology, Portland State University, P.O. Box 751, Portland, OR 97207 USA
| | - Jason E Podrabsky
- Department of Biology, Portland State University, P.O. Box 751, Portland, OR 97207 USA
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10
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Wagner JT, Herrejon Chavez F, Podrabsky JE. Mitochondrial DNA Sequence and Lack of Response to Anoxia in the Annual Killifish Austrofundulus limnaeus. Front Physiol 2016; 7:379. [PMID: 27630577 PMCID: PMC5005410 DOI: 10.3389/fphys.2016.00379] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2016] [Accepted: 08/17/2016] [Indexed: 12/14/2022] Open
Abstract
The annual killifish Austrofundulus limnaeus inhabits ephemeral ponds in regions of Venezuela, South America. Permanent populations of A. limnaeus are maintained by production of stress-tolerant embryos that are able to persist in the desiccated sediment. Previous work has demonstrated that A. limnaeus have a remarkable ability to tolerate extended periods of anoxia and desiccating conditions. After considering temperature, A. limnaeus embryos have the highest known tolerance to anoxia when compared to any other vertebrate yet studied. Oxygen is completely essential for the process of oxidative phosphorylation by mitochondria, the intracellular organelle responsible for the majority of adenosine triphosphate production. Thus, understanding the unique properties of A. limnaeus mitochondria is of great interest. In this work, we describe the first complete mitochondrial genome (mtgenome) sequence of a single adult A. limnaeus individual and compare both coding and non-coding regions to several other closely related fish mtgenomes. Mitochondrial features were predicted using MitoAnnotator and polyadenylation sites were predicted using RNAseq mapping. To estimate the responsiveness of A. limnaeus mitochondria to anoxia treatment, we measure relative mitochondrial DNA copy number and total citrate synthase activity in both relatively anoxia-tolerant and anoxia-sensitive embryonic stages. Our cross-species comparative approach identifies unique features of ND1, ND5, ND6, and ATPase-6 that may facilitate the unique phenotype of A. limnaeus embryos. Additionally, we do not find evidence for mitochondrial degradation or biogenesis during anoxia/reoxygenation treatment in A. limnaeus embryos, suggesting that anoxia-tolerant mitochondria do not respond to anoxia in a manner similar to anoxia-sensitive mitochondria.
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Affiliation(s)
- Josiah T Wagner
- Department of Biology, Center for Life in Extreme Environments, Portland State University Portland, OR, USA
| | - Florisela Herrejon Chavez
- Department of Biology, Center for Life in Extreme Environments, Portland State University Portland, OR, USA
| | - Jason E Podrabsky
- Department of Biology, Center for Life in Extreme Environments, Portland State University Portland, OR, USA
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11
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Podrabsky JE, Wilson NE. Hypoxia and Anoxia Tolerance in the Annual Killifish Austrofundulus limnaeus. Integr Comp Biol 2016; 56:500-9. [PMID: 27507238 DOI: 10.1093/icb/icw092] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Embryos of the annual killifish Austrofundulus limnaeus are routinely exposed to oxygen limitation during development and are extremely tolerant of anoxia. Importantly, tolerance of anoxia is not strictly associated with entrance into metabolic dormancy associated with diapause II, but rather any embryo will respond to anoxia by entering into a state of anoxia-induced quiescence. Hypoxia causes a reduction in the rate of development, reduced heart rates, and reduced capacities for metabolic enzyme activity in both aerobic and anaerobic pathways. Embryos of A. limnaeus begin life as oxyconformers, and transition into oxyregulators near the completion of embryonic development. As this transition occurs, extreme anoxia tolerance is lost. The rate of early development is independent of oxygen partial pressure, despite the fact that the embryos are oxyconformers. This suggests a contribution from anaerobic pathways to support early development. However, the specific pathways supporting this metabolism are unknown. The response of A. limnaeus embryos to hypoxia and anoxia is unique compared to other fishes and most other vertebrates, and thus future studies on this species may lend insight into novel mechanisms that support survival during prolonged oxygen limitation.
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Affiliation(s)
- Jason E Podrabsky
- Department of Biology, Portland State University, PO Box 751, Portland, OR 97207, USA
| | - Natalie E Wilson
- Department of Biology, Portland State University, PO Box 751, Portland, OR 97207, USA
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12
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The effects of hypoxia and temperature on metabolic aspects of embryonic development in the annual killifish Austrofundulus limnaeus. J Comp Physiol B 2014; 184:355-70. [PMID: 24510219 DOI: 10.1007/s00360-014-0803-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Revised: 12/30/2013] [Accepted: 01/13/2014] [Indexed: 10/25/2022]
Abstract
Embryos of Austrofundulus limnaeus are exceptional in their ability to tolerate prolonged bouts of complete anoxia. Hypoxia and anoxia are a normal part of their developmental environment. Here, we exposed embryos to a range of PO2 levels at two different temperatures (25 and 30 °C) to study the combined effects of reduced oxygen and increased temperature on developmental rate, heart rate, and metabolic enzyme capacity. Hypoxia decreased overall developmental rate and caused a stage-specific decline in heart rate. However, the rate of early development prior to the onset of organogenesis is insensitive to PO2. Increased incubation temperature caused an increase in the developmental rate at high PO2s, but hindered developmental progression under severe hypoxia. Embryonic DNA content in pre-hatching embryos was positively correlated with PO2. Citrate synthase, lactate dehydrogenase, and phosphoenolpyruvate carboxykinase capacity were all reduced in embryos developing under hypoxic conditions. Embryos of A. limnaeus are able to develop normally across a wide range of PO2s and contrary to most other vertebrates severe hypoxia is not a teratogen. Embryos of A. limnaeus do not respond to hypoxia through an increase in the capacity for enzymatic activity of the metabolic enzymes lactate dehydrogenase, citrate synthase, or phosphoenolpyruvate carboxykinase. Instead they appear to adjust whole-embryo metabolic capacity to match oxygen availability. However, decreased DNA content in hypoxia-reared embryos suggests that cellular enzymatic capacity may remain unchanged in response to hypoxia, and the reduced capacity may rather indicate reduced cell number in hypoxic embryos.
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Podrabsky JE, Menze MA, Hand SC. Long-Term survival of anoxia despite rapid ATP decline in embryos of the annual killifish Austrofundulus limnaeus. ACTA ACUST UNITED AC 2012; 317:524-32. [PMID: 22927170 DOI: 10.1002/jez.1744] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Revised: 05/11/2012] [Accepted: 06/05/2012] [Indexed: 01/24/2023]
Abstract
Embryos of the annual killifish Austrofundulus limnaeus can survive for months in the complete absence of oxygen. Survival of anoxia is associated with entry into a state of metabolic dormancy known as diapause. However, extreme tolerance of anoxia is retained for several days of post-diapause development. Rates of heat dissipation in diapause II and 4 days post-diapause II embryos were measured under aerobic conditions and during the transition into anoxia. Phosphorylated adenylate compounds were quantified in embryos during entry into anoxia and after 12 hr of aerobic recovery. Rates of heat dissipation were not affected by exposure to anoxia in diapause II embryos, while post-diapause II embryos experienced a profound decrease in heat dissipation. ATP decreased substantially in both developmental stages upon exposure to anoxia, and all indicators of cellular energetic status indicated energetic stress, at least based on the mammalian paradigm. The rate of decline in ATP is the most acute reported for any vertebrate. The mechanisms responsible for cellular survival despite a clear dysregulation between energy production and energy consumption remain to be identified. Necrotic and apoptotic cell death in response to hypoxia contribute to poor survival during many diseases and pathological conditions in mammals. Understanding the mechanisms that are in place to prevent maladaptive cell death in embryos of A. limnaeus may greatly improve treatment strategies in diseases that involve hypoxia and reperfusion injuries.
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Affiliation(s)
- Jason E Podrabsky
- Department of Biology, Portland State University, Portland, Oregon 97207-0751, USA.
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Meller CL, Meller R, Simon RP, Culpepper KM, Podrabsky JE. Cell cycle arrest associated with anoxia-induced quiescence, anoxic preconditioning, and embryonic diapause in embryos of the annual killifish Austrofundulus limnaeus. J Comp Physiol B 2012; 182:909-20. [PMID: 22570106 DOI: 10.1007/s00360-012-0672-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Revised: 04/18/2012] [Accepted: 04/20/2012] [Indexed: 01/19/2023]
Abstract
Embryos of the annual killifish Austrofundulus limnaeus can enter into dormancy associated with diapause and anoxia-induced quiescence. Dormant embryos are composed primarily of cells arrested in the G(1)/G(0) phase of the cell cycle based on flow cytometry analysis of DNA content. In fact, most cells in developing embryos contain only a diploid complement of DNA, with very few cells found in the S, G(2), or M phases of the cell cycle. Diapause II embryos appear to be in a G(0)-like state with low levels of cyclin D1 and p53. However, the active form of pAKT is high during diapause II. Exposure to anoxia causes an increase in cyclin D1 and p53 expression in diapause II embryos, suggesting a possible re-entry into the cell cycle. Post-diapause II embryos exposed to anoxia or anoxic preconditioning have stable levels of cyclin D1 and stable or reduced levels of p53. The amount of pAKT is severely reduced in 12 dpd embryos exposed to anoxia or anoxic preconditioning. This study is the first to evaluate cell cycle control in embryos of A. limnaeus during embryonic diapause and in response to anoxia and builds a foundation for future research on the role of cell cycle arrest in supporting vertebrate dormancy.
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Affiliation(s)
- Camie L Meller
- Department of Biology, Portland State University, P.O. Box 751, Portland, OR 97207-0751, USA
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15
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Podrabsky JE, Culpepper KM. Cell cycle regulation during development and dormancy in embryos of the annual killifish Austrofundulus limnaeus. Cell Cycle 2012; 11:1697-704. [PMID: 22531486 DOI: 10.4161/cc.19881] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Embryos of the annual killifish Austrofundulus limnaeus can enter into a state of metabolic dormancy, termed diapause, as a normal part of their development. In addition, these embryos can also survive for prolonged sojourns in the complete absence of oxygen. Dormant embryos support their metabolism using anaerobic metabolic pathways, regardless of oxygen availability. Dormancy in diapause is associated with high ATP and a positive cellular energy status, while anoxia causes a severe reduction in ATP content and large reductions in adenylate energy charge and ATP/ADP ratios. Most cells are arrested in the G 1/G 0 phase of the cell cycle during diapause and in response to oxygen deprivation. In this paper, we review what is known about the physiological and biochemical mechanisms that support metabolic dormancy in this species. We also highlight the great potential that this model holds for identifying novel therapies for human diseases such as heart attack, stroke and cancer.
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Affiliation(s)
- Jason E Podrabsky
- Department of Biology, Portland State University, Portland, OR, USA.
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16
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Pri-Tal BM, Blue S, Pau FKY, Podrabsky JE. Hormonal components of altered developmental pathways in the annual killifish, Austrofundulus limnaeus. Gen Comp Endocrinol 2011; 174:166-74. [PMID: 21906598 DOI: 10.1016/j.ygcen.2011.08.016] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Revised: 08/18/2011] [Accepted: 08/21/2011] [Indexed: 10/17/2022]
Abstract
The annual killifish, Austrofundulus limnaeus, typically enters embryonic diapause at two distinct points of development, termed diapause II and III. This study explores the role of maternal and embryonic steroid hormones, including 17-β-estradiol (E2), androstenedione (A4) and testosterone (T), in regulating the developmental decision to enter or escape diapause II. Steroid hormone levels were measured in tissues isolated from adult female killifish during the normal lifespan of this species and in individuals of the same age that were producing either high or low proportions of escape embryos. Levels of steroid hormones were also measured during early development and in fertilized eggs that were predicted to be on either an escape or diapausing developmental trajectory. Decreases in maternal E2 levels associated with age are correlated with decreasing escape embryo production. Maternal production of escape embryos is correlated with increased ratios of E2 to T in adult ovary tissue. Interestingly, neither hormone is significantly different in fish producing embryos on different developmental pathways when examined independently. Levels of steroid hormones in fertilized eggs are not correlated with entry or escape from diapause II, though levels of A4 tend to be higher in escape embryos. Escape embryos exhibit faster hormone metabolism and earlier hormone synthesis than embryos that will enter diapause II. Incubation of embryos in exogenous E2 is associated with a 7-fold increase in escape embryo production, and significantly elevated A4 levels. These data suggest that steroid hormones may be critical factors involved in determining developmental pathways in embryos of A. limnaeus.
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Affiliation(s)
- Benjamin M Pri-Tal
- Department of Biology, Portland State University, P.O. Box 751, Portland, OR 97207-0751, USA
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17
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Burggren WW, Reyna KS. Developmental trajectories, critical windows and phenotypic alteration during cardio-respiratory development. Respir Physiol Neurobiol 2011; 178:13-21. [PMID: 21596160 DOI: 10.1016/j.resp.2011.05.001] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Revised: 05/02/2011] [Accepted: 05/03/2011] [Indexed: 02/07/2023]
Abstract
Embryo-environment interactions affecting cardio-respiratory development in vertebrates have been extensively studied, but an equally extensive conceptual framework for interpreting and interrelating these developmental events has lagged behind. In this review, we consider the conceptual constructs of "developmental plasticity", "critical windows", "developmental trajectory" and related concepts as they apply to both vertebrate and invertebrate development. Developmental plasticity and the related phenomenon of "heterokairy" are considered as a subset of phenotypic plasticity, and examples of cardiovascular, respiratory and metabolic plasticity illustrate the variable outcomes of embryo-environment interactions. The concept of the critical window is revealed to be overarching in cardio-respiratory development, and events originating within a critical window, potentially mitigated by "self-repair" capabilities of the embryo, are shown to result in modified developmental trajectories and, ultimately, modified adult phenotype. Finally, epigenetics, fetal programming and related phenomena are considered in the context of potentially life-long cardio-respiratory phenotypic modification resulting from embryo-environment interactions.
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Affiliation(s)
- Warren W Burggren
- Developmental Integrative Biology Cluster, Department of Biological Sciences, University of North Texas, Denton, TX 76203-5017, USA.
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18
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Podrabsky JE, Garrett IDF, Kohl ZF. Alternative developmental pathways associated with diapause regulated by temperature and maternal influences in embryos of the annual killifish Austrofundulus limnaeus. J Exp Biol 2010; 213:3280-8. [PMID: 20833920 PMCID: PMC2936969 DOI: 10.1242/jeb.045906] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/22/2010] [Indexed: 11/20/2022]
Abstract
Embryos of the annual killifish Austrofundulus limnaeus enter a state of developmental arrest termed diapause as part of their normal developmental program. Diapause can occur at two distinct developmental stages in this species, termed diapause II and III. When incubated at 25°C, most embryos enter diapause II, whereas a small percentage of 'escape' embryos develop continuously past diapause II and enter diapause III. Control of entry into diapause II can be altered by maternal influences and the incubation environment experienced by the embryos. Young females produce a higher proportion of escape embryos than do older females. In addition, increasing the incubation temperature from 25 to 30°C induces all embryos to escape from diapause. Surprisingly, escape embryos follow a different morphological and physiological developmental trajectory than do embryos that enter diapause II. Development of anterior structures is advanced compared with that of posterior structures in escape embryos when compared with embryos that will enter diapause II. The difference in timing of development for these two trajectories is consistent with changes observed between two species but is very atypical of variation observed within a species. Importantly, the two developmental pathways diverge early in development, during the segmentation period, when, according to evolutionary theory, constraint on developmental pathways should be relatively high. The possession of alternative developmental pathways in a vertebrate embryo is a novel finding, the ecological and evolutionary importance of which is still unknown, but potentially significant in terms of life-history evolution.
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Affiliation(s)
- Jason E Podrabsky
- Department of Biology, Portland State University, PO Box 751, Portland, OR 97207-0751, USA.
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