Browsing by Subject "genetics"
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Item Early Life History and Resurgence of Snook (Family Centropomidae) in Texas(2012-07-16) Chapa, ChristopherThe resurgence of Texas' snook (Family Centropomidae) recreational fishery is coupled with an uncertainty as to what species occur in State waters, a limited understanding of life history, and habitat needs of its constituents. This study described species composition and early life history aspects of juvenile (< 100 mm SL) centropomids taken in bag seine collections in estuarine and freshwater habitats along the upper, middle, and lower coast of Texas during 2006 to 2010. Centropomus specimens (n = 548) captured from 41 locations across the Texas coast as well as congeners from Mexico (n = 24), Florida (n = 7), and Costa Rica (n = 3) were used in a genetics- and meristic-based determination of species composition, growth rates, range of hatching dates, geographic distribution, and habitat association. Genetic analyses of the mitochondrial DNA 16s ribosomal RNA gene and the mitochondrial control region (D - loop) validated the presence of smallscale fat snook (C. parallelus Poey, 1860, n = 333), common snook (C. undecimalis Bloch 1792, n = 212) and Mexican snook (C. poeyi Chavez, 1961, n = 3) in Texas, with the last of these validations representing the first known record of this species in Texas. AMOVA of 16s and D - loop sequences failed to detect genetic differentiation within Texas for C. parallelus and C. undecimalis. However, AMOVA for 16s and D - loop C. undecimalis sequences did yield significant genetic differences between Texas and Mexico against those from Florida and Costa Rica. Juvenile centropomids (< 100 mm SL) in Texas occupied backwater habitats with dissipated currents similar to those of Florida congeners (tidal sloughs, freshwater habitats, and structured shorelines). Coastal ranges of these species differed with C. parallelus taken from the Rio Grande to West Galveston Bay, whereas C. undecimalis was captured from the Rio Grande northward near Palacios. Three C. poeyi were captured at only two locations (Laguna Vista and Port Aransas). Daily growth rates varied between species and capture years, with these ranging from 0.22 to 0.97 mm d^-1. Analyses of hatch-date distribution suggest centropomids in Texas begin spawning in August and continue it through late September into mid-November.Item Elucidating the Functions of the Sialylation Pathway in Drosophila melanogaster(2012-10-19) Carnahan, MindySialylation is an important carbohydrate modification of glycoconjugates, which introduces sialic acids (SA). The relatively large nine-carbon, negatively charged sugars are typically located at the termini of carbohydrate chains. SA's are often required for functionally important molecular and cellular interactions including virus-host interactions, tumor progression and malignancy, immune system development and function, and nervous system development and function. However, the study of sialylation in vertebrates, including man, encounters serious obstacles associated with the complexity of vertebrates' biology and limitations of available experimental approaches. Drosophila is a useful model system with many advantages including quick generation time, a large number of progeny, simplified glycosylation and neurophysiology, and ease of genetic manipulations. The primary focus of this thesis is on the functions of Drosophila melanogaster CMP sialic acid synthetase (DmCSAS) and sialyltransferase (DSiaT) in the central nervous system (CNS). A combination of genetic, immunostaining, and neurobiology approaches were used to characterize the functions of DmCSAS and DSiaT in Drosophila. This investigation revealed the expression of DmCSAS and suggested that it plays an important role in a specialized and developmentally regulated process in the nervous system of Drosophila. Further experiments examined sub-cellular localization of DmCSAS revealing that this protein has a complex mostly Golgi-associated distribution within the cell in vivo. I discovered a novel link between Drosophila sialylation and circadian rhythm regulation. I also characterized the electrophysiological phenotypes of DmCSAS mutants and compared them to the corresponding defects associated with DSiaT mutations. My experiments also revealed that the relationship between DmCSAS and DSiaT are more complex than originally thought; these genes may have independent functions while also participating in the same pathway. Taken together, these results elucidate the sialylation pathway in Drosophila and shed more light on the role of sialylation in the nervous system. My experiments provide a unique evolutionary perspective on the sialylation pathway in animals and suggest that the neural function of SA in Drosophila can be conserved in vertebrates, including humans.Item Evaluation of udder and teat characteristics, calf growth, and reproduction in young Bos indicus-Bos taurus cows(Texas A&M University, 2008-10-10) Gladney, Cody JackSire and family effects were evaluated for calf growth, udder and teat conformation, and reproduction traits in 2- to 4- yr-old cows from the McGregor Genomics Project. Cows were produced by embryo transfer (ET) and natural service (NS) from the same 4 F1 Nellore-Angus sires, and were analyzed separately. Sire of cow was significant for calf birth weight (P = 0.014) among ET cows, but not NS cows. Among NS families, calves from cows out of Brahman-Hereford dams were 2.0 kg heavier (P = 0.064) at birth than calves from cows out of Brahman-Angus dams. Sire of cow accounted for variation in weaning weight (P = 0.006) and preweaning ADG (P = 0.005) of calves from ET dams, but not NS dams. Family nested within sire also accounted for variation (P = 0.061) in weaning weights of calves from ET dams. Sire of cow was significant for average teat length in ET (P < 0.001) and NS (P = 0.013) cows. Sire of cow was significant for average teat diameter (P = 0.022) among NS cows. Sire of cow also affected udder support score (P = 0.002), cow disposition at calf birth (P = 0.002), and cow weight at weaning (P = 0.045) in ET cows. Family and cow age also accounted for variation in cow disposition at calf birth (P = 0.015, P = 0.041, respectively) and cow weight at weaning (P = 0.001, P < .001, respectively) among ET cows. Calf year of birth also affected (P < .001) cow weight at weaning among ET cows. For NS dams, calf year of birth (P = 0.012), cow age (P < .001), and parity nested within cow age (P = 0.005) affected cow weight at weaning. Although reproduction data were not formally analyzed, there appear to be substantial differences for calving rate and average calving date among these cow families. Data from this project will be used for identification of genetic markers for these cow productivity traits.Item Functional Dissection of the Sensory Rays in Caenorhabditis elegans Male Mating Behavior(2012-02-14) Koo, Pamela KristineThe nematode Caenorhabditis elegans, with its sequenced genome, compact nervous system and stereotyped behaviors is an ideal model organism in which to study the integration of sensory input with motor output. Male mating behavior is among the most complex of these behaviors and males utilize a number of sensory organs in its execution. Among these are the rays, which are nine pairs of sensory organs that are arranged laterally along the male tail. Each ray is composed of two ultra-structurally distinct neuron types, an A type and a B type, surrounded by a glia-like structural cell. Though compositionally identical, each pair of rays maintains a unique, genetically-hardwired identity based on wiring, morphology, and neurotransmitter fate. Three techniques were used to investigate the role of the rays in male mating behavior. First, cauterization of the tips of the rays removed their sensory endings, leading to ray neuron death. Second, a heterologous light-activated cation channel was utilized to activate specific ray neuron types. Finally, ray neuron types were genetically targeted to undergo apoptosis by expression of heterologous caspases. The results show that the rays play important roles in multiple steps of male mating behavior, including contact response, scanning, and turning. The rays as a whole mediate posture change and backing during contact response. The ability to respond to hermaphrodite contact is shared among the rays, as is initiation of backward locomotion, though all rays are required for efficient, prolonged backward scanning. Both A and B neuron types appear capable of initiating contact response. Direct activation of B neurons through ChR2 causes a contact response-like ventral tail flexure, and elimination of both A and B neurons reduces contact response. A neurons additionally have a unique role in turning.Item Genetic analysis of canine hip dysplasia(Texas A&M University, 2007-04-25) Tsai, Kate LeanneThe morphologic variability seen in the domestic dog, Canis lupus familiaris, is unique among mammals. Selective pressures imposed by humans have divided dogs into almost 400 separate breeds. Selection has also led to the development of approximately 450 hereditary diseases, many of which are limited to specific breeds. Over half of these diseases present with similar clinical characteristics to those of many human hereditary diseases, making the dog an ideal model for study of the genetic bases of such diseases. Many diseases do not have candidate genes or have too many candidates to characterize. This is exacerbated in complex diseases that are caused by several genes. Whole-genome scans can provide insight into diseases by identifying marker(s) that co-segregate with a disease phenotype. The Minimal Screening Set - 2 (MSS-2) is the most recent set of microsatellites suitable for whole-genome screens. The first objective of this work was to streamline genomic screens in order to efficiently analyze large numbers of animals. To this end, chromosome-specific microsatellite panels were developed for the MSS-2. Canine hip dysplasia (CHD) is the most common orthopedic disease of the dog. CHD primarily affects medium and large breed dogs, but is found in almost every breed. The major objective of this work was to use linkage analysis to identify chromosomal regions that contain genes that are involved in CHD. Two populations were screened using the MSS-2. The first was a small family of Boykin Spaniels, though no markers were statistically significant in a whole-genome screen. An outcrossed pedigree of Greyhound/Labrador Retrievers was created for quantitative trait loci (QTL) mapping of CHD. The informativeness of markers in the F2 and backcrossed generations were calculated to show the utility of using such a population. Other factors that affect the power of this pedigree to identify QTL were also highlighted. Chromosomes that were identified in a previous screen as harboring putative QTLs were examined using the chromosome-specific panels to further define and confirm the regions of interest. Although no markers reached statistical significance, several areas of interest were identified.Item Genetic epidemiology and familial risk factors for paratuberculosis seropositivity in beef cattle(2009-05-15) Osterstock, Jason BarrettParatuberculosis is an intestinal infection of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). Genetic associations with paratuberculosis have been described in Holstein cattle. The objectives were to describe the association between paratuberculosis status of the dam and her offspring in beef cattle, develop methods to assess familial aggregation of paratuberculosis in cattle of unknown pedigree, and model the paratuberculosis status of beef cattle given familial and herdlevel covariates. Texas beef cattle were tested for paratuberculosis using serum antibody and microbiologic culture of feces. Available pedigree data were used to confirm familial relationships. The association between the paratuberculosis ELISA status of the dam and her offspring was assessed using mixed-effects models. Increased odds of being classified as a ?suspect? or greater based on ELISA results were observed if the dam was classified as a ?suspect? or greater. A positive linear association was observed between the ELISA value of the dam and her offspring. Analysis of pedigree data using conditional logistic regression identified ancestors associated with significantly increased odds of being classified as ?low positive? or greater. Microsatellite markers were used to classify cattle into genetically similar groups using allele frequency data. Nine clusters of genetically similar cattle were identified among paratuberculosis test positive cattle, herd matched controls, and pedigreed cattle. Clusters were validated using animals of known pedigree. Increased odds of paratuberculosis seropositivity were observed for some clusters compared to the cluster with the lowest seroprevalence. A predictive model was developed using a Bayesian framework to assess the association between antibody status of the dam and her offspring adjusted for herd-level risk factors. Predictors associated with highly probable increased odds of seropositivity included herd seroprevalence and herd fecal prevalence of MAP. The association between dam and offspring ELISA status was small (OR 1.35) and not highly probable. The results of this work support familial aggregation of paratuberculosis ELISA status, but herd-level risk factors appear to be more important in predicting ELISA status. A large proportion of observed serological reactions were not supported by fecal culture results; therefore, observed associations might be limited to humoral responses to Mycobacterium spp.Item Genetic relationships among Spiranthes parksii and congeneric species(Texas A&M University, 2007-04-25) Walters, CatherineUsing four AFLP markers and seven polymorphic microsatellite loci, we examined the genetic structure of the rare and endangered Spiranthes parksii Correll (Orchidaceae). Spiranthes parksii is not distinguishable from sympatric S. cernua (L.) Rich based on these data, though low levels of polymorphisms exist within both. These low levels of genetic diversity are likely a result of high levels of agamospermic reproduction through adventitious embryony. These results suggest that both S. parksii, as well as the sympatric, open flower form of S. cernua, are products of the more widely distributed S. cernua complex. Further, another local form of S. cernua, distinguished by its tendency to produce closed flowers is genetically distinct from both S. parksii, as well as the openflower form of S. cernua, as shown by AFLPs and microsatellite loci. This is the first known set of microsatellite primers developed specifically for use in Spiranthes. The application of these markers may be used to address other unresolved relationships among species of Spiranthes, many of which are also endangered or have populations in decline.Item Genetic relationships and evolutionary history of extant Bowhead whale populations, Balaena mysticetus(2009-05-15) Huebinger, Ryan MichaelBowhead whales, Balaena mysticetus, are large baleen whales that are characterized by an Arctic distribution. In order to provide proper management recommendations to the International Whaling Commission, a panel of twenty-five microsatellite markers was developed. This panel consisted of pure cytosine-adenine (CA) repeats and was selected for their ability to consistently amplify and for their consistency for allele designations. This panel was utilized to investigate stock structure within the Bering-Chukchi-Beaufort population of bowheads. Over thirty reports and manuscripts utilized these data for providing management recommendations to the International Whaling Commision. From this work it was concluded that there is presently one stock of bowhead whales within the Bering-Chukchi-Beaufort seas. This data was also utilized to examine the genetic relationships of the remaining extant bowhead populations. The microsatellite data, in combination with sequences from the mitochondrial control region and the NADH dehydrogenase subunit 1 (ND1) region, were used to examine population structure. The Okhotsk Sea was identified as the most divergent population of bowheads. Relationships among the extant populations demonstrated high levels of effective gene flow between populations. Gene flow appeared to be female-biased in relation to the Okhotsk Sea, whereas gene flow between Canada and the Bering-Chukchi-Beaufort populations appears to be equal between the bowhead whale sexes.Item Genomic analyses of induced hypercholesterolemia and atherosclerosis in a mixed breed colony of dogs and developmental abnormalities in the Havanese(2009-05-15) Starr, Alison NicoleThe domestic dog, Canis lupus familiaris, is a unique model system for the dissection of hereditary diseases. Selective breeding practices have created more than 300 distinct breeds of dogs, born from a desire to create specific physical and behavioral characteristics. Breeds represent closed breeding populations and the extensive records maintained for members of each breed (e.g., multi-generational pedigrees, veterinary medical records) present an incredible tool for genetic research. Two closed populations were used in the work presented here: a colony of mixed-breed dogs segregating resistance and sensitivity to cholesterol feeding, and a purebred pet population of Havanese experiencing a high frequency of developmental abnormalities. Estimates of heritability were calculated for each disease to evaluate the degree of phenotypic variation attributable to genetics among dogs in the populations used. A heritability of 0.55 (? 0.16) was identified for cholesterol resistance and sensitivity in the mixed-breed colony. The small sample size prevented the use of complex segregation analyses to examine mode of transmission. A heritability of 0.36 (? 0.26) was calculated for the composite phenotype in the Havanese, encompassing the spectrum of abnormalities in the breed. Polygenic inheritance was identified for the composite phenotype, but the action of a major gene was identified by complex segregation analyses in the Havanese. Complex diseases preclude the use of a candidate gene approach, owing to the multitude of genes involved in the disease process. Whole genome screens provide a practical approach to the identification of chromosomal region(s) associated with a disease phenotype by narrowing the search for candidate gene(s). The Minimal Screening Set ? 2 (MSS-2) was used in the present studies to evaluate the segregation of microsatellite markers in pedigrees for both the mixed-breed colony and the Havanese. No significant LOD scores were identified, though suggestive LOD scores were obtained in both analyses. A canine-specific oligonucleotide microarray was used to create gene expression profiles for developmental abnormalities in the Havanese and for cholesterol sensitivity in the mixed-breed colony dogs. Distinct expression profiles were generated for each group, and several genes of interest were identified as being both differentially expressed (>?2-fold change) and statistically significant (p-value<0.05).Item Genomic medicine in primary care: Texas physicians' adoption of an innovation(Texas A&M University, 2004-09-30) Suther, Sandra GayleNew applications of genomic medicine stemming from the Human Genome Project are predicted to become routine components of primary care. Primary care physicians (PCPs) will increasingly become responsible for screening patients for inherited diseases, recommending genetic testing, and making referrals to genetic services. Clinical applications of genomic medicine will occur at a variable pace. Characteristics of an innovation such as genomic medicine are strong indicators of its potential for adoption. The purpose of this study is to assess whether (and to what extent) physicians' perceptions of genomic medicine as an innovation influence their likelihood of adopting this innovation into primary care. The study's sample consists of 400 primary care physicians in Texas and employs a survey design. Based on Rogers' Diffusion of Innovations Theory, the perceived characteristics of genomic medicine - Relative Advantage, Compatibility, Complexity, Trialability, and Observability - are the study's independent/predictor variables. Likelihood of PCPs Adopting Genomic Medicine is the dependent variable. The nature of the social system (private or group practice) is examined as a possible moderator variable. The study suggests that Texas PCPs who are likely to adopt genomic medicine strongly perceive its clinical uses (such as genetic testing for carrier status or susceptibility to common diseases, testing an embryo for genetic disorders before it is implanted, and supplementing a family history) to be highly advantageous. For half of the PCPs, genetic services such as genetic counseling and genetic testing are not compatible with current practice. Perceived complexity of the innovation is the strongest predictor of likelihood of PCPs adopting genomic medicine. Many PCPs find it difficult to stay updated on genomic medicine and locate genetic services. Although Texas PCPs feel genomic medicine can be gradually incorporated into primary care practice, most are not presently observing their colleagues adopting genomic medicine or assisting their patients to make decisions regarding genetic services. Future efforts to advance the use of genomic medicine in primary care will require more emphasis on genetics in medical school curriculum and continuing education programs. Links with specialists trained in genetic counseling and health education will be essential to translate relevant information to patients and families.Item MicroRNA expression in canine mammary cancer(Texas A&M University, 2008-10-10) Boggs, Rene' MichelleMicroRNAs (miRNAs) play a vital role in differentiation, proliferation and tumorigenesis by binding to messenger RNAs (mRNA) and inhibiting translation. To initiate an investigation into the identification of miRNAs in the domestic dog, an emerging model for human disease, a comparison of the human and canine genetic databases was conducted. The bioinformatics work revealed significant conservation of miRNA genes between the two species. Proof of principle experiments, including serial dilutions and sequencing, were performed to verify that primers made to amplify human mature miRNAs can be used to amplify canine miRNAs, providing that the mature sequences are conserved. TaqMan? Real-time RT-PCR, a sensitive and specific method, was used to isolate the first miRNA mature products from canine tissues. The expression levels of miR-17-3p, miR-17-5p, miR-18, miR-19a, miR-19b, miR-20, and miR-92 were evaluated in five canine tissues (heart, lung, brain, kidney, and liver). Because miRNAs have been found to act as both tumor suppressors and oncogenes in several different cancers, expression patterns of ten miRNAs (miR-15a, miR-16, miR-17-5p, miR-21, miR-29b, miR-125b, miR-145, miR-155, miR-181b, let-7f) known to be associated with human breast cancer were compared between malignant canine mammary tumors (n=6) and normal canine mammary tissue (n=10). Resulting data revealed miR-29b and miR-21 to have a statistically significant (p<0.05) up-regulation in cancerous samples. Overall expression patterns showed nine of the ten miRNAs follow the same pattern of expression in the domestic dog as the human, while the miR-145 expression does not show a difference between the normal and cancerous samples.Item Phenotypic and Molecular Genetic Analysis of Reproductive Stage Heat Tolerance in Wheat (Triticum aestivum)(2011-08-08) Mason, Richard EstenHeat stress adversely affects wheat production in many regions of the world and is particularly detrimental during reproductive development. The objective of this study was to identify quantitative trait loci (QTL) associated with improved heat tolerance in hexaploid bread wheat (Triticum aestivum). To accomplish this objective, an analysis of both the phenotypic and genetic responses of two recombinant inbred line (RIL) populations was conducted. RIL populations Halberd x Cutter and Halberd x Karl 92 (H/K) both derive heat tolerance from Halberd and segregate in their response to heat stress. A heat susceptibility index (HSI) was calculated from the reduction of three yield components; kernel number, kernel weight, and single kernel weight, following a three-day 38 degrees C heat stress treatment during early grain-filling. The HSI, as well as temperature depression of the main spike and flag leaf were used as measurements of heat tolerance. Genetic linkage maps were constructed for both populations and were used in combination with phenotypic data and statistical software to detect QTL for heat tolerance. In a comparison across the two across populations, seven common QTL regions were identified for HSI, located on chromosomes 1B, 3B, 4A, 5A, 5B, and 6D. Subsequent analysis of temperature depression in the H/K population identified seven QTL that co-localized for both cooler organ temperature and improved HSI. Four of the beneficial alleles at these loci were contributed Halberd. The genetic effect of combining QTL, including QHkw.tam-1B, QHkwm.tam-5A.1, and QHskm.tam-6D showed the potential benefit of selection for multiple heat tolerant alleles simultaneously. Analysis of the H/K population in the field under abiotic stress detected QTL on chromosome 3B and 5A, which were in agreement with results from the greenhouse study. The locus QYld.tam-3B was pleiotropic for both temperature depression and HSI in both experiments and was associated with higher biomass and yield under field conditions. The results presented here represent a comprehensive analysis of both the phenotypic response of wheat to high temperature stress and the genetic loci associated with improved heat tolerance and will be valuable for future understanding and improvement of heat stress tolerance in wheat.Item Physiology and Genetics of Drought Tolerance in Cowpea and Winter Wheat(2012-02-02) Verbree, David 1977-In the wake of rising temperatures, erratic rainfall, and declining ground water table, breeding for drought tolerance in food crops has become a top priority throughout the world. Phenotyping a large population of breeding lines for drought tolerance is time-consuming and often unreliable due to multiple possible mechanisms involved. In cowpea (Vigna unguiculata L. Walp), a box-screening method has been used to partition the confounding effects that shoot and root traits have on drought tolerance by restricting root growth and providing a homogeneous soil moisture environment across genotypes. Nonetheless, multiple mechanisms of shoot drought tolerance have been reported which further complicate phenotyping. In winter wheat (Triticum aestivum L.), canopy temperature depression (CTD) has been proposed as a good indicator of drought tolerance. The recent development of low-cost thermal imaging devices could enable high-throughput phenotyping of canopy temperature. While CTD can be an indicator of overall plant water status, it can be confounded by high stomatal resistance, which is another seemingly contradictory mechanism of drought tolerance. The objectives of this study were to explore the physiological basis and genetics of the two mechanisms of shoot drought tolerance previously reported in cowpea and to develop and evaluate a method of high-throughput phenotyping of drought tolerance in winter wheat using thermal imaging. In cowpea, a legume well known for its tight stomatal control, no differences in gas exchange between drought tolerant and susceptible genotypes were observed. A unifoliate stay-green trait was discovered that segregates as a single recessive gene. However, it did not correlate with trifoliate necrosis or overall drought tolerance. In winter wheat, CTD did not always correlate with yield under rainfed conditions. One drought-tolerant cultivar, in particular, had the hottest canopy temperature, possibly because it was able to conserve moisture by closing its stomata whereas another closely related drought-tolerant cultivar had the coolest canopy temperature. Therefore, it appears that no single method of phenotyping for drought tolerance can be broadly applied across all genotypes of a given species due to possible contrasting mechanisms of drought-tolerance and environmental differences.Item The neuromolecular mechanisms that coordinate food availability with C. elegans male sexual behavior(2009-05-15) Gruninger, Todd RyanOrganisms must coordinate behavioral and physiological responses to changingenvironmental conditions. In the nematode C. elegans, the presence or absence of foodin the environment affects many metabolic and behavioral responses, including fathomeostasis, lifespan, and male mating. Specifically, male mating behavior normallyoccurs when a well-nourished male encounters a hermaphrodite, and is repressed if themale is under-nourished. To understand how environmental changes influence the driveto carry out specific behavioral tasks, I used C. elegans male mating as a model.Previously, mutants were isolated that display male mating behavior at inappropriatetimes, i.e. in the absence of mating cues. Loss of function mutations in the ERG K+channel, UNC-103, results in spontaneous seizures of the male sex muscles.Interestingly, I found that food deprivation can suppress unc-103(lf)-induced seizures,suggesting that pathways activated under this environmental condition can suppress theexcitability of the mating circuit.Using molecular, genetic, and behavioral assays, I identified sensory andmolecular mechanisms that reduce sex-muscle excitability under food-deprived conditions. I found that mutations that affect the muscular feeding organ, the pharynx,phenocopy the effects of food deprivation, and reduce sex-muscle excitability. Idemonstrated that mutations in the pharyngeal muscle protein, tropomyosin, cause thepharyngeal neurosecretory motor neurons (NSMs) to increase pharyngeal excitabilityand reduce sex-muscle excitability. Additionally, I found that olfactory neurons (AWCs)with sensory cilia exposed to the environment are up-regulated in the absence of foodstimuli, and also send inhibitory signals to the sex muscles. To determine howchemosensory and pharyngeal neurons in the head can signal to the genitalia, Ihypothesized that one mechanism could be via secretion of metabolic hormones. To testthis, I examined loss-of-function mutations in the insulin-like receptor, DAF-2, which isknown to regulate many behavioral and physiological responses to food. I demonstratedthat DAF-2 activity in the sex muscles is required for food-deprivation suppression ofunc-103(0)-induced seizures. I then identified components of a novel-insulin-like/DAF-2signaling pathway that reduces excitability. Specifically, I propose that ligand binding toDAF-2 activates PLC- and leads to increased cystolic Ca2+. This Ca2+ influx activatesCaMKII, which can phosphorylate/activate EAG-like K+ channels, thereby reducing cellexcitability.Item The Ribosomal DNA Genes Influence Genome-Wide Gene Expression in Drosophila melanogaster(2012-07-16) Paredes Martinez, Lida SilvanaChromatin structure is a fundamental determinant of eukaryotic gene expression and it is composed of two chromatin environments, euchromatin and heterochromatin. Euchromatin provides an accessible platform for transcription factors; hence it is permissive for gene expression. Heterochromatin on the other hand is highly compacted and inaccessible, which in most cases leads to transcriptional repression. A locus that is composed of both of these environments is the ribosomal DNA (rDNA). In eukaryotes the rDNA is composed of hundreds to thousands of tandemly repeated genes where maintaining both silent and active copies is fundamental for the stability of the genome. The aim of this research was to investigate the role of the rDNA in gene expression in Drosophila melanogaster. In D. melanogaster the rDNA loci are present on the X and Y chromosomes. This research used the Y-linked rDNA array to investigate the role of this locus on gene expression. A genetic and molecular strategy was designed to create and quantify specific, graded and isogenic Y- linked rDNA deletions. Then the deletions were used to address the effect of rDNA deletions on gene expression using reporter genes sensitive to Position Effect Variegation (PEV). In addition, the effect of the deletions in nucleolus size and structure as well as the effect of spontaneous rDNA deletions on gene expression were tested in this study. This research found that changes in rDNA size change the chromatin balance, which resulted in increased expression of the reporter genes, decreased nucleolus volume, and altered nucleolus structure. These findings prompted a further research question on whether this effect on gene expression occured globally in the genome. This was addressed by performing microarray analysis where the results showed that rDNA deletions affect about half of the genes on the genome. Presented in this dissertation is evidence that suggest a novel role for the rDNA is a global modulator of gene expression and also is a contributor to the gene expression variance observed in natural populations.