Cell Biology & Molecular Genetics Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2750
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Item Development and the Early Animal Fossil Record: Evolution and Phylogenetic Applications(2016) Tweedt, Sarah Maureen; Delwiche, Charles F; Erwin, Douglas H; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although evolutionary developmental biology and paleontology are linked by the study of morphology, the application of development to paleontological questions has only recently become more prominent. The growth of a robust developmental genetic framework for studying the origin and evolution of morphological features, however, holds great promise for understanding ancient animal life. As paleontology provides the historical record as well as the temporal and environmental context of past morphological evolution, uniting knowledge of developmental genetic systems with this historical record will form a key synthetic approach to understanding the early evolution of developmental processes. Ultimately unraveling the sequence of ancient animal developmental evolution will require combining analysis of comparative developmental data, critical assessment of fossil morphology within a developmental framework, and the targeted exploration of specific geologic periods to fill in the missing record of key times in animal developmental evolution. This study addresses each of these three approaches. First, I provide a new compilation and evaluation of recent comparative and experimental developmental biology data to review the nature of developmental ‘toolkits’ at the origin of the most basal animal clades. I reconstruct early animal developmental capacities and integrate these data within a temporal framework to better understand the context of earliest animal development. Second, I assess longstanding evolutionary hypotheses about the origin of the panarthropod clade and the phylogenetic position of Cambrian ‘lobopod’ fossils by examining signal present within current morphological datasets. I apply new methods to fossil panarthropod phylogeny estimation and suggest strategies for developmentally-informed phylogenetic coding of morphological data. Third, I present the discovery of the oldest spicule-bearing fossil sponges in the rock record, which co-occur in latest Ediacaran strata with classic enigmatic Ediacaran fauna. I provide a formal systematic description of fossil material from localities in both Nevada and southern Namibia. The combined approaches presented herein are a first step towards a deeper integration of developmental principles in the study and discovery of ancient animal life, and contribute to our understanding of the evolution of ancient animal developmental processes.Item Evolution of Pair-rule genes(2015) Lu, Yong; Pick, Leslie; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)All insects have a segmented body. The genes controlling segment development have been well characterized in the fruit fly, Drosophila melanogaster. These genes were divided into three categories: gap genes specify several continuous segments over a broad region of the embryo; Pair-Rule Genes (PRG) are responsible for segment formation and are the first set of genes to be expressed in repetitive patterns in the embryo; Segment polarity genes define anterior and posterior polarities within each segment.To understand how PRGs evolve, I took a comparative approach in this thesis. First, I compared the function of the Drosophila PRG ftz-f1 to that of its mammalian orthologs by expressing them all in Drosophila embryos. I found that the molecular function of this family of nuclear receptors has been highly conserved during evolution. Next, I set out to establish new insect model systems to study PRG function. While, some PRGs have been studied in other insects, most of these studies focused on holometabolous insects. My work focused on the sister group to the holometabolous insects, the Hemipteroid Assemblage. I participated in the genome annotation of a hemipteras insect, Oncopeltus fasciatus. I annotated nuclear receptor super family, Hox and PRGs in Oncopeltus. I further studied the expression and function of four PRGs in Oncopeltus. Using in situ hybridization and RNAi, I found that, Of-ftz and Of-hairy do not have segmentation function, while Of-ftz-f1 has function in oogenesis and segmentation. Of-runt was found to induce cell death in oocytes, but its function in segmentation needs further analysis. Using the knowledge and expertise I gained from Oncopeltus, I successfully set up in situ hybridization, antibody staining and parental RNAi in an invasive hemipteran insect pest, the Brown Marmorated Stink Bug (BMSB) Halyomorpha halys. These studies show that the expression and function of PRGs varies extensively in diverse insects, despite the overall conservation of a segmented body plan.Item Evolution of sex-biased expression in Caenorhabditis(2011) Thomas, Cristel Gwenola; Haag, Eric S; Molecular and Cell Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mating systems have a profound impact on genome structure evolution, both indirectly through their effects on population genetics and directly due to the genetic control of reproductive traits. Most extant Caenorhabditis species are gonochoristic (males and females), while the most studied species, C. elegans and C. briggsae, are androdioecious (self-fertile hermaphrodites and males). The latter two species display an overall reduced ability to mate, suggesting that the selective pressure on maintaining efficient mating was weakened as selfing arose. The genes underlying these traits were likely to have been expressed in a sex-biased fashion in the gonochoristic ancestor, and we hypothesized that as selfing emerged their regulation was modified or they were lost altogether. This hypothesis is especially interesting given that selfing species have consistently smaller genome sizes than their gonochoristic relatives. I sought to address whether a disproportionate loss of genes with sex-biased expression accompanies the loss of mating-related traits in Caenorhabditis hermaphrodites. I first examine sex-biased expression in a gonochoristic species, C. remanei, and identify genes with highly sex-biased expression. I find that these genes are more likely to be missing in selfing species than expected by chance. I then select some of these genes based on their phylogenetic conservation patterns in the genus, and characterize them more thoroughly to shed some light on their functions. Through this study I identify a novel male-associated candidate cis-regulatory element. Lastly, I broaden the scope of the study by determining transcriptome wide sex-biased expression patterns in four Caenorhabditis species. I confirm that C.elegans displays a decrease in the proportion of strong female-biased expression, as well as a modification of the expression of genes with male-biased expression both in males and in hermaphrodites, when compared to gonochoristic Caenorhabditis. Taken together, this study illustrates the transcriptomic consequences of a modification of the mating system, and begins to address its effect on genome structure.