In mammals, newly synthesized proteins destined for secretion are translocated cotranslationally into the lumen of the Endoplasmic Reticulum (ER). Once inside, these nascent polypeptide chains are bound by a lumenal ER protein called BiP (Immunoglobulin Binding Protein) or Grp 78 (Glucose Regulated Protein 78). It is hypothesized that this binding is necessary to protect the nascent chains until they are properly folded or assembled with other subunits. When the proteins are folded and assembled, they are released from BiP by a process that is dependent on ATP hydrolysis. Since ATP is synthesized mainly in the mitochondria, we hypothesized that there must be an ATP transporter in the ER which would allow the protein mediated transport of ATP from the cytosol into the ER lumen. We studied the transport of ATP in vitro and found that ATP enters the lumen of the ER in a saturable manner with a Kmapp~3μM. ATP transport is dependent on time, protein, and vesicle integrity, it is also inhibited by the general anion transport inhibitor, 4,4' diisothiocyano-2,2'-disulfonic acid stilbene (DIDS). We also found that the transport was inhibited by membrane impermeable protein modifying agents such as N-ethlymaleamide (NEM) and Pronase when added to intact ER vesicles. These results suggest that the transport is mediated by a protein with an active cytoplasmic face. Using monoclonal and polyclonal antibodies to BiP and Grp94 (another resident ER protein) and U.V. crosslinking, we demonstrated that after transport of ATPα32P into intact vesicles, radiolabeled BiP and Grp94 could be immunoprecipitated. We also found that labeling of lumenal proteins with ATP is dependent on the transport of ATP. Finally using ATP labeled with 35S, we concluded that BiP was able to bind intact ATP and we confirmed earlier work that BiP was thiophosphorylated while Grp94 is not. The second area of study involves processes that occur further along the secretory pathway in the Golgi apparatus. It was known from previous work that the nucleotide sugar substrates necessary for the synthesis of the linkage region, UDP-xylose (UDP-Xyl), UDP-galactose (UDP-Gal) and UDP-glucuronic acid (UDP-GlcA) were transported into the Golgi apparatus from the cytosol via protein mediated transporters. In order to eventually purify one of these transporter proteins, we wanted to reconstitute their activities. We were able to reconstitute the activities that exhibited kinetic parameters and inhibitor sensitivities very similar to those seen in intact Golgi vesicles. In the case of UDP-xylose it was necessary to prepare the liposomes using endogenous Golgi lipids in order to get transport activity similar to that seen in the intact Golgi vesicles. This suggested a specific lipid requirement for the UDP-xylose transporter. These transporters seem to be antiporters, whereby the nucleotide sugar enters the lumen of the Golgi coupled to the equimolar exit of the corresponding nucleoside monophosphate (Hirschberg, C.B. and Snider, M.D. 1987). We also showed that we could reproduce the hypothesized antiporter system in the reconstituted proteoliposomes by preloading the proteoliposomes with the putative antiporter molecule UMP. The rationale for developing the reconstituted system is eventually to use this system to purify one of these nucleotide sugar translocators. In the last set of studies, I have shown that this reconstituted system can be used to monitor the purification of the UDP-galactose translocator. Using column chromatography we were able to purify this membrane translocator protein 45,000 fold from a rat liver homogenate.

The Smad proteins transduce the signal of transforming growth factor-β (TGF-β) and related factors from the cell surface to the nucleus. Following C-terminal phosphorylation by a corresponding receptor kinase, the R-Smad proteins form heteromeric complexes with Smad4. These complexes translocate into the nucleus, bind specific transcriptional activators and DNA, ultimately modulating gene expression. Though studied through a variety of means, the stoichiometry of the R-Smad/Smad4 complex is unclear. We investigated the stoichiometry of the phosphorylation-induced R-Smad/Smad4 complex by using acidic amino acid substitutions to simulate phosphorylation. Size exclusion chromatography, analytical ultracentrifugation, and isothermal titration calorimetry analysis revealed that the R-Smad/Smad4 complex is a heterotrimer consisting of two R-Smad subunits and one Smad4 subunit. In addition, a specific mechanism for phosphorylation-induced R-Smad/Smad4 complex formation was studied. Although it had been previously established that part of the mechanism through which phosphorylation induces Smad oligomerization is through relieving MH1-domain mediated autoinhibition of the MH2 (oligomerization) domain, it is also evident that phosphorylation serves to energetically drive Smad complex formation. Through mutational and size exclusion chromatography analysis, we established that phosphorylation induces oligomerization of the Smads by creating an electrostatic interaction between the phosphorylated C-terminal tail of one R-Smad subunit in a Smad trimer with a basic surface on an adjacent R-Smad or Smad4 subunit. The basic surface is defined largely by the L3 loop, a region that had previously been implicated in R-Smad interaction with the receptor kinase. Furthermore, the Smad MH2 domain shares a similar protein fold with the phosphoserine and phosphothreonine-binding FHA domains from proteins like Rad53 and Chk2. Taken together, these results suggest that the Smad MH2 domain may be a distinct phospho serine-binding domain, which utilizes a common basic surface to bind the receptor kinase and other Smads, and takes advantage of phosphorylation-induced allosteric changes dissociate from the receptor kinase and oligomerize with other Smads. Finally, the structural basis for the preferential formation of the R-Smad/Smad4 heterotrimeric complex over the R-Smad homotrimeric complex was explored through X-ray crystallography and isothermal titration calorimetry. Crystal structures of the Smad2/Smad4 and Smad3/Smad4 complexes revealed that specific residue differences in Smad4 compared to R-Smads resulted in highly favorable electrostatic interactions that explain the preference for the interaction with Smad4.

In 2008 the Nobel Prize in Physiology or Medicine was awarded to the co-discoverers of the Human Immunodeficiency Virus Type 1 (HIV-1), the causative agent of Acquired Immunodeficiency Syndrome (AIDS). This award acknowledged the enormous worldwide impact of the HIV-1/AIDS pandemic and the importance of research aimed at halting its spread. Since the syndrome was first recognized, 25 million people have succumbed to AIDS and over 33 million are currently infected with HIV-1 (www.unaids.org). The most effective strategy for ending the pandemic is the creation of a prophylactic vaccine. Yet, to date, all efforts at HIV-1 vaccine design have met with very limited success. The consistent failures of vaccine candidates stem in large part from the unprecedented diversity of HIV-1. Among the novel theories of vaccine design put forward to address this diversity is the targeted vaccine approach. This proposal is based on the finding that mucosal transmission of HIV-1, the most prevalent form, occurs across a selective bottleneck such that typically only a single (or a few) variants of the viral swarm present in a donor are passed to the recipient. While the mechanisms controlling the selection are largely unknown, the targeted vaccine approach postulates that once they are identified, we can utilize this understanding to design vaccines specifically targeted to the characteristics shared by the rare, mucosally transmissible HIV-1 variants. The studies described in this work were conducted to improve our understanding of the factors influencing viral variant selection during mother-to-child-transmission of HIV-1, a route of mucosal transmission which has globally become the leading cause of child infection. A unique panel was generated, consisting of nearly 300 HIV-1 envelope genes cloned from infected mother-infant pairs. Extensive characterization of the genotypes, phenotypes and phylogeny of these clones was then done to identify attributes differentiating early infant from maternal variants. Low genetic diversity of HIV-1 envelope variants was detected in early infant samples, suggesting a bottleneck and active selection of variants for transmission. Transmitted variants did not differ from non-transmitted variants in CD4 and CCR5 use. Infant isolates replicated poorly in macrophages; a cell subtype hypothesized to be important in the establishment of infection. The sensitivity of infant envelope variants to neutralization by a panel of monoclonal antibodies, heterologous and autologous plasmas and HIV-1 entry inhibitors varied. Most intriguingly, envelopes cloned from infants infected during delivery exhibited a faster entry phenotype than maternal isolates. Together, these findings provide further insight into viral variant selection during mother-to-child transmission. Identification of properties shared by mucosally transmitted viral variants may allow them to be selectively targeted, resulting in improved methods for preventing HIV-1 transmission.

Magnetic resonance imaging (MRI) has emerged as the imaging modality of choice in a wide variety experimental and clinical applications. In this dissertation, I will describe novel MRI techniques for the characterization of neural and pulmonary vascular function in preclinical models of disease. In the first part of this dissertation, experimental results will be presented comparing the identification of ischemic lesions in experimental stroke using dynamic susceptibility contrast (DSC) and a well validated arterial spin labeling (ASL). We show that DSC measurements of an index of cerebral blood flow are sensitive to ischemia, treatment, and stroke subregions. Further, we derived a threshold of cerebral blood flow for ischemia as measured by DSC. Finally, we show that ischemic lesion volumes as defined by DSC are comparable to those defined by ASL. In the second part of this dissertation, a methodology of visualizing clots in experimental animal models of stroke is presented. Clots were rendered visible by MRI through the addition of a gadolinium based contrast agent during formation. Modified clots were used to induce an experimental embolic middle cerebral artery occlusion. Clots in the cerebral vasculature were visualized in vivousing MRI. Further, the efficacy of recombinant tissue plasminogen activator (r-tPA) and the combination of r-tPA and recombinant annexin-2 (rA2) was characterized by clot visualization during lysis. In the third part of this dissertation, we present results of the application of hyperpolarized helium (HP-He) in the characterization of new model of experimental pulmonary ischemia. The longitudinal relaxation time of HP-He is sensitive to the presence of paramagnetic oxygen. During ischemia, oxygen exchange from the airspaces of the lungs to the capillaries is hindered resulting in increased alveolar oxygen content which resulted in the shortening of the HP-He longitudinal relaxation time. Results of measurements of the HP-He relaxation time in both normal and ischemic animals are presented. In the final part of this dissertation, I will present results of a new method to measure pulmonary blood volume (PBV) using proton based MRI. A T1 weighted, inversion recovery spin echo sequence with cardiac and respiratory gating was developed to measure the changes in signal intensity of lung parenchyma before and after the injection of a long acting intravascular contrast agent. PBV is related to the signal change in the lung parenchyma and blood before and after contrast agent. We validate our method using a model of hypoxic pulmonary vasoconstriction in rats.

Molecular recognition, defined as the specific interactions between two or more molecules, is at the center of many biological processes including catalysis, signal transduction, gene regulation and allostery. Allosteric regulation is the modification of function caused by an intermolecular interaction. Allosteric proteins modify their activity in response to a biological signal that is often transmitted through the interaction with a small effector molecule. Therefore, determination of the origins of intermolecular interactions involved in molecular recognition and allostery are essential for understanding biological processes. Classically, molecular recognition and allosteric regulation have been associated to structural changes of the system. NMR spectroscopic methods have indicated that changes in protein dynamics may also contribute to molecular recognition and allostery. This thesis is an investigation of the contributions of both structure and dynamics in molecular binding phenomena. In chapter I, I describe molecular recognition, allostery and examples of allostery and cooperativity. Then I discuss the contribution of protein dynamics to function with a special focus on allosteric regulation. Lastly I introduce the hemoglobin homodimer, HbI of Scapharca inaequivalvis and the mRNA binding protein TIS11d. Chapter II is the primary focus of this thesis on the contribution of protein dynamics to allostery in the dimeric hemoglobin of scapharca inaequivalvis, HbI. Thereafter I concentrate on the mechanism of adenine recognition of the Tristetraprolin-like (TTP) protein TIS11d; this study is detailed in Chapter III. In Chapter IV I discuss broader impacts and future directions of my research. This thesis presents an example of the use of protein NMR spectroscopy to probe ligand binding. The studies presented in this thesis emphasize the importance of dynamics in understanding protein function. Measurements of protein motions will be an element of future studies to understand protein function in health and disease.

Repair of DNA double-strand breaks via homologous recombination is an essential pathway for vertebrate cell development and maintenance of genome integrity throughout the organism’s lifetime. The Rad51 enzyme provides the central catalytic function of homologous recombination while many other proteins are involved in regulation and assistance of Rad51 activity, including a group of five proteins referred to as Rad51 paralogs (Rad51B, Rad51C, Rad51D, Xrcc2, Xrcc3). At the start of my work, cellular studies of human Rad51 (HsRad51) had shown only that it forms distinct nuclear foci in response to DNA damage. Additionally, no information regarding the cellular localization, potential DNA damage-induced redistribution or cellular functions for any of the Rad51 paralog proteins was available. Therefore, the goals of this work were to (1) present a more complete description of the cellular localization and DNA damage-induced redistribution of Rad51 and the two paralog proteins known to specifically associate with Rad51, Rad51C and Xrcc3, and (2) to define specific functional roles for Rad51C and Xrcc3 in mediating Rad51 activity. I focused on the use of cellular, RNAi and immunofluorescence methods to study endogenous Rad51, Rad51C and Xrcc3 in human cells. In my initial studies we showed for the first time that Xrcc3 forms distinct foci in both the nucleus and cytoplasm independent of DNA damage, that the distribution of these foci did not change significantly throughout the time course of DNA damage and repair, and that Xrcc3 focus formation is independent of Rad51. Additionally, and unlike most previously published images of nuclear Rad51, we found that the majority of DNA damage-induced nuclear Rad51 foci do not colocalize with gamma H2AX, a histone marker used to indicate the occurrence of DNA double strand breaks. As a consequence of these initial outcomes, a significant amount of effort was devoted to developing and optimizing immunofluorescence methods. Importantly, we developed a purification method for commercially available monoclonal antibodies against Rad51C and Xrcc3 that significantly improved their reactivity and specificity. My next study concentrated on Rad51C. Similar to Xrcc3, we found for the first time that Rad51C forms distinct nuclear and cytoplasmic foci independent of DNA damage and Rad51. An additional and surprising outcome was our discovery that Rad51C plays an important role in regulating the ubiquitination and proteasome-mediated degradation of Rad51. While biochemical functions for Rad51 paralog proteins had been suggested in the literature, this was the first demonstration of a specific biochemical function for Rad51C that contributes directly to the Rad51 activity in the homologous recombination pathway. Our improved immunofluorescence methods allowed us to see the accumulation of Rad51, Rad51C and Xrcc3 at the nuclear periphery early in response to DNA damage, suggesting the existence of a DNA damage-dependent trafficking mechanism that promoted movement of these proteins from the cytoplasm to the nucleus. This led to further studies in which we show distinct co-localization of cytoplasmic Rad51 with actin as well as alpha and beta tubulin. Using both immunofluorescence and sub-cellular fractionation methods our recent results strongly suggest that trafficking of Rad51 to the nucleus in response to DNA damage is regulated at least in part by its association with cytoskeletal proteins, and involves movement of both existing pools of Rad51 and newly synthesized protein. In a particularly exciting development, in collaboration with Leica Microsystems and Dr. Joerg Bewersdorf at The Jackson Laboratory, Bar Harbor, ME., I have been able to exploit a new technology, 4Pi microscopy, to provide the first images of endogenous nuclear proteins using this method. Results presented in this thesis have added significantly to a more complete understanding of cellular localization Rad51, Rad51C and Xrcc3, and have provided important insights into possible mechanisms of cellular trafficking of Rad51 in response to response to DNA damage. Additionally, we have defined a specific function for Rad51C in its regulation of Rad51 ubiquitination. These findings open several new avenues of investigation for furthering our understanding of the cellular and molecular functions of proteins with critical roles in the maintenance of genome integrity in human cells.

Yersinia pestis, the gram-negative causative agent of plague, is a master of immune evasion. The bacterium possesses a type three secretion system which translocates Yop effector proteins into host immune cells to inhibit a number of immune and cell signaling cascades. Interestingly, this apparatus is not expressed at low temperatures such as those found within the flea vector and is therefore neither in place nor functional when the bacteria are first transmitted into a mammalian host. However, the bacterium is still able to avoid activating the immune system, even very early during infection. When grown at 37°C (human body temperature) Y. pestis produces a tetra-acyl lipid A molecule, which is antagonistic to the human Toll like receptor 4/MD2, the major lipopolysaccharide recognition receptor. Although tetra-acyl lipid A binds this receptor complex, it does not induce signaling, and in fact inhibits the receptors interaction with other stimulatory forms of lipid A. The work undertaken in this thesis seeks to determine if the production of tetra-acyl lipid A by Y. pestis is a key virulence determinant and was a critical factor in the evolution of Y. pestis from its ancestral parent Yersinia pseudotuberculosis. By examining the enzymes involved in the lipid A biosynthesis pathway, it has been determined that Y. pestis lacks LpxL, a key enzyme that adds a secondary acyl chain on to the tetra acyl lipid A molecule. In the absence of this enzyme, Y. pestis cannot produce a TLR4 stimulating form of lipid A, whereas Y. pseudotuberculosis does contain the gene for LpxL and produces a stimulatory hexa acyl lipid A. To determine if the absence of LpxL in Y. pestis is important for virulence, LpxL from E. coli and Y. pseudotuberculosis were introduced into Y. pestis. In both cases the addition of LpxL led to bacterium which produced a hexa-acylated lipid A molecule and TLR4/MD2 stimulatory LPS. To verify the LpxL phenotype, lpxL was deleted from Y. pseudotuberculosis, resulting in bacteria which produce tetra-acylated lipid A and nonstimulatory LPS. Mice challenged with LpxL expressing Y. pestis were found to be completely resistant to infection. This profound attenuation in virulence is TLR4 dependent, as mice deficient for this receptor rapidly succumb to disease. These altered strains of the bacterium also act as vaccines, as mice infected with Y. pestis expressing LpxL then challenged with wild type Y. pestis do not become ill. These data demonstrate that the production of tetra-acyl lipid A is a critical virulence determinant for Y. pestis, and that the loss of LpxL formed a major step in the evolution of Y. pestis from Y. pseudotuberculosis. These bacterial strains were also used as tools to determine the contributions of different innate immune receptors and adaptor molecules to the host response during Y. pestis infection. The use of LpxL expressing Y. pestis allowed identification of the innate immune pathways critical for protection during Y. pestis infection. This model also established that CD14 recognition of rough LPS is critical for protection from Y. pestisexpressing LpxL, and activation of the IL-1 receptor and the induction of IL-1β plays a major role in this infection as well. The lipid A acylation profile of gram negative bacteria can have a direct and profound effect on the pathogenesis of the organism. This work illustrates a previously unknown and critical aspect of Y. pestis pathogenesis, which can be extended to other gram-negative pathogens. The greater detail of the contributions which different host adaptor and receptor molecules make to the overall innate immune signaling pathway will allow a better insight into how gram negative infections progress and how they are counteracted by the immune system. Alterations of the lipid A profile of Y. pestis have important implications for the production of vaccines to Y. pestis and other gram negative pathogens. Taken together, this work describes a novel mechanism for immune evasion by gram negative bacteria with consequences for understanding the immune response and the creation of more effective vaccines, both of which will decrease the danger posed by this virulent pathogen.

Vaccinia virus (VAC) is the prototypical member of the orthopoxvirus genus of the poxvirus family and the virus used for smallpox vaccinations. The following describes the testing of VAC variants designed to have similar immuno-protective profiles with decreased pathogenicity, examines the immune response to VAC after lethal infection in wild type and lupus-prone mice, and describes a method that allows for the enumeration of VAC-specific CD8+ T in naïve and VAC-immune mice. The first part describes work examining VAC Wyeth (VAC-Wy) variants engineered to be less pathogenic in vivo. VAC-Wy variants included genes that code for three immunomodulatory proteins, an interferon-γ (IFNγ) binding protein (B8R), an interleukin 18 (IL-18) binding protein (C12L), and a complement binding protein (C3L, or C21L) or various combinations of the three knockouts, and a triple knockout (VAC-Wy -/-/-) in which all three genes were knocked out of a variant virus. The immunomodulatory effects of other IFNγ binding proteins on VAC-Wy pathogenesis in the mouse were also examined. Virus recombinants where the B8R gene was replaced with a truncated mouse IFNγ receptor gene or a gene that encodes a B8R/IFNγ fusion that allows for dimerization of the secreted IFNγ receptor were studied. As the knockouts and variants were made in the current vaccine VAC-Wy strain, only high dose (1x107 PFU’s) intra nasal (I.N.) infection of mice reliably resulted in detectable virus in the lungs. Further testing revealed that all knockout and variant viruses grew to similar levels after high dose I.N. infections. Protection induced by vaccination with the VAC-Wy variants was studied in comparison to immunizations with the VAC-Wy parental strain. Mice were immunized by tail skin scarification to mimic human immunizations, and this was followed months later by I.N. challenge with 20 LD50’s of VAC-WR. All VAC-Wy recombinants tested, including the VAC-Wy -/-/-, provided similar levels of protection as the parental VAC-Wy strain from a lethal VAC-WR I.N. infection. Mice immunized with the VAC-Wy -/-/- induced similar amounts of neutralizing antibody and similar numbers of CD8+ T cells specific to a subdominant determinant as VAC-Wy. While examining high dose, normally lethal, VAC-WR I.N. infections, a profound splenic CD8+ T cell immune suppression was noted that might have been caused by Fas dependent activation induced cell death (AICD). Using high dose intra-peritoneal (I.P.) and I.N. models of VAC-WR infection, decreased weight loss, decreased virus titers, and increased T cell numbers were found in Fas mutant (B6.MRL-Faslpr/J) mice in comparison to B6 wild type mice on day 6. It would be expected that Fas-deficient CD8+ T cells from B6.MRL-Faslpr/J mice (B6-lpr) would survive a high dose VAC-WR infection better than CD8+ T cells that could express Fas if T cells were being eliminated by Fas-dependent AICD, but co-adoptive transfer experiments using splenocytes from B6-lpr and B6.Cg- IgHaThy-1aGPi-1a/J (IgHa) wild type counterparts found no difference in the numbers or proliferation of donor CD8+ T cells at day 6. As the B6-lpr mice were better protected from VAC-induced weight loss early after lethal VAC-WR infections, it was possible that B6-lpr mice might be protected early in infection. In fact, Fas mutant mice had decreased virus loads in the fat pads, livers, and spleens in comparison to B6 wild type mice at days 2 and 3. In addition to the decreased virus titers, the severe splenic lymphocyte deficiency noted in B6 wild type mice as early as day 2 after high dose I.P. infection was ameliorated in B6-lpr mice. Further experiments demonstrated that uninfected B6-lpr mice had increased numbers of memory phenotype (CD44+) CD4+, CD8+ and γδ+ T cells, with an increased number of γδ+ T cells and NK cells in splenic lymphocytes in comparison to wild type B6 mice. Uninfected B6-lpr mice also had increased numbers of IFNγ+ CD8+ T cells after polyclonal stimulation with an antibody against CD3ε. In lymphocyte depletion experiments performed at day 3, antibody depletion of CD4, CD8, or NK or treatment with an antibody that was specific to the γδ+ TCR did not significantly alter virus loads in B6-lpr mice. In co-adoptive transfer experiments, splenocytes from wild type or B6-lpr mice survived high dose VAC-WR challenge similarly suggesting that B6- lpr splenocytes were not intrinsically better protected from lymphocyte depletion by lack of the Fas protein. On day 2 after high dose I.P. VAC-WR infection, B6- lpr mice had increased numbers of IFNγ+ NK cells, IFNγ+ CD8+ T cells, and IFNγ+ CD4+ T cells. B6-lpr and B6 mice treated with an antibody against IFNγ had significantly increased virus titers in the spleens and livers. Interestingly, there was no significant difference in liver or spleen virus titers when comparing anti- IFNγ antibody treated B6 mice or anti-IFNγ antibody treated B6-lpr mice. These results suggest that multiple leukocyte populations co-operatively or redundantly provide B6-lpr mice with increased protection from high dose VAC-WR infections through increased production of IFNγ. The third part of this work describes the enumeration of total numbers of pathogen-specific CD8+ T cells in a mouse through use of an in vivo limiting dilution assay (LDA). The extensive proliferation of virus-specific CD8+ T cells that occurs after virus infection was used to enumerate numbers of virus-specific CD8+ T cells in a naïve mouse. By transferring limiting amounts of carboxyfluorescein succinimidyl ester (CFSE)-labeled Thy1.1+Ly5.2+ heterogeneous CD8+ T cells into Thy1.2+Ly5.1+ hosts, CD8+ T cell precursor frequencies to whole viruses can be calculated. The calculations are based on finding the number of donor CD8+ T cells that results in CFSElo (i.e. proliferated) donor CD8 T cells in 50% of the hosts. Using probit or Reed and Muench 50% endpoint calculations, CD8+ T cell precursor determinations were made for naïve and immune states to a virus challenge. It was found that in naïve B6 mice, 1 in 1444 CD8+ T cells proliferated in response to VAC-WR (~13,852 VAC-WR-specific CD8+ T cells per mouse) and 1 in 2956 proliferated in response to lymphocytic choriomeningitis virus (LCMV) (~6,761 LCMV-specific CD8+ T cells per mouse). In mice immune to VAC-WR, the number of VAC-WR-specific LDA precursors, not surprisingly, dramatically increased to 1 in 13 (~1,538,462 VAC-WR- specific CD8+ T cells per mouse) consistent with estimates of VAC-WR-specific memory T cells. In contrast, precursor numbers to LCMV did not increase in VAC-WR-immune mice (1 in 4562, ~4384 LCMV-specific CD8+ T cells in a VAC-WR-immune mouse) consistent with the fact that VAC-WR provides no heterologous immunity to LCMV. Using H-2Db-restricted LCMV GP33-specific P14 transgenic T cells it was found that, after accounting for take of donor T cells, approximately every T cell transferred underwent a full proliferative expansion in response to an LCMV infection and a high efficiency was also seen in memory populations. This suggests that most antigen-specific T cells will proliferate in response to infections at limiting dilution. These results, which are discussed in comparison to other methods, show that naïve and memory CD8+ T cell precursor frequencies to whole viruses can be remarkably high. In total this work further advances knowledge of the immunity, pathogenesis, and prevention of poxvirus infections. This was accomplished by studying VAC-Wy recombinants as improved vaccines, by examining the mechanisms and cell types important in early protection from high dose poxvirus infections in B6 and B6-lpr mice, and by describing a method to enumerate total numbers of virus-specific CD8+ T cells in a mouse.

DNA damage induces mitotic exit delays through a process that requires the spindle assembly checkpoint (SAC), which blocks the metaphase to anaphase transition in the presence of unaligned chromosomes. Using time-lapse confocal microscopy in syncytial Drosophila embryos, we show that DNA damage leads to arrest during prometaphase and anaphase. In addition, functional GFP fusions to the SAC components MAD2 and Mps1, and the SAC target Cdc20 relocalize to kinetochore through anaphase arrest, and a null mad2mutation blocks damage induced prometaphase and anaphase arrest. We also show that the DNA damage signaling kinase Chk2 is required for damage induced metaphase and anaphase arrest, and that a functional GFP-Chk2 fusion localizes to kinetochores and centrosomes through mitosis. In addition, in the absence of Chk2, we find that DNA damage sufficient to fragment centromere DNA does not delay mitotic exit. We conclude that DNA damage signaling through Chk2 triggers Mad2-dependent delays in mitotic progression, both before or after the metaphase-anaphase transition.

The influx of calcium through N-type calcium channels (N-current) affects a myriad of neuronal functions. These include the triggering of synaptic release of neurotransmitter, adjustment of membrane potential and changes in gene transcription. N-channels are highly modulated proteins, so that N-current is attenuated or potentiated in response to environmental changes. In turn, the modulation of N-current has a direct effect on the downstream events, making the N-channel a focal point in neural signaling, and its modulation a mechanism for short term plasticity. The modulation of N-current by M1 muscarinic receptors (M1Rs) is of particular interest for several reasons. The M1R is instrumental in both cognition and memory formation as indicated by studies using either pharmacological agents aimed at M1Rs or knockout animals lacking M1Rs. Clinically, the M1R is an important target in the treatment of Alzheimer’s disease. Thus, like the N-channel, the M1R is an important element of neural signaling. Moreover, the stimulation of M1Rs affects N-current by through signaling pathways which despite being studied for decades, are not completely understood. For my dissertation I have investigated of M1R signaling on N-current using electrophysiological recordings of N-current from freshly dissociated neurons and from HEK cells expressing N-channels and M1Rs. Asking how one receptor affects one type of calcium channel would seem to be a simple question. However, the answer has many facets. Since M1Rs have multiple downstream effects and N-channels are highly modulated proteins, stimulation of M1Rs initiates several different pathways which modulate N-current. This thesis aims to unravel some of the complexities of the interactions of two vital components of neuronal signaling. Here I present the results of studies elucidating three different actions of M1signaling of N-current modulation. The first study I present here examines the effect of N-channel subunit composition on modulation of N-current. The stimulation of M1Rs in superior cervical ganglion (SCG) neurons elicits a distinct pattern of modulation; inhibiting N-current elicited by strong depolarizations and enhancing current elicited by lesser depolarizations. Thus M1Rs cause two simultaneous modulatory effects on N-current; increasing voltage sensitivity and decreasing overall conductance. I found the expression of the N-channel’s β subunit (CaVβ) determines the observed effect. Specifically when the isoform CaVβ2a is expressed M1 stimulation elicits enhancement without inhibition. Conversely, when CaVβ1b, CaVβ3, or CaVβ4 are expressed M1 stimulation elicits inhibition with out enhancement. These results fit a model in which both the enhancing and inhibiting effects of M1stimulation occur in all channels, but typically inhibition dominates. CaVβ2a blocks inhibition unmasking latent enhancement. Moreover, using mutants and chimeras I found palmitoylation of CaVβ2a at the N-terminus plays a key role in blocking inhibition. My findings predict the expression and localization of different CaVβ isoforms would dramatically alter modulation of N-current and thus may represent a previously unrecognized form of plasticity. The inhibition of N-current by M1Rs is controversial. It has been proposed recently that inhibition is directly attributable to the depletion of phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2] during M1 stimulation. However, in our lab, we have found arachidonic acid (AA) release, which occurs subsequent to PtdIns(4,5)P2 hydrolysis, is both necessary and sufficient to elicit inhibition. Therefore, in a second study, I tested the effect of CaVβ expression on N-current during exogenous AA application and found a pattern of modulation identical to M1R stimulation. Furthermore, I took part in a collaborative project identifying the AA producing enzyme, diacylglycerol lipase (DAGL), to be a necessary component of the inhibitory pathway elicited by M1Rs. These findings provide increased evidence for AA release being a key factor in the M1R stimulated pathway of inhibition. Moreover, these discoveries identify the expression of CaVβ2a and use of specific DAGL inhibitors as a molecular and pharmacological strategy to block inhibition of N-current, respectively. These tools allow the dissection of downstream effects of M1R stimulation, so that other modulatory effects may be observed. The phosphorylation of N-channels by protein kinase C (PKC) blocks inhibition of current brought on by G-protein β and γ subunits (Gβγ) binding directly to the channel. Relief of Gβγ inhibition by other means has been identified as a mechanism of short term plasticity. M1Rs are known to simulate PKC, but a connection between M1Rs and PKC phosphorylation of Nchannels had not been demonstrated. I hypothesized that PKC stimulation may be occluded by other downstream effects of M1Rs. Therefore in a third study, I used a pharmacological approach on SCG neurons to dissect the PKC activating pathway from the other downstream effects of M1 stimulation. I observed modulation of N-current indicating a loss of Gβγ&#; inhibition, thus consistent with PKC phosphorylation of channels. This conclusion reveals another aspect of M1 modulation, which can function as a means of short term plasticity.