Since you visited this site, you will probably also be interested in Developmental Physiology, a research community based Web site for developmental physiologists world-wide.

We are interested in understanding how some animals survive environmental stresses that would otherwise be detrimental to humans. We are currently using two systems to study the metazoan response to environmental changes the nematode C. elegans and the zebrafish Danio rerio. We are particularly interested in how oxygen deprivation effects cell cycle progression, developmental regulation, and the molecular mechanisms controling oxygen deprivation responses and survival.

THE WONDERFUL WORM:

C. elegans is an excellent and popular model system to understand development. C. elegans is a small soil nematode with a short life cycle. The worm can be either a male or a hermaphrodite, thus allowing reproduction by self-fertilization or cross-fertilization. Dispite the "simplicity" of the worm many different cell types and tissues are present. The genome is completely sequenced and the ability to do forward genetics, RNA interference and reverse genetics makes this an excellent biological model system. Besides all of these great attributes... worms are just plain fun to watch and study!! Also the fact that worms are a genetic model system that is able to survive a variety of stresses including oxygen deprivation allows us to answer biological quesions at the molecular, genetic and cellular level.

THE FACINATING ZEBRAFISH:

Danio rerio is used by researchers throughout the world to understand vertebrate development. The advantages for using zebrafish are fast development time, transparent embryo, genetics, small size, and the ability to obtain a large amount of embryos. We were interested in studying the developmental response zebrafish have to oxygen deprivation because of the well documented embryonic stages and the transparency of the embryo. Furthermore comparative studies with this model system and C. elegans may allow us to understand oxygen deprivation mechanisms in consideration of adaptation and evolution. Zebrafish are incredible to watch develop and are a popular system for scientific research and K-12 science education.

Oxygen Deprivation:

Oxygen deprivation is a critical factor in several medical problems including myocardial infarction, pulmonary disease and dysfunction, anemia, blood loss, suffocation, sleep apnea, stroke, and resistance of solid tumor cells to radiation and chemotherapy. The detrimental effects of oceanic “dead zone” regions, in which oxygen levels are reduced or depleted due to natural and/or human activities, are another concern. Thus, health and environmental issues associated with oxygen deprivation are economically relevant challenges (billions of U.S. dollars are spent on this problem). Animal model systems are used to understand the molecular and physiological response that organisms, tissues, and cells have to oxygen deprivation. Yet, to date, oxygen-deprivation protective or tissue repair mechanisms are not completely understood.

Zebrafish Embryos:

We have found that young zebrafish embryos survive anoxia (0% O₂) by entering into a reversible state of suspended animation. That is cell division is arrested and all observable movement such as heartbeat and development ceases until oxygen is reintroduced into the environment. Analysis of cell-cycle changes in blastomeres exposed to anoxia, we found that no cells arrested in mitosis. Flow cytometry analysis revealed that blastomeres arrest during S and G2 phases of the cell cycle. We are interested in understanding the mechanisms that control cessation of many biological events in response to oxygen deprivation. In particular we are interested in how anoxia signals the blastomeres to arrest at specific stages of the cell cycle. See this publication for more detail.

Caenorhabditis elegans:

The nematode C. elegans is an excellent genetic and developmental model system. We believe that worms are an excellent system to study oxygen deprivation. Nematodes exposed to anoxia enter into a state of suspended animation in that all cell division, developmental progression, feeding and motility cease. We are using forward and reverse genetic (RNAi) as well as cell biological techniques to understand this interesting yet poorly understood phenomenon of anoxia-induced suspended animation.


Nematodes arrest development in response to anoxia. Botom panel are worms exposed to anoxia. See this publication for more detail.		Oxygen deprivation influences the developmental growth of organisms.

Cell Cycle and Anoxia:

We are interested in developing cell biological markers to study cell cycle arrest in developing nematode and zebrafish embryos exposed to anoxia. Previous work using cell biological techniques indicate that nematode embryos exposed to anoxia arrest during interphase and all stages of mitosis except anaphase. We are interested in indentifying gene products that are required for anoxia induced cell cycle arrest. We are using geneic techiques to identify such genes.

Anoxia and Metabolism:

In C. elegans the DAF-2/DAF-16 pathway, an IGF-1/insulin-like signaling pathway, is involved with dauer formation, longevity and stress resistance. In this report we compared the response wild-type and daf-2(e1370) animals have to anoxia. Unlike wild-type animals, the daf-2(e1370) animals have an enhanced anoxia-survival phenotype in that they survive long-term anoxia and high-temperature anoxia, do not accumulate significant tissue damage in either of these conditions and are motile after 24 hrs of anoxia. RNA interference was used to screen DAF-16 regulated genes that suppress the daf-2(e1370) enhanced anoxia-survival phenotype. We identified gpd-2 and gpd-3; two nearly identical genes in an operon that encode the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase. We found that not only is the daf-2(e1370) enhanced anoxia phenotype dependent upon gpd-2/3 but the motility of animals exposed to brief periods of anoxia is prematurely arrested in gpd-2/3(RNAi) and daf-2(e1370);gpd-2/3(RNAi) animals. These data suggest that gpd-2/3 may serve a protective role in tissue exposed to oxygen deprivation.

Starvation:

Microorganisms such as yeast can withstand long periods of nutrient deprivation, however metazoans are less adapted to such a stress. The nematode C. elegans has adapted the ability to enter into a dauer larval stage in response to environmental signals such as starvation, pheromone, and high temperatures. The genes that are important for this interesting life cycle stage are well studied. Additionally, young larvae (L1) are also able to survive periods of starvation. We are interested in studying the mechanisms that are required for starvation survival and understanding general versus specific stress responses in the nematode.

Significance:

Organisms are exposed to environmental stresses during its life cycle.

Oxygen deprivation is central to the pathology of diseases including cardiac and pulmonary dysfunction. Cancerous cells within solid tumors are often deprived of oxygen and these oxygen deprived cancerous cells are known to be more resistant to radiation and chemotherapy. In spite of the widely appreciated topic of oxygen deprivation, there are critical gaps in the knowledge base.

Starvation is a stress that organisms often encounter in nature and many humans on earth are deprived of the basic nutrients for proper growth and development. Nutrient deprivation also occurs in isolated tissues as a result of a decrease of blood flow. Understanding the molecular mechanisms that enables an organism to survive such a stress will aid in our understanding of conditions such as ischemia.

It is our hope that studying stress responses such as oxygen deprivation and nutrient starvation will not only lead to a greater understanding of developmental processes but also lead to health benefits for humans.

Current Research Projects:

Systematic RNA interference screen to identify genes required for embryos to survive anoxia
Reverse genetic and classical forward genetics to identify genes required for embryos to survive oxygen deprivation
Production of markers to understand anoxia-induced suspended animation
Physiology of nematodes exposed to long term oxygen deprivation
Molecular evolution of responses to oxygen deprivation

Interested..... email Pam Padilla at ppadilla@unt.edu

Research Supported by National Institutes of Health

Movies of Interest

Supplemental Figure MCB

Last Modified: 05 December 2002