Alumni Dissertations and Theses

 
 

Alumni Dissertations and Theses

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  • The Expression of the Transcription Factor BROAD and RNA-binding Factors in the Midgut of the Mosquito Aedes Aegypti

    Author:
    Kathryn Ray
    Year of Dissertation:
    2013
    Program:
    Biology
    Advisor:
    James Nishiura
    Abstract:

    ABSTRACT Expression of the transcription factor BROAD and RNA binding factors in the midgut of the mosquito Aedes aegypti during metamorphosis by Kathryn Ray Thesis supervisor: James T. Nishiura, Associate Professor, Brooklyn College, CUNY Transcription factors, microRNAs and RNA binding factors frequently interact to coordinate gene expression during development. The transcription factor BROAD (BR) is a global regulator of insect gene transcription and governs the timing of the commitment to pupate. I determined BR expression in the Ae. aegypti midgut by qPCR, and correlated its expression with that of nine miRNAs and three RNA-binding factors. During midgut metamorphosis the expression of these factors was dynamic and reproducible. To better understand the changes in expression patterns, I evaluated the effects of hormone analogs on expression. Using this approach I uncovered concurrent up-regulation of BR, miR-34and miR-14 in the pupal midgut when treated with methoprene, and found that RH2485 accelerated expression of BR, BRAT, and microRNAs let-7 and miR-125. Treatment with each hormone analog resulted in a change in BR expression. Finally, I evaluated the effect of nutrients on expression levels. Surprisingly, though most transcripts were down-regulated during starvation, the expression of BR did not decrease, while microRNAs miR-34 and miR-14 were elevated. This may identify a novel role for during starvation in an invertebrate, and raises the possibility that miR-34 and miR-14 are part of a starvation-induced stress response in the mosquito midgut. In summary, this expression analysis suggests that microRNA regulation plays an important role during midgut metamorphosis, and reveals a new layer of regulatory complexity in the control of development in Ae. aegypti.

  • Systematics and evolution of Leandra s.str. (Melastomataceae, Miconieae)

    Author:
    Marcelo Reginato
    Year of Dissertation:
    2014
    Program:
    Biology
    Advisor:
    Fabian Michelangeli
    Abstract:

    Phylogenetic studies in the Melastomataceae have demonstrated the need of taxonomic rearrangements in the current classification. Melastomes are among the most diverse groups of plants and several cases of known artificial taxa are observed and awaiting further resolution. One example is the Leandra s.str. clade, which includes the majority of the taxa traditionally treated in the genus Leandra. Some attempts have been made to infer the relationships of Leandra s.str., but the sampling in these earlier studies was sparse and the resolution low inside the clade. The main objective here is to propose a comprehensive phylogenetic framework for this group to address evolutionary questions regarding morphology and biogeography. In Chapter 1, using a species tree approach, I present a phylogenetic hypothesis for Leandra s.str. and discuss incongruent patterns across gene trees and putative processes leading to them. The genus Leandra has been scarcely studied since a review in the 19th Century, and information such as overall distribution, anatomy, cytology, morphology, and even taxonomy is very limited. In Chapter 2, chromosome counts for some species of Leandra s.str. are provided, while in Chapter 6 a taxonomic review of Leandra sect. Leandra is presented and driven by the phylogenetic hypothesis of Chapter 1. The diversity and evolution of flowers in the Leandra s.str. clade is the topic of Chapter 3. Several question regarding the evolution of floral traits are addressed on a continuous framework using comparative phylogenetic methods. Leandra s.str. is nearly restricted to eastern Brazil, and the biogeography of the group is discussed in Chapters 4 and 5. In the former, I investigate disjunct patterns and distributional ranges and their relationship with climatic variables, focusing in the species that occurs outside eastern Brazil. In Chapter 5, I reconstruct the historical biogeography of Leandra s.str., proposing discrete biogeographical areas for ancestral distribution estimation, explore the climatic evolution and discuss the role of sympatry/allopatry in this group.

  • Phytosociology, History and Diversity in Farmer-Managed Landscapes on the Tonle Sap Floodplain, Cambodia

    Author:
    Andrew Roberts
    Year of Dissertation:
    2011
    Program:
    Biology
    Advisor:
    Christine Padoch
    Abstract:

    Driven by the annual flood pulse of the Tonle Sap Lake, the Tonle Sap floodplain in central Cambodia is a landscape characterized by dynamism, both ecological and social. Annual floods and rainfall vary in timing, duration and intensity from year to year. Patterns of burning, grazing, and agricultural expansion and contraction all leave their imprint on the landscape. While in the social domain, the region is likewise as complex. The genocidal, Maoist regime of Pol Pot darkened the 1970s. However, this was both preceded by, and followed by, years of civil war and social unrest. In recent years, Cambodia has shifted from a centrally-planned economy to a free-market economy, and experienced rapid economic growth followed by a dramatic slowdown. In the wake of such flux, the floodplains remain among the most productive rice-growing regions in the country, and are home to one of the most productive inland fisheries in the world. Even so, the region also remains one of the poorest. This project weaves analytical strands from ecology, geography and anthropology to delve into the ways in which people make a living in such a complex, challenging environment by focusing on the relationships between people, the landscape and plants. Results are presented from an analysis of 47 years of land use/land cover change depicted in aerial photography; an analysis of the structure and composition of floodplain plant communities through the use of descriptive ecological inventory; and an analysis of household-level natural resource-based livelihood activities, detailing how plant communities are utilized by village residents. A case study in floodplain land use is also presented, focusing on the Hillock-Depression Complex, a landscape element newly described herein. This case study illustrates the pitfalls of top-down land use planning in the context of a landscape rich in resources important to local residents but illegible to policy-makers. The results of these diverse analytical streams suggest that people do not live on the floodplain in spite of tremendous dynamism. Rather, the opposite is true. They live on the floodplain because of such dynamism, not as passive subjects but as active agents in generating diversity.

  • Drosophila Dunc-115 Mediates Axon Projection Through Actin Binding

    Author:
    Christopher Roblodowski
    Year of Dissertation:
    2011
    Program:
    Biology
    Advisor:
    He Qi
    Abstract:

    Axon pathfinding, the process of how neurons reach their correct targets during early neural development, is a critical area in neuroscience research. Though significant progress has been made in identifying the extracellular guidance cues and their membrane receptors, and possible downstream effectors including the Rho GTPases family, little is known regarding how guidance signals are relayed to the actin filaments that are central to the mobility of the growth cone. Our laboratory has identified and characterized Drosophila gene dunc-115 as a possible downstream target in relaying guidance cues further down to the cytoskeleton. Specifically, we have shown that Dunc-115 regulates neural connections in both the eye and the central nervous system in Drosophila. In this thesis, I have identified that (1) the surface receptor Roundabout (Robo) is an upstream regulator of guidance signals relayed through Dunc-115, (2) Dunc-115 receives signals from the Rho GTPases, and (3) Dunc-115 binds to actin via its VHD (Villin Head Piece) domain, suggesting a mechanism for Dunc115 to relay guidance signals. Finally, I have analyzed the genomic structure of the dunc-115 gene in 12 Drosophila genomes, which has generated further insights into how this gene has evolved.

  • Phylogeography, Phylogenetics, Historical Demography, and Morphology of Milksnakes (Genus Lampropeltis)

    Author:
    Sara Ruane
    Year of Dissertation:
    2013
    Program:
    Biology
    Advisor:
    Frank Burbrink
    Abstract:

    A primary goal for systematists is the discovery and identification of Earth's biodiversity. To meet these goals, coalescent-based phylogenetic and phylogeographic methods have been developed that help quantify diversity and provide a better understanding of processes generating species. Here, I use these methods to examine milksnakes (genus Lampropeltis ). Milksnakes are among the widest ranging of New World squamates and are frequently used as model organisms in Batesian mimicry studies. Despite this, there has been no research detailing their systematics within a molecular phylogenetic framework. Furthermore, previous molecular studies that include milksnakes have shown they do not form a monophyletic group within the genus and that color pattern, which has been the basis for their previous classification may not be informative with respect to evolutionary history. The study detailed here examines milksnakes across their intercontinental range to determine whether there is unrecognized diversity in this group. To meet this goal, I have developed a multi-locus dataset consisting of 11 nuclear genes and one mitochondrial gene. I use a molecular delimitation method to determine support for putative species, assess migration between species, and, within a species-tree framework, infer a phylogeny for the genus Lampropeltis , including all newly elevated milksnakes and all other recognized taxa within the genus. This dataset also provides the opportunity to examine how the inclusion of cryptic taxa and species tree methods provide a more accurate assessment of timing, rates and process of species diversification. After delimiting species, I use both non-genealogical and coalescent-based models to infer the historical demographic patterns of milksnakes. As the milksnake species identified here have representatives in both the temperate and tropical Americas, I am able compare demographic responses with respect to changes in effective population size between the Nearctic and Neotropical taxa. Specifically, I ask, do closely related milksnake species have similar demographic patterns resulting from Pleistocene glacial cycles despite their origination in the Neotropics or Nearctic. Results indicate that milksnakes do not share similar demographic patterns as a taxonomic group or by area and I conclude that authors should use caution in generalizing historical demographic trends based on geography. In addition to examining milksnakes using molecular data, I determine if there are detectable morphological differences independent of color pattern using geometric morphometrics. By taking photographs of 487 specimens, digitizing landmarks on their heads, and using geometric morphometric analyses, I determine that these types of analyses are useful in snake systematics for detecting distinct morphological shape variation among genetically delimited species, although they may not be powerful enough to use as an a priori species discovery tool.

  • ENHANCEMENT OF OLIGODENDROCYTE REMYELINATION THROUGH THE ABLATION OF NON-MUSCLE MYOSIN II B

    Author:
    Tomasz Rusielewicz
    Year of Dissertation:
    2013
    Program:
    Biology
    Advisor:
    Carmen Melendez Vasquez
    Abstract:

    The myelinating cell of the central nervous system, the oligodendrocyte (OL), undergoes a dramatic change in the organization of its cytoskeleton as it differentiates from an oligodendrocyte precursor cell to a myelin forming OL. This change involves an increase in branching, which is required for the OLs ability to myelinate multiple axons. Our laboratory has shown that levels of non-muscle myosin II (NMII), a regulator of cytoskeletal contractility, decrease as a function of differentiation and that inhibition of NMII activity increases branching and myelination of OL in coculture with neurons. It was also found that mixed glial cultures derived from NMIIB knockout mice display an increase in the number of mature myelin basic protein expressing OL compared to wild type cultures. These studies have now been extended to investigate the role of NMIIB ablation in myelin repair following focal demyelination by lysolecithin. To this end, we employed an OL-specific inducible knockout model using a PLP driven promoter in combination with a temporally activated CRE-ER fusion protein. The data indicate that conditional ablation of NMII in adult mouse brain, promotes faster lesion resolution and remyelination when compared to that observed in control brains. Although several pathways have been implicated in oligodendrocyte morphogenesis, their specific contribution to the regulation of NMII activity has not been directly examined. We tested the hypothesis that the activity of NMII in OPC is controlled by Fyn kinase via downregulation of RhoA-ROCK-NMII phosphorylation. The resulting data confirm the function of NMII as a negative regulator of OL maturation and demonstrate that Fyn kinase downregulates NMII activity thus promoting oligodendrocyte morphological differentiation. Furthermore this study provides a novel target for promoting myelin formation and repair in the adult brain.

  • RHYTHM DEVELOPMENT IN THE ZEBRA FINCH SONG

    Author:
    Sigal Saar
    Year of Dissertation:
    2009
    Program:
    Biology
    Advisor:
    Ofer Tchernichovski
    Abstract:

    When we listen to the zebra finch song, the song sounds very rhythmic and repetitive. Each bird has its own song rhythm. In order to study rhythm development in songbirds we introduced a new concept to bird song research, the quantification of rhythm and periodicity in song structure. By developing a technique that gives us insights into the song rhythm we have studied how song structure changes during different stages of the zebra finch life. We found that birds trained from an early age (day 43) exhibit two types of rhythm transformations: the first type is a smooth down-modulation of rhythm during several days of song development. The second type is an abrupt transition from one rhythm to a different rhythm. Smooth transitions might be caused by a slow shift in the timing of neuronal firing, while abrupt transitions might be caused by reorganization of the rhythm generator. We also examined why is it that zebra finches that are isolated until the end of their sensitive period and then trained do not imitate well. We discovered that their poor imitation correlates with inability to add new syllables to the songs. Zebra finches that sing a long motif before the onset of training were able to imitate better than finches with a short motif, perhaps because they have more raw materials to work with. Our findings suggest that at the end of the sensitive period vocal changes still occur, but imitation is constraint at the level of song rhythm and on the level of fine temporal structure.

  • Systematics and Biogeography of Orthaea Kloztsch (Ericaceae: Vaccinieae)

    Author:
    Nelson Salinas
    Year of Dissertation:
    2015
    Program:
    Biology
    Advisor:
    Paola Pedraza-PeƱalosa
    Abstract:

    In the first chapter a study of the distribution patterns of the neotropical Vaccinieae (Ericaceae) is presented. Five areas of endemism were recovered: Central America, northern Choco, southern Choco, eastern Ecuador, and Yungas. Divergence times estimations indicate that the Andean clade of Vaccinieae migrated to South America during the Late Oligocene or Early Miocene (28.9-17.84 MA), and most of the subsequent diversification took place during the Tertiary. The Yungas was the first Andean area to be colonized, and several dispersals towards the north expanded their distribution range. Both areas of endemism and dispersal events were influenced by geological processes, such as the raise of the Andes, the western Andean Portal, and the establishment of the Central America isthmus. The second chapter is a phylogenetic analysis of Orthaea Klotzsch (Vaccinieae: Ericaceae) based on molecular and morphological data. Orthaea is polyphyletic, with members evolving independently in several lineages within the tribe Vaccinieae. Currently accepted species of Orthaea s.l. were recovered within four clades: Guiana Shield, Empedoclesia, Thibaudia p.p., and Cavendishia + Orthaea p.p. clades. Most of the Andean species of Orthaea s.l. are closely related to Cavendishia, however, relationships within this clade were not strongly supported. Combined analyses of molecular and morphological data only provided support and uncovered synapomorphies for the Guiana Shield and Empedoclesia clades. Although a core Orthaea s.s. clade was identified, no nomenclatural changes are here proposed for the remainder species of Orthaea s.l. (20 spp.), except for those previously classified in Empedoclesia, a genus that needs to be reinstated. The third chapter is a taxonomic monograph of Orthaea s.s., as delimited in the combined phylogenetic analysis mentioned above. Fifteen species were studied, including two new species (O. eteocles N. R. Salinas and O. fissiflora N. R. Salinas & Pedraza) and a new synonym (O. glandulifera Luteyn = O. oedipus Luteyn).

  • Lipid dependence in Ras-driven tumors

    Author:
    Darin Salloum
    Year of Dissertation:
    2014
    Program:
    Biology
    Advisor:
    David Foster
    Abstract:

    Over past decade, metabolic alterations in cancer cells have received a substantial amount of interest. It had been established that cancer cells undergo a significant amount of metabolic alterations, and some of these alterations are similar to those in normal highly proliferative cells. However, it is becoming more apparent that many of the metabolic alterations are specific to particular oncogenic signaling pathways. Although altered metabolic machinery makes cancer cells more efficient at promoting growth when nutrients are supplied at the sufficient amounts, the dependency of cancer cells on particular metabolic reprogramming deems cancer cells susceptible to disruptions within metabolic network. Thus, the identification of metabolic weaknesses of cancer cells create a platform for therapeutic interventions. The conversion of normal cells to cancer cells involves a shift from catabolic to anabolic metabolism involving increased glucose uptake and the diversion of glycolytic intermediates into nucleotides, amino acids and lipids needed for cell growth. An underappreciated aspect of nutrient uptake is the utilization of serum lipids. We investigated the dependence of human cancer cells on serum lipids and report here that Ras-driven human cancer cells are uniquely dependent on serum lipids for both proliferation and survival. Moreover, Ras-driven cancer cells fail to adapt lipid metabolism upon lipid deprivation. Removal of serum lipids also sensitizes Ras-driven cancer cells to rapamycin. Suppressing pinocytosis in Ras-driven cancer cells similarly created sensitivity to suppression of mTORC1 - the mammalian/mechanistic target of rapamycin. The findings reported here reveal an enhanced need for serum lipids in Ras-driven human cancer cells that creates a synthetic lethal phenotype for suppressing mTORC1. While depriving humans of serum lipids is not practical, suppressing uptake of lipids is possible and could be exploited therapeutically, presenting speculated that this property displayed by Ras-driven cancer cells represents an Achilles' heel for the large number of human cancers that are driven by activating Ras mutations. mTOR has long been known to respond to amino acids, glucose and energy. However, lipids are another essential nutrient, and sensing mechanism on sufficiency of lipid precursors is not yet known. Based on the central position of PA in lipid biosynthesis, and its involvement in mTOR regulation, here we show that PA feeds into mTOR as a metabolite for sensing lipid precursors. In Ras-driven cells, PLD activity increase due to lipid withdrawal may be a mechanism to keep mTOR active during metabolic insufficiency stress.

  • Neonatal Involvement of the Serotonergic system in Hippocampal Wiring: Unraveling its role in Gender-Specific Mood Disorders

    Author:
    Sreyashi Samaddar
    Year of Dissertation:
    2013
    Program:
    Biology
    Advisor:
    Probal Banerjee
    Abstract:

    The hippocampus has been linked to a plethora of mood disorders. The monoamine neurotransmitter serotonin (5-HT) plays a critical role in the development of several of these mood and neuropsychiatric disorders. Serotonergic signaling via serotonin 1A receptor (5-HT1A-R) is crucial during the early postnatal days for later-life behavior, like anxiety and depression. Specifically, the forebrain 5-HT1A-R heteroreceptors have been implicated in several mood disorders. Intriguingly, the incidence of mood disorders is two-fold higher in women than men. Furthermore, the level of the serotonin 1A receptor (5-HT1A-R) is significantly higher in the brain of women than men, suggesting that the women may be more sensitive to a deficiency in 5-HT1A-R signaling. Taken together, all these studies also suggest that the serotonergic system operating via 5-HT1A-R in brain development may determine behavioral manifestation of mood disorders in adulthood. However, the mechanistic details of the 5-HT1A-R signaling pathway, especially how it operates in early developmental stages, are still unclear. The current study is aimed at bridging this gap. Current findings reveal that 5-HT1A-R signaling acting through PKC epsilon and Erk1/2 augments neuroproliferation and neurogenesis in the dentate gyrus (DG) in mice at postnatal day-6 (P6), which marks the peak of postnatal neuroproliferation. However, only the basal level of neuroproliferation was significantly stunted in the female but not male 5-HT1A-R (-/-) (KO) mice at P6. Subsequently, the neuroproliferation in the KO female mice could be restored to almost wild-type (WT) levels through the stimulation of the downstream PKC epsilon molecule using a selective activator, DCP-LA. Using Timm staining, a significant increase was observed in the arborization of the DG granule cell-derived mossy fiber (MF) axons and their connectivity with the CA3 pyramidal cells in the Stratum Oriens (SO) region in the female KO mice at P18. Such increased MF connectivity could lead to increased excitation and elevated anxiety. Confirming the importance of the identified signaling activity through PKC epsilon, this increased MF connectivity was restored to normal levels in the KO females treated with DCP-LA from P6-14. Finally, this treatment eliminated the significantly elevated anxiety levels in the adult female KO mice. Thus, a sex-specific effect of serotonergic signaling via the 5-HT1A-R plays an important role in hippocampal development and later-life behavior, which can be corrected by targeting a downstream signaling molecule, PKC epsilon. New-born and immature granule cells of the DG are resistant to inhibition by gamma-aminobutyric acid (GABA), and each granule cell-derived MF axon connects with about 50 inhibitory inter-neurons, which cause inhibition of the CA3 pyramidal neurons. In contrast, each MF axon connects directly with only 10-14 CA3 pyramidal neurons. Thus, the MF axons, especially the excitatory immature granule neurons, produce more feed-forward inhibition than excitation, which allows for only a limited level of activation of the CA3 neurons. Decreased neuroproliferation at P6 would yield less GABA-insensitive new granule neurons in the DG, which may then lead to a decrease in feed-forward inhibition, thereby eliciting an overall increase in excitation of the CA3 pyramidal neurons and the downstream Schaffer Collateral pathway of the hippocampus. While this may explain the extension of MF collaterals in the SO region, the sex-specific effect of 5-HT1A-R deficiency on neuroproliferation remains to be explained. Although sex-based differences have yet to be recorded for steroid levels in the neonatal hippocampus, it is known that neonatal neuroproliferation in the DG is significantly higher in male mice, and estradiol treatment boosts neuroproliferation only in the females. This study introduces the serotonergic system as a second signaling scheme with pronounced sex-specific effects in the neonatal DG and suggests a possible crosstalk between brain steroids and 5-HT during brain development. Current findings reveal that 5-HT1A&ndashR signaling acting through PKC epsilon and Erk1/2 augments neuroproliferation and neurogenesis in the dentate gyrus (DG) in mice at postnatal day-6 (P6), which marks the peak of postnatal neuroproliferation. However, only the basal level of neuroproliferation was significantly stunted in the female but not male 5-HT1A&ndashR (-/-) (KO) mice at P6. Subsequently, the neuroproliferation in the KO female mice could be restored to almost wild-type (WT) levels through the stimulation of the downstream PKC epsilon molecule using a selective activator, DCP-LA. Using Timm staining, a significant increase was observed in the arborization of the DG granule cell-derived mossy fiber (MF) axons and their connectivity with the CA3 pyramidal cells in the Stratum Oriens (SO) region in the female KO mice at P18. Such increased MF connectivity could lead to increased excitation and elevated anxiety. Confirming the importance of the identified signaling activity through PKC epsilon, this increased MF connectivity was restored to normal levels in the KO females treated with DCP-LA from P6-14. Finally, this treatment eliminated the significantly elevated anxiety levels in the adult female KO mice. Thus, a sex-specific effect of serotonergic signaling via the 5-HT1A-R plays an important role in hippocampal development and later-life behavior, which can be corrected by targeting a downstream signaling molecule, PKC epsilon. New-born and immature granule cells of the DG are resistant to inhibition by gamma-aminobutyric acid (GABA), and each granule cell-derived MF axon connects with about 50 inhibitory inter-neurons, which cause inhibition of the CA3 pyramidal neurons. In contrast, each MF axon connects directly with only 10-14 CA3 pyramidal neurons. Thus, the MF axons, especially the excitatory immature granule neurons, produce more feed-forward inhibition than excitation, which allows for only a limited level of activation of the CA3 neurons. Decreased neuroproliferation at P6 would yield less GABA-insensitive new granule neurons in the DG, which may then lead to a decrease in feed-forward inhibition, thereby eliciting an overall increase in excitation of the CA3 pyramidal neurons and the downstream Schaffer Collateral pathway of the hippocampus. While this may explain the extension of MF collaterals in the SO region, the sex-specific effect of 5-HT1A-R deficiency on neuroproliferation remains to be explained. Although sex-based differences have yet to be recorded for steroid levels in the neonatal hippocampus, it is known that neonatal neuroproliferation in the DG is significantly higher in male mice, and estradiol treatment boosts neuroproliferation only in the females. This study introduces the serotonergic system as a second signaling scheme with pronounced sex-specific effects in the neonatal DG and suggests a possible crosstalk between brain steroids and 5-HT during brain development.