UNDERSTANDING THE MOLECULAR BASIS FOR CHROMOSOME ANEUPLOIDY USING ZEBRAFISH AS A MODEL GENETIC VERTEBRATE SPECIES

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 1004943
• Project Start Date: Oct 31, 2014
• Project End Date: Aug 10, 2017
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF CALIFORNIA, DAVIS
410 MRAK HALL
DAVIS,CA 95616-8671

Performing Department
Molecular and Cellular Biology

Non Technical Summary
Both animal husbandry and crop breeding depend on reproductive health of organisms. One key feature of gametogenesis is the proper pairing and segregation of chromosomes to form sperm and eggs, gametophytes or spores in animals, plants and fungi, respectively. Errors in molecular events underlying chromosome segregation can lead to infertility or an increase in spontaneous abortions in plants and animals by increasing the incidence of aneuploidy, which is having the wrong numbers of chromosomes. Compounds found in the environment such as chemical fertilizers, food storage containers and industrial waste and even climate change can increase the risk of aneuploidy. By contrast, induction of aneuploidy or genome duplication in plants can be an important driver of new traits without the need to create transgenic products. Our research is to identify and understand the roles of the underlying protein targets of these genotoxic agents at a molecular level. The outcome of this research will help us to better limit the risks and economic losses associated with birth defects and spontaneous abortion in animals and to enhance breeding of crop plants.

Animal Health Component

(N/A)

Research Effort Categories

Basic

100%

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
723	7010	1080	40%
304	3840	1050	40%
201	2499	1081	20%

Knowledge Area
201 - Plant Genome, Genetics, and Genetic Mechanisms; 723 - Hazards to Human Health and Safety; 304 - Animal Genome;

Subject Of Investigation
3840 - Laboratory animals; 7010 - Biological Cell Systems; 2499 - Plant research, general;

Field Of Science
1081 - Breeding; 1080 - Genetics; 1050 - Developmental biology;

Keywords

chromosomes

cells

environment

aneuploidy

gametogenesis

birth defects

climate change

Goals / Objectives
Both animal husbandry and crop breeding depend on reproductive health of organisms. One key feature of gametogenesis is the proper pairing and segregation of chromosomes to form sperm and eggs, gametophytes or spores in animals, plants and fungi, respectively. Errors in molecular events underlying chromosome segregation can lead to infertility or an increase in spontaneous abortions in plants and animals by increasing the incidence of aneuploidy, the cellular condition of having too many or too few chromosomes. Our overarching goal is to understand the molecular and cellular processes that promote reproductive resilience. Zebrafish, Danio rerio, is an excellent model to assess the chromosome basis for embryonic lethality because they produce hundreds of progeny throughout their lives, embryonic development occurs outside the body and site-specific mutations that disrupt key molecular events of meiosis can be easily generated in the lab. Zebrafish is also an ideal model vertebrate organism to use for the development of bioassays to quantitatively measuring reproductive resilience due to their ease of growth in the lab, their similarities in terms of genome organization and embryology, the importance of fish in the human diet and as a sentinel organism that is acutely sensitive to waterborne pollutants and climate change. The specific objectives of our research are to 1)Determine the frequency of chromosome aneuploidy in males versus female zebrafish; 2) test if mutations that disrupt meiotic chromosome architecture differentially sensitize males versus females for chromosome segregation errors; and 3) to determine if known genotoxic agents differentially affect males versus female gametogenesis.

Project Methods
The following methods will be used to acheive the objectives of the project.1. Determine the frequency of chromosome aneuploidies staged-malformed embryos Methods: The rate of chromosome missegregation in zebrafish is unknown, yet testable. Since zebrafish embryos develop outside the body, the developmental profiles of hundreds of embryos can be easily assessed using a dissection microscope. Representative embryos arrested at various stages of development will be processed to assess the copy number of each chromosome. There are various ways to do this from the most laborious, karyotype analysis of metaphase-arrested cells, to high-throughput digital PCR analysis. Minimally, individual malformed embryos will be placed in wells of a 96-well micro-titer plate. Multiplex PCR using chromosome-specific primers will be carried out on DNA isolated from individual embryos. Sufficient numbers of embryos will be analyzed to test the confidence limits for assigning specific chromosome aneuploidies with specific developmental defects. Chi-squared analysis can be used to assess deviation from a random distribution of events.Potential outcomes and interpretation: Our expectation is that malformed embryos are more likely to be aneuploid compared to normal embryos. Karyotype analysis can distinguish whether chromosome missegregation arose during the formation of one of the parent gametes (i.e. all cells have aberrant karyotypes) versus aneuploidy generated after the first embryonic divisions (i.e. embryos are mosaic for cells with normal abnormal karyotypes). As is the case for humans, we expect that different chromosome aneuploidies will cause arrest at different developmental stages. For example, trisomy 21 is the only non-sex chromosome trisomy that develops to puberty.2. Test if mutations that disrupt meiotic chromosome architecture differentially sensitize males versus females for chromosome segregation errors.Rationale: Mutations that compromise meiotic chromosome architecture are expected to sensitize strains to generate increased levels of aneuploid gametes. Rad21 and Rad21L1 are cohesin proteins required for maintaining the loop-axis chromosome arrangement. Rad21 functions in somatic cells. Evidence in mouse suggests that Rad21L1 orthologs mediate homologous chromosome pairing. We have created a zebrafish line that generates rad21L1 homozygotes for analysis of the chromosome stages of meiosis.Methods: Embryo viability from fertilization to hatching will be measured in wild type, rad21, and rad21L1 strains. Embryos will be generated from pairwise crosses involving mutant males or mutant females crossed to wild type animals of the opposite sex. If we find that fecundity, but not embryonic viability, is reduced in females then we will test if gametocytes have undergone increased levels of apoptosis to assess if oogenesis progressed past late stages of meiotic prophase. We can also allow cells to bypass apoptosis by deleting the p53 gene. In this background, meiosis will be completed and we can directly assess the chromosome defects that would otherwise lead to arrest. For males, sperm concentration in their milt and sperm motility will be measured. We will measure rates of chromosome missegregation among terminally staged embryos by the most appropriate method established in Aim 1. WePotential outcomes and interpretation: An increased incidence of embryonic lethality caused by one or more of the cohesin mutants would indicate that the corresponding wild type cohesin is required for producing a gamete that supports life. Embryonic lethality may be manifested in different ways. 1) The frequency of inviable embryos might be increased only when either the male or the female parent carries the cohesin mutation. This outcome would suggest the success of either oogenesis or spermatogenesis depends on sex-specific chromosome architecture. 2) Brood size may be reduced without a corresponding change in the frequency of inviable progeny. This could arise if a population of aberrant gametes is eliminated by apoptosis or by their inability to engage in fertilization. 3) The cohesin mutations may have no effect on the outcomes of meiosis. This result may be due to redundant functions of Rad21 and Rad21L proteins. If this is the case then double mutant strains will be created and analyzed similarly. If oogenesis is differentially affected by mutations in either or both rad21 and rad21L1 genes, this could give mechanistic insight into the molecular basis for the maternal age effect in humans where the incidence of infertility and trisomy is dramatically increased in women between the ages of 36 and 45. Analysis of rad21L1 p53 double mutants will be important to bypass the female specific arrest. Our expectation is that the addition of this mutation will increase the incidence in the formation of aneuploidy embryos, or even increase the rate of germ line tumor formation.3. Determine if genotoxic agents differentially affect males versus female gametogenesis.Rationale: Because zebrafish are cultured in water tanks, they make an excellent model for testing the mechanistic effects of drugs, given appropriate molecular assays. Our drinking water supply is contaminated with heavily prescribed pharmaceuticals including anti-depressants, mood stabilizers, sex hormones, opioid, anti-anxiety and antibiotics. Bis-phenol A is a breakdown product of food containers including canned foods and sodas and has been shown to increase the incidence of aneuploidy in mouse.Methods: Adult fish will be exposed to the upper limits of these drugs found in drinking water. The frequency of defective embryogenesis and chromosome aneuploidy will be measured as described above.Outcomes and interpretation: We expect that a subset of these agents will increase rates of aneuploidy in embryos in genetically sensitized strains and perhaps also in non-sensitized strains. It will be interesting to find if there are sex-specific differences in the levels of sensitivity to drug exposure. Success of this aim will provide proof of principle that zebrafish can be used as a sentinel organism for developing high-throughput toxicity assays. Of particular interest will be to determine the molecular targets that sensitive to the agents. These data will provide preliminary results to seek funding to identify these targets. Outcomes of these studies will be of interest to the general population.Milestones of the project will be met through the publication of the completed research in open access peer-reviewed journals. Students completing the research will be competetive candidates for open jobs.

Progress 10/31/14 to 08/10/17

Outputs
Target Audience:I gave several research seminars related to the project. I was an invited speaker at the Meiosis Gordon Research Conference in New London New Hampshire. This is the most important international conference for my field of research. A large focus of research in this group is the study of mechanism of aneuploidy which is a fundamental process of reproductive health that impacts humans livestock and plants and fisheries. This work was also presented at the Genetics Society of America Annual Zebrafish meeting. Over the review period I gave invited research seminars in the US, including Indiana University, the National Institutes of Health, and the Stowers Institute in Kanas City MO; three institutions in Japan, including University of Tokyo, the Nara Institute of Science and Technology and Osaka University; seminar at Otago University in New Zealand where I did a six month sabbatical to learn about zebrafish model, and to undergraduate students at Xavier University of Louisiana and two Land Grant institutions that are also Historically Black Colleges and Universities, including the University of Maryland Eastern Shore and Florida A&M University. In June 2017 I presented a talk for a lay audience as part of the Science Cafe series in Davis CA. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?During the period of review I have trained two postdoctoral fellows, two graduate students, two technicians, one senior research associate and nine undergraduate students. This summer I hosted a student from Xavier University of Louisiana as part of the Molecular and Cell Biology Graduate Admissions Pathway under the University of California initiative to bring students from Historically Black Colleges and Universities to UC Davis for a summer research program, for which I am the lead PI. I am also the faculty mentor to a student in the NIH funded PREP program and he plans to apply to UC Davis in the fall and continue his research on this project. How have the results been disseminated to communities of interest?Hinjosa, Xiong 2016; Martinez, Chu 2015. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? The goals of the project were to 1) Determine the frequency of chromosome aneuploidy in male versus female zebrafish; 2) test if mutations that disrupt meiotic chromosome architecture differentially sensitize males versus females for chromosome segregation errors; and 3) to determine if known genotoxic agents differentially affect males versus female gametogenesis. For aim 1 we created a chromosome spread procedure to count the number of chromosomes in metaphase cells isolated from zebrafish embryos. As a first step, we compared chromosome numbers in embryos from mutant mothers with a deletion in the spo11 gene and from wild type mothers. Since spo11 fails to make DNA double-strand breaks, the initiating event of meiotic recombination, our expectation was that chromosome missegregation events would be greater in spo11 mothers. We found a dramatic and significant difference in chromosome number in embryos from the spo11-/- mothers. Moreover, embryos with the incorrect numbers of chromosomes show severe developmental defects. Interestingly, while the spo11-/- mothers were fertile, the males failed to make sperm entirely. We investigated the molecular basis for the sexually dimorphic phenotype and found that early chromosome events of meiosis, including telomere associations, clustering of telomeres in to the bouquet, and the formation of chromosome axes were similar in wild type and in spo11 males and females. In both male and female spo11 mutants, chromosomes failed to undergo synapsis and pair homologous chromosomes. We further characterized the male meiosis to find at which stage the development of spermatocytes arrested. By staining whole mount testis with antibodies to the germline marker, Vasa, and the DNA staining dye, DAPI, we found an increased population of cells in metaphase suggesting that in the absence of Spo11 spermatogenesis halts in metaphase I. These results show that the cause of cell cycle arrest in males is not present in females or, alternatively, a more stringent checkpoint operates in males that prevents the formation of aneuploid sperm. With a new R01 grant awarded to my lab from the NIH, we are continuing these studies to measure chromosome aneuploidy in defective embryos from crosses involving wild type males and females. Our preliminary studies show that these events are very rare, so collecting sufficient numbers of embryos with developmental delays has been challenging. With these new funds, we can train undergraduates to continue to set up matings to score progeny for developmental defects and aneuploidy. Aim 2) We next focused on meiotic defects in males and females carrying mutations in genes known to be involved in chromosome axis structure. To this end we created a deletion mutation in the meiosis-specific cohesin, rad21l1. Rad21L1 has been shown previously in mouse to be required for spermatogenesis. Surprisingly, in zebrafish, rad21l1 mutant males are fertile and give very few offspring with developmental abnormalities, similar to wild type. The dramatic difference in the rad21l1 mutant phenotype between mouse and zebrafish, along with the fact that zebrafish synapsis more resembles human males compared to mouse, suggests that mouse may not be a reliable model for human meiosis. Interestingly, rad21l1-/- homozygous females are absent among progeny from a cross between heterozygous males and females, i.e. rad21l1+/-. Further inspection reveals that oogenesis fails. In zebrafish, oogenesis is required for female development and the fish develop into males (zebrafish do not have sex chromosomes). Again, differences between the mouse and zebrafish phenotypes suggest that sexually dimorphic features of gametogenesis may not be conserved among vertebrates. Aim 3) Given the fact that different mutations have different affects in males versus females, we next explored if the failure to repair DNA double strand breaks resulted in different phenotypes in males and females. To test this, we obtained mutant fish with a mutation that disrupts the mnd1 gene. Surprisingly, mnd1-/- zebrafish males can be recovered from a heterozygous incross but not females. This is similar to what we observed for the rad21l1 phenotype. These results support two conclusions: first, mnd1-/- is not required for viability, and second, mnd1 appears to be required for female development, perhaps due to a defect in oogenesis. Analysis of intact testes showed that the fish could make sperm, yet fertilization was dramatically reduced. To test if the mnd1-/- fish are defective for repairing DSBs we stained whole-mount testis with the DSB marker gamma-H2AX. Preliminary results suggest that the fraction of meiotic cells with DSBs may be higher than in wild type, suggesting a defect in repair. We are currently testing if the sperm contain unrepaired DSBs and this is the cause of infertility. Our next step is to irradiate spo11 fish to create exogenous DSBs and assay if these breaks are repaired and if they can rescue the meiotic arrest in spo11 mutant males by visualizing the distribution of cells types (i.e. sperm) in the testis. Simultaneously, we will test if exogenous DSBs can rescue developmental delays in embryos from spo11 mothers by decreasing the level of aneuploidy. In contrast to the zebrafish mutant phenotypes, male mice that carry defective copies of mnd1 fail to repair DSBs and fail to make sperm or eggs. This difference again highlights differences between mouse and zebrafish. Because the steps leading to synapsis and pairing are more similar between zebrafish and humans, we propose that zebrafish may be a better model for human biology than mouse. Future directions: Our data indicate that zebrafish is an excellent model organism to explore the roles of chromosome dynamics in promoting proper chromosome segregation. In humans, chromosome missegregation in meiosis is the leading cause of birth defects and mental retardation in humans (e.g. trisomy 21 that leads to Down Syndrome. Recent analysis of transcriptomes in individual cells in the male testis in Bruce Draper's lab has revealed a list of previously unannotated genes that may play a role in meiosis. The ease of creating new mutations in zebrafish, the recovery of hundreds of progeny in a single cross, and the easily accessible and transparent gonads make zebrafish and excellent model for gene discovery and rapid analysis of mutant phenotypes.

Publications

• Type: Journal Articles Status: Published Year Published: 2017 Citation: Chu DB, Gromova, T, Newman, AC, and Burgess SM. The nucleoporin Nup2 contains a meiotic-autonomous region that promotes the dynamic chromosome events of meiosis. Genetics 206(3): 1319-1327.

Progress 10/01/15 to 09/30/16

Outputs
Target Audience:Our research focuses on the molecular mechanisms underlying reproductive health. The research carried out under the California Agricultural Experiment Station is greatly enhanced by close contact with animal and plant breeders at the UC Davis campus. Many of these researchers are members of the UC Davis Integrative Genetics and Genomics graduate group where I am the master academic advisor. In this role I have many chances to discuss our work with other AES members and learn about their students' progress. I have a clear pulse on both the basic science and Experiment station specialists. Over the review period I gave several research seminars that focus of the molecular mechanisms leading to aneuploidy and compromising reproductive health. I was an invited speaker at the Meiosis Gordon Research Conference in New London New Hampshire. This is the most important international conference for my field of research. A large focus of research in this group is the study of mechanism of aneuploidy which is a fundamental process of reproductive health that impacts humans livestock and plants and fisheries. This work was also presented at the Genetics Society of America Annual Zebrafish meeting. I gave eight invited research seminars this year. One at Indiana University on our work on the use of budding yeast as a sentinel model organism for studying mechanism involved in maintaining correct ploidy during sexual reproduction, one at the National Institutes of Health on the use of zebrafish as model genetic organism to study reproductive health and mechanisms that lead to aneuploidy. I gave three presentations to undergraduate students at Xavier University of Louisiana and two Land Grant institutions that are also Historically Black Colleges and Universities, including the University of Maryland Eastern Shore and Florida A&M University. I also presented our work at the National Institutes of Health and three institutions in Japan, including the University of Tokyo, the Nara Institute of Science and Technology and Osaka University. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Dr. Trent Newman published a paper on diet and impact on reproductive health in zebrafish on work he did as a graduate student in the lab of Julia Horsfield at the University of Otago in New Zealand. While he was in my lab I read drafts of the manuscript and mentored him through the submission and revision process. This paper was published this year in PLoS One. Trent also wrote the first draft of the pilot grant we submitted on the effects of Atrazine on reproductive health in zebrafish. In addition, I am the PI on a three-year grant awarded by the University of California Office of the President Graduate Admissions Pathways Initiative for students from Historically Black Colleges and Universities. I have established partnerships with the University of Maryland Eastern Shore, Florida A&M University and Xavier University of Louisiana. This program will bring 6 African American students for a 10-week summer research and enrichment program with the goal that they will apply for graduate study at the University of California. I traveled to each of these institutions for recruitment and will have one student work in my lab this summer. I also train four undergraduates in my lab who work on projects relevant to reproductive health and aneuploidy. How have the results been disseminated to communities of interest?Dr. Newman has attended several meetings to present his work including American Society of Cell Biology meeting in San Francisco and . My graduate Yana Blokina, a graduate student in my lab presented a poster at the Genetics Society of America Zebrafish meeting in July 2016 in Orlando FL where I also gave a poster on the use of zebrafish as a new model organism to study sexually dimorphic features of germ cell formation in this species. What do you plan to do during the next reporting period to accomplish the goals?We plan to initiate experiments to study the effects of Atrazine on the reproductive health on reproduction in zebrafish. Atrazine is a potent endocrine disrupter and interferes with hormonal activity of animals and humans at extremely low doses. I will actively seek opportunities to for outreach at the K-12 and community level.

Impacts
What was accomplished under these goals? We have submitted a grant to the UC Davis Core Center for Environmental Health Sciences Pilot Projects Program entitled Epigenetic changes in the germline following exposure to the pesticide atrazine. The pesticide atrazine is a common environmental contaminant capable of impairing reproductive processes. This proposal will determine the mechanism of atrazine toxicity by analyzing gametogenesis in the zebrafish. Zebrafish are a useful model for toxicology studies due to the ease delivering toxicants via the water and the large numbers of externally developing offspring that they produce. Our work focuses on the reproductive consequences of atrazine exposure with changes in cellular metabolism. The metabolic pathways that are altered following atrazine exposure will inform us about the cellular processes affected by this toxicant. We will also analyze the impact of atrazine exposure on the conformation of the DNA in the germline by detecting covalent modifications made to the DNA. It is possible that epigenetic changes in the germline could mediate generational consequences of pesticide exposure. To gain insight into how the aberrant cellular processes develop during gametogenesis we will develop an innovative ex vivo gonad culture system that will allow cell of interest to be studied at specific stages. This system will also allow us to minimize exposure of live animals to the pesticide and could improve our understanding of the role of the endocrine system in pesticide toxicity. The integration of this novel approach to reproductive toxicity with new molecular technologies will allow for improved understanding normal and abnormal gametogenesis and inheritance. The tools built in this proposal and the knowledge gained from the results could on day help to shape environmental policy and improve the health and safety of local communities.

Publications

• Type: Journal Articles Status: Published Year Published: 2016 Citation: Chu DB, Burgess SM. A Computational Approach to Estimating Nondisjunction Frequency in Saccharomyces cerevisiae. G3 (Bethesda). 2016 Jan 8. pii: g3.115.024380.
• Type: Journal Articles Status: Published Year Published: 2015 Citation: Schuster K, Leeke B, Meier M, Wang Y, Newman T, Burgess S, Horsfield JA. A neural crest origin for cohesinopathy heart defects. Hum Mol Genet. 2015 Dec 15;24(24):7005-16.
• Type: Journal Articles Status: Published Year Published: 2016 Citation: Newman and Horsfield JA. Dietary intake influences adult fertility and offspring fitness in zebrafish. PLoS One 2016 11(11) e01663941(11).

Progress 10/31/14 to 09/30/15

Outputs
Target Audience: Our research focuses on the molecular mechanisms underlying reproductive health. The research carried out under the California Agricultural Experiment Station is greatly enhanced by close contact with animal and plant breeders at the UC Davis campus. Many of these researchers are members of the UC Davis Integrative Genetics and Genomics graduate group where I am the master academic advisor. In this role I have many chances to discuss our work with other AES members and learn about their students' progress. I have a clear pulse on both the basic science and Experiment station specialists. I also regularly participate in high school outreach by helping to conceive and write lesson plans, serving on various career panels when requested and mentoring high school students in my lab. UC Davis is surrounded by a rich agricultural industry in which these students' families are economically invested. Thus my outreach to K-12 students opens their eyes to opportunities to enter college-level STEM programs. During my sabbatical I served as a visiting professor at the University of Otago, Department of Pathology, Dunedin New Zealand from 01/01/2015-6/29/2015. Here I established an important collaboration with a Dr. Julia Horsfield to study the role of cohesin proteins in meiosis in zebrafish. I made many important contacts in New Zealand to help move our research forward. I recruited two New Zealand postdocs who are now currently working in my lab at UC Davis. In 2015 I gave research talks at several institutions including the Stowers Institute in Kansas City MO, University of California Davis, Nara Institute of Science and Technology in Japan, the University of Otago in Dunedin New Zealand and the University of Indiana. My student Yana Blokina presented her work at the EMBO conference at St. Catherine's College in Oxford England and the Northern California Zebrafish meeting at UCSF. I have sponsored under-represented minority students who have presented their work at UC Davis, and the Annual Biomedical Research Conference for Minority Students in Seattle, WA and the Biophysical Society Annual Meeting in San Francisco, CA. Changes/Problems:There have been no changes other than branching out to include as a vertebrate model. This work is funded by a supplement to my current NIH R01 grant. What opportunities for training and professional development has the project provided?Yana Blokhina is a Ph.D. candidate in the Integrative Genetics and Genomics graduate group at UC Davis. She has been working full time on studying chromosome aneuploidy rate in male versus female zebrafish. Her estimated graduation date is June 2017. Hester Roberts and Trent Newman are two postdocs recruited to work on the projects. Hester has been analyzing meiotic chromosome architecture and Trent is developing tools to study the real-time chromosome events of meiosis in cultured cells. Over the past year there have been four undergraduate students working on the project. The undergraduates are trained by Yana and the post-docs. There has also been on rotation student who carried out a bioinformatics approach to discovering the sites initiating homologous recombination in zebrafish males and females. How have the results been disseminated to communities of interest?I or my students have presented our findings at several national and international meetings as listed above. What do you plan to do during the next reporting period to accomplish the goals?I will present our findings to the Gordon Research Conference on Meiosis in New London New Hampshire in June 2016 and at the Genetics Society of America conference in Orlando Florida in July 2016. I will also give a talk at the National Institutes of Health in October 2016. We are planning to submit our first manuscript on chromosome aneuploidy by summer 2016.

Impacts
What was accomplished under these goals? Both animal husbandry and crop breeding depend on the reproductive health of organisms. One key feature of gametogenesis is the proper pairing and segregation of chromosomes during meiosis to form sperm and eggs in animals, gametophytes in plants and spores in fungi. Chromosome missegregation creates aneuploid gametes carrying the wrong numbers of chromosomes and is the leading cause of birth defects and mental retardation in humans and spontaneous abortion in animals. Interestingly, chromosome missegregation during meiosis occurs at higher rates in females while infertility is more likely to occur in males. To better understand these sex-specific "weak links" we use zebrafish because of its wide use as a model genetic organism and because of the economic importance of fish as a source of protein for feeding humans and livestock. The use of model genetic organisms over the last century has been critical in understanding the biology of reproductive health. Through our preliminary experiments we have identified mutations that sensitize females to form aneuploid embryos, while leaving males fertile. Another mutation we are studying causes females to undergo sex reversal and develop into fertile males. Clearly, these types of mutations could mimic the effects of exposure to genotoxic agents found in fertilizers, food storage containers and industrial waste products. The sensitivity of the fish also makes them a good candidate for characterizing the impact of climate change on reproductive health. Misdirection of resources that lead to increases in aneuploidy can have large economic consequences to the agricultural industry.

Publications

• Type: Journal Articles Status: Published Year Published: 2015 Citation: Schuster K, Leeke B, Meier M, Wang Y, Newman T, Burgess S, Horsfield JA. A neural crest origin for cohesinopathy heart defects. Hum Mol Genet. 2015 Dec 15;24(24):7005-16.
• Type: Journal Articles Status: Awaiting Publication Year Published: 2016 Citation: Chu DB, Burgess SM. A Computational Approach to Estimating Nondisjunction Frequency in Saccharomyces cerevisiae. G3 (Bethesda). pii: g3.115.024380.