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• 1. [Article] Alternate Developmental Pathways

  Chapter from the book, Annual Fishes: Life History Strategy, Diversity, and Evolution -- the first comprehensive reference on current knowledge of diverse species that exhibit unique survival strategies ...

  Citation × Citation Citation Abstract Copy Title: Alternate Developmental Pathways Author: Podrabsky, Jason E., Romney, Amie L., Culpepper, Kristin M. Year: 2015 Chapter from the book, Annual Fishes: Life History Strategy, Diversity, and Evolution -- the first comprehensive reference on current knowledge of diverse species that exhibit unique survival strategies and provide important models for basic and applied research. This work fills a void, covering the life cycle, reproductive biology, evolutionary ecology, reproductive behavior, sexual selection, genetics, speciation, and integrative and conservation strategies of annual fishes. Bringing together researchers in different areas of annual fishes to summarize previous work, overview the current research, and highlight promising areas of research, the book is organized into three sections focusing on: Diversity, life history, and reproductive biology Ecology and conservation Evolution The book provides a thorough understanding of the complexity of annual fishes and emphasizes their usefulness as a unique model organism for studies in vertebrate biology, particularly in areas such as speciation and senescence. It also notes the gaps in knowledge that challenge future research and encourages the continued expansion and development of research studies on annual fishes to address these gaps so that general vertebrate biology can be better understood. It serves as a valuable resource for scientists in a range of disciplines such as ichthyology, zoology, developmental and evolutionary biology, molecular biology and genetics, and ecology. Title: Alternate Developmental Pathways Author: Podrabsky, Jason E., Romney, Amie L., Culpepper, Kristin M. Year: 2015 Chapter from the book, Annual Fishes: Life History Strategy, Diversity, and Evolution -- the first comprehensive reference on current knowledge of diverse species that exhibit unique survival strategies and provide important models for basic and applied research. This work fills a void, covering the life cycle, reproductive biology, evolutionary ecology, reproductive behavior, sexual selection, genetics, speciation, and integrative and conservation strategies of annual fishes. Bringing together researchers in different areas of annual fishes to summarize previous work, overview the current research, and highlight promising areas of research, the book is organized into three sections focusing on: Diversity, life history, and reproductive biology Ecology and conservation Evolution The book provides a thorough understanding of the complexity of annual fishes and emphasizes their usefulness as a unique model organism for studies in vertebrate biology, particularly in areas such as speciation and senescence. It also notes the gaps in knowledge that challenge future research and encourages the continued expansion and development of research studies on annual fishes to address these gaps so that general vertebrate biology can be better understood. It serves as a valuable resource for scientists in a range of disciplines such as ichthyology, zoology, developmental and evolutionary biology, molecular biology and genetics, and ecology. Close

• 2. [Article] Tolerance of Environmental Stress

  Chapter from the book, Annual Fishes: Life History Strategy, Diversity, and Evolution -- the first comprehensive reference on current knowledge of diverse species that exhibit unique survival strategies ...

  Citation × Citation Citation Abstract Copy Title: Tolerance of Environmental Stress Author: Podrabsky, Jason E., Riggs, Claire L., Wagner, Josiah Tad Year: 2015 Chapter from the book, Annual Fishes: Life History Strategy, Diversity, and Evolution -- the first comprehensive reference on current knowledge of diverse species that exhibit unique survival strategies and provide important models for basic and applied research. This work fills a void, covering the life cycle, reproductive biology, evolutionary ecology, reproductive behavior, sexual selection, genetics, speciation, and integrative and conservation strategies of annual fishes. Bringing together researchers in different areas of annual fishes to summarize previous work, overview the current research, and highlight promising areas of research, the book is organized into three sections focusing on: Diversity, life history, and reproductive biology Ecology and conservation Evolution The book provides a thorough understanding of the complexity of annual fishes and emphasizes their usefulness as a unique model organism for studies in vertebrate biology, particularly in areas such as speciation and senescence. It also notes the gaps in knowledge that challenge future research and encourages the continued expansion and development of research studies on annual fishes to address these gaps so that general vertebrate biology can be better understood. It serves as a valuable resource for scientists in a range of disciplines such as ichthyology, zoology, developmental and evolutionary biology, molecular biology and genetics, and ecology. Title: Tolerance of Environmental Stress Author: Podrabsky, Jason E., Riggs, Claire L., Wagner, Josiah Tad Year: 2015 Chapter from the book, Annual Fishes: Life History Strategy, Diversity, and Evolution -- the first comprehensive reference on current knowledge of diverse species that exhibit unique survival strategies and provide important models for basic and applied research. This work fills a void, covering the life cycle, reproductive biology, evolutionary ecology, reproductive behavior, sexual selection, genetics, speciation, and integrative and conservation strategies of annual fishes. Bringing together researchers in different areas of annual fishes to summarize previous work, overview the current research, and highlight promising areas of research, the book is organized into three sections focusing on: Diversity, life history, and reproductive biology Ecology and conservation Evolution The book provides a thorough understanding of the complexity of annual fishes and emphasizes their usefulness as a unique model organism for studies in vertebrate biology, particularly in areas such as speciation and senescence. It also notes the gaps in knowledge that challenge future research and encourages the continued expansion and development of research studies on annual fishes to address these gaps so that general vertebrate biology can be better understood. It serves as a valuable resource for scientists in a range of disciplines such as ichthyology, zoology, developmental and evolutionary biology, molecular biology and genetics, and ecology. Close

• 3. [Article] Temporary Environments

  This is a book chapter within Extremophile Fishes. This book summarizes the key adaptations enabling extremophile fishes to survive under harsh environmental conditions. It reviews the most recent research ...

  Citation × Citation Citation Abstract Copy Title: Temporary Environments Author: Polacik, Matej, Podrabsky, Jason E. Year: 2015 This is a book chapter within Extremophile Fishes. This book summarizes the key adaptations enabling extremophile fishes to survive under harsh environmental conditions. It reviews the most recent research on acidic, Antarctic, cave, desert, hypersaline, hypoxic, temporary, and fast-flowing habitats, as well as naturally and anthropogenically toxic waters, while pointing out generalities that are evident across different study systems. Knowledge of the different adaptations that allow fish to cope with stressful environmental conditions furthers our understanding of basic physiological, ecological, and evolutionary principles. In several cases, evidence is provided for how the adaptation to extreme environments promotes the emergence of new species. Furthermore, a link is made to conservation biology, and how human activities have exacerbated existing extreme environments and created new ones. The book concludes with a discussion of major open questions in our understanding of the ecology and evolution of life in extreme environments. Title: Temporary Environments Author: Polacik, Matej, Podrabsky, Jason E. Year: 2015 This is a book chapter within Extremophile Fishes. This book summarizes the key adaptations enabling extremophile fishes to survive under harsh environmental conditions. It reviews the most recent research on acidic, Antarctic, cave, desert, hypersaline, hypoxic, temporary, and fast-flowing habitats, as well as naturally and anthropogenically toxic waters, while pointing out generalities that are evident across different study systems. Knowledge of the different adaptations that allow fish to cope with stressful environmental conditions furthers our understanding of basic physiological, ecological, and evolutionary principles. In several cases, evidence is provided for how the adaptation to extreme environments promotes the emergence of new species. Furthermore, a link is made to conservation biology, and how human activities have exacerbated existing extreme environments and created new ones. The book concludes with a discussion of major open questions in our understanding of the ecology and evolution of life in extreme environments. Close

• 4. [Article] Desert Environments

  This is a book chapter within Extremophile Fishes. This book summarizes the key adaptations enabling extremophile fishes to survive under harsh environmental conditions. It reviews the most recent research ...

  Citation × Citation Citation Abstract Copy Title: Desert Environments Author: Hillyard, Stanley D., Podrabsky, Jason E., van Breukelen, Frank Year: 2015 This is a book chapter within Extremophile Fishes. This book summarizes the key adaptations enabling extremophile fishes to survive under harsh environmental conditions. It reviews the most recent research on acidic, Antarctic, cave, desert, hypersaline, hypoxic, temporary, and fast-flowing habitats, as well as naturally and anthropogenically toxic waters, while pointing out generalities that are evident across different study systems. Knowledge of the different adaptations that allow fish to cope with stressful environmental conditions furthers our understanding of basic physiological, ecological, and evolutionary principles. In several cases, evidence is provided for how the adaptation to extreme environments promotes the emergence of new species. Furthermore, a link is made to conservation biology, and how human activities have exacerbated existing extreme environments and created new ones. The book concludes with a discussion of major open questions in our understanding of the ecology and evolution of life in extreme environments. Title: Desert Environments Author: Hillyard, Stanley D., Podrabsky, Jason E., van Breukelen, Frank Year: 2015 This is a book chapter within Extremophile Fishes. This book summarizes the key adaptations enabling extremophile fishes to survive under harsh environmental conditions. It reviews the most recent research on acidic, Antarctic, cave, desert, hypersaline, hypoxic, temporary, and fast-flowing habitats, as well as naturally and anthropogenically toxic waters, while pointing out generalities that are evident across different study systems. Knowledge of the different adaptations that allow fish to cope with stressful environmental conditions furthers our understanding of basic physiological, ecological, and evolutionary principles. In several cases, evidence is provided for how the adaptation to extreme environments promotes the emergence of new species. Furthermore, a link is made to conservation biology, and how human activities have exacerbated existing extreme environments and created new ones. The book concludes with a discussion of major open questions in our understanding of the ecology and evolution of life in extreme environments. Close

• 5. [Article] Mechanisms of Animal Diapause: Recent Developments from Nematodes, Crustaceans, Insects, and Fish

  Life cycle delays are beneficial for opportunistic species encountering suboptimal environments. Many animals display a programmed arrest of development (diapause) at some stage(s) of their development, ...

  Citation × Citation Citation Abstract Copy Title: Mechanisms of Animal Diapause: Recent Developments from Nematodes, Crustaceans, Insects, and Fish Author: Hand, Steven C., Denlinger, David L., Podrabsky, Jason E., Roy, Richard Year: 2016 Life cycle delays are beneficial for opportunistic species encountering suboptimal environments. Many animals display a programmed arrest of development (diapause) at some stage(s) of their development, and the diapause state may or may not be associated with some degree of metabolic depression. In this review, we will evaluate current advancements in our understanding of the mechanisms responsible for the remarkable phenotype, as well as environmental cues that signal entry and termination of the state. The developmental stage at which diapause occurs dictates and constrains the mechanisms governing diapause. Considerable progress has been made in clarifying proximal mechanisms of metabolic arrest and the signaling pathways like insulin/Foxo that control gene expression patterns. Overlapping themes are also seen in mechanisms that control cell cycle arrest. Evidence is emerging for epigenetic contributions to diapause regulation via small RNAs in nematodes, crustaceans, insects, and fish. Knockdown of circadian clock genes in selected insect species supports the importance of clock genes in the photoperiodic response that cues diapause. A large suite of chaperone-like proteins, expressed during diapause, protects biological structures during long periods of energy-limited stasis. More information is needed to paint a complete picture of how environmental cues are coupled to the signal transduction that initiates the complex diapause phenotype, as well as molecular explanations for how the state is terminated. Excellent examples of molecular memory in post-dauer animals have been documented in Caenorhabditis elegans It is clear that a single suite of mechanisms does not regulate diapause across all species and developmental stages. Title: Mechanisms of Animal Diapause: Recent Developments from Nematodes, Crustaceans, Insects, and Fish Author: Hand, Steven C., Denlinger, David L., Podrabsky, Jason E., Roy, Richard Year: 2016 Life cycle delays are beneficial for opportunistic species encountering suboptimal environments. Many animals display a programmed arrest of development (diapause) at some stage(s) of their development, and the diapause state may or may not be associated with some degree of metabolic depression. In this review, we will evaluate current advancements in our understanding of the mechanisms responsible for the remarkable phenotype, as well as environmental cues that signal entry and termination of the state. The developmental stage at which diapause occurs dictates and constrains the mechanisms governing diapause. Considerable progress has been made in clarifying proximal mechanisms of metabolic arrest and the signaling pathways like insulin/Foxo that control gene expression patterns. Overlapping themes are also seen in mechanisms that control cell cycle arrest. Evidence is emerging for epigenetic contributions to diapause regulation via small RNAs in nematodes, crustaceans, insects, and fish. Knockdown of circadian clock genes in selected insect species supports the importance of clock genes in the photoperiodic response that cues diapause. A large suite of chaperone-like proteins, expressed during diapause, protects biological structures during long periods of energy-limited stasis. More information is needed to paint a complete picture of how environmental cues are coupled to the signal transduction that initiates the complex diapause phenotype, as well as molecular explanations for how the state is terminated. Excellent examples of molecular memory in post-dauer animals have been documented in Caenorhabditis elegans It is clear that a single suite of mechanisms does not regulate diapause across all species and developmental stages. Close

• 6. [Article] Hypoxia and Anoxia Tolerance in the Annual Killifish Austrofundulus Limnaeus

  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 ...

  Citation × Citation Citation Abstract Copy Title: Hypoxia and Anoxia Tolerance in the Annual Killifish Austrofundulus Limnaeus Author: Podrabsky, Jason E., Wilson, Natalie E. Year: 2016 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. Title: Hypoxia and Anoxia Tolerance in the Annual Killifish Austrofundulus Limnaeus Author: Podrabsky, Jason E., Wilson, Natalie E. Year: 2016 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. Close

• 7. [Article] Embryonic Development of the Annual Killifish Austrofundulus limnaeus: An Emerging Model for Ecological and Evolutionary Developmental Biology Research and Instruction

  Background: Austrofundulus limnaeus is an annual killifish from the Maracaibo basin of Venezuela. Annual killifishes are unique among vertebrates in their ability to enter into a state of dormancy at up ...

  Citation × Citation Citation Abstract Copy Title: Embryonic Development of the Annual Killifish Austrofundulus limnaeus: An Emerging Model for Ecological and Evolutionary Developmental Biology Research and Instruction Author: Podrabsky, Jason E., Riggs, Claire L., Romney, Amie L., Woll, S. Cody, Wagner, Josiah T., Culpepper, Kristin M., Cleaver, Timothy Grant Year: 2017 Background: Austrofundulus limnaeus is an annual killifish from the Maracaibo basin of Venezuela. Annual killifishes are unique among vertebrates in their ability to enter into a state of dormancy at up to three distinct developmental stages termed diapause I, II, and III. These embryos are tolerant of a wide variety of environmental stresses and develop relatively slowly compared with nonannual fishes. Results: These traits make them an excellent model for research on interactions between the genome and the environment during development, and an excellent choice for developmental biology laboratories. Furthermore, A. limnaeus is relatively easy to maintain in a laboratory setting and has a high fecundity, making it an excellent candidate as an emerging model for studies of development, and for defining the limits of developmental buffering in vertebrates. Conclusions: This study reports for the first time on the detailed development of A. limnaeus and provides a photographic and illustrated atlas of embryos on the two developmental trajectories possible in this species. Title: Embryonic Development of the Annual Killifish Austrofundulus limnaeus: An Emerging Model for Ecological and Evolutionary Developmental Biology Research and Instruction Author: Podrabsky, Jason E., Riggs, Claire L., Romney, Amie L., Woll, S. Cody, Wagner, Josiah T., Culpepper, Kristin M., Cleaver, Timothy Grant Year: 2017 Background: Austrofundulus limnaeus is an annual killifish from the Maracaibo basin of Venezuela. Annual killifishes are unique among vertebrates in their ability to enter into a state of dormancy at up to three distinct developmental stages termed diapause I, II, and III. These embryos are tolerant of a wide variety of environmental stresses and develop relatively slowly compared with nonannual fishes. Results: These traits make them an excellent model for research on interactions between the genome and the environment during development, and an excellent choice for developmental biology laboratories. Furthermore, A. limnaeus is relatively easy to maintain in a laboratory setting and has a high fecundity, making it an excellent candidate as an emerging model for studies of development, and for defining the limits of developmental buffering in vertebrates. Conclusions: This study reports for the first time on the detailed development of A. limnaeus and provides a photographic and illustrated atlas of embryos on the two developmental trajectories possible in this species. Close

• 8. [Article] Mitochondrial DNA Sequence and Lack of Response to Anoxia in the Annual Killifish <i>Austrofundulus limnaeus</i>

  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 ...

  Citation × Citation Citation Abstract Copy Title: Mitochondrial DNA Sequence and Lack of Response to Anoxia in the Annual Killifish <i>Austrofundulus limnaeus</i> Author: Wagner, Josiah T., Chavez, Florisela H., Podrabsky, Jason E. Year: 2016 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. Title: Mitochondrial DNA Sequence and Lack of Response to Anoxia in the Annual Killifish <i>Austrofundulus limnaeus</i> Author: Wagner, Josiah T., Chavez, Florisela H., Podrabsky, Jason E. Year: 2016 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. Close

• 9. [Article] Gene Expression Patterns That Support Novel Developmental Stress Buffering in Embryos of the Annual Killifish <i>Austrofundulus limnaeus</i>

  Background: The cellular signaling mechanisms and morphogenic movements involved in axis formation and gastrulation are well conserved between vertebrates. In nearly all described fish, gastrulation and ...

  Citation × Citation Citation Abstract Copy Title: Gene Expression Patterns That Support Novel Developmental Stress Buffering in Embryos of the Annual Killifish <i>Austrofundulus limnaeus</i> Author: Wagner, Josiah T., Podrabsky, Jason E. Year: 2015 Background: The cellular signaling mechanisms and morphogenic movements involved in axis formation and gastrulation are well conserved between vertebrates. In nearly all described fish, gastrulation and the initial patterning of the embryonic axis occur concurrently with epiboly. However, annual killifish may be an exception to this norm. Annual killifish inhabit ephemeral ponds in South America and Africa and permanent populations persist by the production of stress-tolerant eggs. Early development of annual killifish is unique among vertebrates because their embryonic blastomeres disperse randomly across the yolk during epiboly and reaggregate several days later to form the embryo proper. In addition, annual killifish are able to arrest embryonic development in one to three stages, known as diapause I, II, and III. Little is known about how the highly conserved developmental signaling mechanisms associated with early vertebrate development may have shifted in order to promote the annual killifish phenotype. One of the most well-characterized and conserved transcription factors, oct4 (Pou5f1), may have a role in maintaining pluripotency. In contrast, BMP-antagonists such as chordin, noggin, and follistatin, have been previously shown to establish dorsal-ventral asymmetry during axis formation. Transcription factors from the SOXB1 group, such as sox2 and sox3, likely work to induce neural specification. Here, we determine the temporal expression of these developmental factors during embryonic development in the annual killifish Austrofundulus limnaeus using quantitative PCR and compare these patterns to other vertebrates. Results: Partial transcript sequences to oct4, sox2, sox3, chordin, noggin-1, noggin-2, and follistatin were cloned, sequenced, and identified in A. limnaeus. We found oct4, sox3, chordin, and noggin-1 transcripts to likely be maternally inherited. Expression of sox2, follistatin, and noggin-2 transcripts were highest in stages following a visible embryonic axis. Conclusions: Our data suggest that embryonic cells acquire their germ layer identity following embryonic blastomere reaggregation in A. limnaeus. This process of cellular differentiation and axis formation may involve similar conserved signaling mechanisms to other vertebrates. We propose that the undifferentiated state is prolonged during blastomere dispersal, thus functioning as a developmental stress buffer prior to the establishment of embryonic asymmetry and positional identity among the embryonic cells. Title: Gene Expression Patterns That Support Novel Developmental Stress Buffering in Embryos of the Annual Killifish <i>Austrofundulus limnaeus</i> Author: Wagner, Josiah T., Podrabsky, Jason E. Year: 2015 Background: The cellular signaling mechanisms and morphogenic movements involved in axis formation and gastrulation are well conserved between vertebrates. In nearly all described fish, gastrulation and the initial patterning of the embryonic axis occur concurrently with epiboly. However, annual killifish may be an exception to this norm. Annual killifish inhabit ephemeral ponds in South America and Africa and permanent populations persist by the production of stress-tolerant eggs. Early development of annual killifish is unique among vertebrates because their embryonic blastomeres disperse randomly across the yolk during epiboly and reaggregate several days later to form the embryo proper. In addition, annual killifish are able to arrest embryonic development in one to three stages, known as diapause I, II, and III. Little is known about how the highly conserved developmental signaling mechanisms associated with early vertebrate development may have shifted in order to promote the annual killifish phenotype. One of the most well-characterized and conserved transcription factors, oct4 (Pou5f1), may have a role in maintaining pluripotency. In contrast, BMP-antagonists such as chordin, noggin, and follistatin, have been previously shown to establish dorsal-ventral asymmetry during axis formation. Transcription factors from the SOXB1 group, such as sox2 and sox3, likely work to induce neural specification. Here, we determine the temporal expression of these developmental factors during embryonic development in the annual killifish Austrofundulus limnaeus using quantitative PCR and compare these patterns to other vertebrates. Results: Partial transcript sequences to oct4, sox2, sox3, chordin, noggin-1, noggin-2, and follistatin were cloned, sequenced, and identified in A. limnaeus. We found oct4, sox3, chordin, and noggin-1 transcripts to likely be maternally inherited. Expression of sox2, follistatin, and noggin-2 transcripts were highest in stages following a visible embryonic axis. Conclusions: Our data suggest that embryonic cells acquire their germ layer identity following embryonic blastomere reaggregation in A. limnaeus. This process of cellular differentiation and axis formation may involve similar conserved signaling mechanisms to other vertebrates. We propose that the undifferentiated state is prolonged during blastomere dispersal, thus functioning as a developmental stress buffer prior to the establishment of embryonic asymmetry and positional identity among the embryonic cells. Close