Doctor of Philosophy / Genetics Interdepartmental Program / Susan J. Brown / In Drosophila, all segments form in the blastoderm where morphogen gradients spanning the entire anterior-posterior axis of the embryo provide positional information. However, in the beetle Tribolium castaneum and most other insects, a number of anterior segments form in the blastoderm, and the remaining segments form sequentially from a posterior growth zone during germband elongation. In this work, I show that segmentation at both blastoderm and germband stages of Tribolium is based on a segmentation clock. Specifically, I show that the Tribolium primary pair-rule gene, Tc-even-skipped (Tc-eve), is expressed in waves propagating from the posterior pole and progressively slowing until they freeze into stripes; such dynamics are a hallmark of clock-based segmentation. Phase shifts between Tc-eve transcripts and protein confirm that these waves are due to expression dynamics. Such waves, like their counterparts in vertebrates, are assumed to arise due to the modulation of a molecular clock by a posterior-to-anterior frequency gradient. I provide evidence that the posterior gradient of Tc-caudal (Tc-cad) expression regulates the oscillation frequency of pair-rule gene expression in Tribolium. I show this by correlating the gradient of Tc-cad expression to the spatiotemporal dynamics of Tc-even-skipped expression in WT as well as in different knockdowns of Tc-cad regulators. Specifically, the spatial extent, frequency, and width of Tc-eve waves correlate with the spatial extent, expression level, and slope of Tc-cad gradient, respectively, as predicted by computer modeling. These results pose intriguing evolutionary questions, since Drosophila and Tribolium segment their blastoderms using the same genes but different mechanisms, and highlight the role of frequency gradients in pattern formation.

Doctor of Philosophy / Department of Division of Biology / Rollie J. Clem / Mosquitoes are carriers of a variety of harmful human pathogens, including viruses. In order to be successfully transmitted, a virus must evade mosquito immune responses. In this work, the innate immune role of apoptosis in mosquito-virus interactions was examined utilizing the disease vector Aedes aegypti and Sindbis virus. Ae. aegypti is the main vector for yellow fever and dengue virus, which result in over 100 million infections per year. Sindbis virus (Togaviridae) can be transmitted to vertebrates by Ae. aegypti in the laboratory. Sindbis is also well characterized molecularly, making it a good model system for understanding virus-vector interactions. Sindbis MRE-16 recombinant virus clones were utilized to express either an antiapoptotic or pro-apoptotic gene during virus replication. Mosquitoes were infected with recombinant virus clones during a blood meal or by intrathoracic injection. Midgut tissue and whole body samples were analyzed for virus infection and dissemination. Virus was also quantified in saliva and mosquito survival was assayed. Decreased infection in the midgut and delayed virus replication were observed in mosquitoes that were infected with virus expressing a pro-apoptotic gene. Infection with this virus clone also resulted in less virus in the saliva and reduced survival of infected mosquitoes. In addition, negative selection against pro-apoptotic gene expression during virus replication was observed. Collectively, these data suggest that apoptosis can serve as an antiviral defense in Ae. aegypti and may potentially be exploited to control virus transmission. An additional study included in this dissertation focused on zebrafish development and migration of somitic precursors from the tailbud. The tailbud consists of a population of stem cells at the posterior tip of the embryonic tail. The exit of these stem cells from the tailbud is required for the formation of tail somites. A novel double mutant was identified that lacked the t-box transcription factor spadetail and the BMP inhibitor chordin. Double mutants completely lacked somites and had an enlarged tailbud due to accumulation of stem cells that were unable to exit the tailbud. This study indicates the importance of BMP inhibition and spadetail expression in the proper exit of muscle precursors from the tailbud.

Master of Science / Department of Family Studies and Human Services / Bronwyn S. Fees / Research has determined three main pathways or orientations to happiness: Meaning, Pleasure, and Engagement (Peterson, Park, & Seligman, 2005). Each has shown to have a substantial impact on an individual's satisfaction with life. These orientations to happiness and their impact on life satisfaction were investigated among 342 emerging adults between the ages of 18-25 attending college. Linear multiple regression was conducted to assess the relationship between Life satisfaction and the three orientations of happiness after identifying the variance explained by demographics factors and personality traits. Results indicated first that each orientation to happiness was empirically distinguishable and related among the emerging adult population. Secondly, both Meaning and Pleasure were significant predictors of Life Satisfaction beyond the variance explained by personality; however, Engagement was not. Congruent with previous personality studies (Lykken & Tellegen, 1996; Lynn & Steel, 2006), life satisfaction was positively correlated with extraversion and negatively correlated with neuroticism. These findings indicate a need to understand how happiness and life satisfaction are filtered through a cultural, developmental, and academic lens. Further studies are necessary to determine the attitudes and behaviors in other countries, other life stages, and emerging adults not attending college.

Urban forests provide vital services to communities and are crucial for our mental, physical and emotional well-being. Recent research has shown that many variables at a neighbourhood-level are linked to variations in urban forest quantity, however, relationships at the property-level have not been considered. The purpose of this study was to examine the relationships at property-level in four socioeconomically varied neighbourhoods in the City of Mississauga (Ontario, Canada). Percent canopy cover and tree density was calculated using information from a survey, GIS datasets and remote sensing. Regression was used to determine which property-level characteristics are related to variations in the two tree cover variables. The results show that variables dealing with residents attitudes towards trees and space constraints are commonly linked to tree cover variations. The study found differences in relationships between the two tree measures at property-level and it provides greater insight into human-urban forest relationship at the micro-scale.

Deafness in early development can alter how the brain responds to sound, compromising the restoration of hearing with cochlear implants. We asked how the naïve brain responds to initial cochlear implant stimulation in children who are deaf. Results indicated large variability in initial responses. Deafness associated with GJB-2 mutations led to more uniformity in cortical responses than other etiologies. Responses associated with GJB-2 mutations were characterized by a response peak with large contributions from temporal and frontal regions of the brain. This response may reflect an early stage of auditory development. By contrast, another response type, typical of normal hearing children, received less contribution from frontal regions. Through consistent cochlear implant use, frontal regions of the brain may not be as strongly recruited. Effects of deafness in early development are heterogeneous, which may reflect differences in etiology of deafness and different stages of auditory development.

Urban forests provide vital services to communities and are crucial for our mental, physical and emotional well-being. Recent research has shown that many variables at a neighbourhood-level are linked to variations in urban forest quantity, however, relationships at the property-level have not been considered. The purpose of this study was to examine the relationships at property-level in four socioeconomically varied neighbourhoods in the City of Mississauga (Ontario, Canada). Percent canopy cover and tree density was calculated using information from a survey, GIS datasets and remote sensing. Regression was used to determine which property-level characteristics are related to variations in the two tree cover variables. The results show that variables dealing with residents attitudes towards trees and space constraints are commonly linked to tree cover variations. The study found differences in relationships between the two tree measures at property-level and it provides greater insight into human-urban forest relationship at the micro-scale.

Deafness in early development can alter how the brain responds to sound, compromising the restoration of hearing with cochlear implants. We asked how the naïve brain responds to initial cochlear implant stimulation in children who are deaf. Results indicated large variability in initial responses. Deafness associated with GJB-2 mutations led to more uniformity in cortical responses than other etiologies. Responses associated with GJB-2 mutations were characterized by a response peak with large contributions from temporal and frontal regions of the brain. This response may reflect an early stage of auditory development. By contrast, another response type, typical of normal hearing children, received less contribution from frontal regions. Through consistent cochlear implant use, frontal regions of the brain may not be as strongly recruited. Effects of deafness in early development are heterogeneous, which may reflect differences in etiology of deafness and different stages of auditory development.

Master of Science / Department of Family Studies and Human Services / Anthony Jurich / Throughout this report, I focused on the effects that the loss of a parent has on an adolescent during the various stages of adolescent development. Drawing upon research already completed on divorce during adolescence, I speculated on the similarities and differences between losing a parent through divorce or death during the adolescent stages of development. Loss by any means is tragic and life altering. However, as I attempted to illustrate, it was even more defining when encountered during the period of adolescence.

Master of Science / Department of Family Studies and Human Services / Rick J. Scheidt / This M.S. report provides an evaluative review of research on parental influences on adolescent sexual decision-making. Data show that a significant proportion of never-married female and male teens (ages 15-19) have had sexual intercourse at least once. Adolescent decisions on sexuality and possible consequences such as pregnancy or sexually-transmitted diseases may have profound personal and social impacts. Theoretical and empirical domains of parental influence are reviewed, including communication, morality, family structure and context, parental control, as well as the role of media. This review shows that adolescent sexuality has changed over time due to socio-historical factors and that parents continue to have an influence on their children’s decision-making abilities. Implications for applied professionals and researchers are discussed.

Master of Science / Department of Biology / Tonia L. Von Ohlen / The Drosophila embryonic nervous system develops from an array of neural precursor cells called, neuroblasts. These neuroblasts give rise to all the cell types that populate the mature central nervous system (CNS). The CNS originates from a bilateraly symmetric neurectoderm that is subdivided into three domains along the dorso-ventral (DV) axis. One of these domains is defined by the expression of the Homeodomain protein ventral nervous system defective (vnd). Regulation of neuroblast designation is very precise and controlled. Extensive research has been done on neuroblast formation along the anteroposterior axis, most of which indicates that neuroblast selection within a cluster of neurectodermal cells is controlled by segmentation genes. However, much more research is required to elucidate the function of genes along the DV axis. Early studies indicate that vnd is required for neuroblast formation in the ventral column. Here, we show that vnd function, but not expression, is dependent on MAPK activity downstream of Drosophila EGF-R (DER). Specifically, we show that vnd activity is eliminated in EGF-R mutant embryos in a stage specific manner by evaluating vnd’s ability to inhibit intermediate neuroblast defective (ind), muscle segment homeobox (msh), and the newly identified neural tube development player, neu3. Finally, we show that DER functionality in the ventral column is entirely dependent on the processing protein rhomboid (rho) in later stage embryos.