Transgenic Drosophila for Investigating DUX4 and FRG1, Two Genes Associated with Facioscapulohumeral Muscular Dystrophy (FSHD)
Facioscapulohumeral muscular dystrophy (FSHD) is typically an adult onset dominant myopathy. Epigenetic changes in the chromosome 4q35 region linked to both forms of FSHD lead to a relaxation of repression and increased somatic expression of DUX4-fl (DUX4-full length), the pathogenic alternative splicing isoform of the DUX4 gene. DUX4-fl encodes a transcription factor expressed in healthy testis and pluripotent stem cells; however, in FSHD, increased levels of DUX4-fl in myogenic cells lead to aberrant regulation of target genes. DUX4-fl has proven difficult to study in vivo; thus, little is known about its normal and pathogenic roles. The endogenous expression of DUX4-fl in FSHD-derived human muscle and myogenic cells is extremely low, exogenous expression of DUX4-fl in somatic cells rapidly induces cytotoxicity, and, due in part to the lack of conservation beyond primate lineages, viable animal models based on DUX4-fl have been difficult to generate. By contrast, the FRG1 (FSHD region gene 1), which is linked to FSHD, is evolutionarily conserved from invertebrates to humans, and has been studied in several model organisms. FRG1 expression is critical for the development of musculature and vasculature, and overexpression of FRG1 produces a myopathic phenotype, yet the normal and pathological functions of FRG1 are not well understood. Interestingly, DUX4 and FRG1 were recently linked when the latter was identified as a direct transcriptional target of DUX4-FL. To better understand the pathways affected in FSHD by DUX4-fl and FRG1, we generated transgenic lines of Drosophila expressing either gene under control of the UAS/GAL4 binary system. Utilizing these lines, we generated screenable phenotypes recapitulating certain known consequences of DUX4-fl or FRG1 overexpression. These transgenic Drosophila lines provide resources to dissect the pathways affected by DUX4-fl or FRG1 in a genetically tractable organism and may provide insight into both muscle development and pathogenic mechanisms in FSHD.
Versatility of CRISPR/Cas9-based platforms makes them promising tools for the correction of diverse genetic/epigenetic disorders. Here we contrast the use of these genome editing tools in two myopathies with very different molecular origins: Duchenne muscular dystrophy, a monogenetic disease, and facioscapulohumeral muscular dystrophy, an epigenetic disorder with unique therapeutic challenges.
Imaging is an integral part of the multidisciplinary management of cancer. Radiographic techniques are indispensable for proper staging of cancers and evaluation of the response of tumors to treatment. A wide variety of imaging modalities is available to clinicians. This chapter in Cancer Concepts: A Guidebook for the Non-Oncologist will introduce the role of radiology in the diagnosis and treatment of cancer.
The Epithelial Transmembrane Protein PERP Is Required for Inflammatory Responses to S. typhimurium Infection: A Dissertation
Salmonella enterica subtype Typhimurium (S. Typhimurium) is one of many non-typhoidal Salmonella enterica strains responsible for over one million cases of salmonellosis in the United States each year. These Salmonella strains are also a leading cause of diarrheal disease in developing countries. Nontyphoidal salmonellosis induces gastrointestinal distress that is characterized histopathologically by an influx of polymorphonuclear leukocytes (PMNs), the non-specific effects of which lead to tissue damage and contribute to diarrhea.
Prior studies from our lab have demonstrated that the type III secreted bacterial effector SipA is a key regulator of PMN influx during S. Typhimurium infection and that its activity requires processing by caspase-3. Although we established caspase-3 activity is required for the activation of inflammatory pathways during S. Typhimurium infection, the mechanisms by which caspase-3 is activated remain incompletely understood. Most challenging is the fact that SipA is responsible for activating caspase-3, which begs the question of how SipA can activate an enzyme it requires for its own activity.
In the present study, we describe our findings that the eukaryotic tetraspanning membrane protein PERP is required for the S. Typhimuriuminduced influx of PMNs. We further show that S. Typhimurium infection induces PERP accumulation at the apical surface of polarized colonic epithelial cells, and that this accumulation requires SipA. Strikingly, PERP accumulation occurs in the absence of caspase-3 processing of SipA, which is the first time we have shown SipA mediates a cellular event without first requiring caspase-3 processing. Previous work demonstrates that PERP mediates the activation of caspase-3, and we find that PERP is required for Salmonella-induced caspase-3 activation.
Our combined data support a model in which SipA triggers caspase-3 activation via its cellular modulation of PERP. Since SipA can set this pathway in motion without being cleaved by caspase-3, we propose that PERP-mediated caspase-3 activation is required for the activation of SipA, and thus is a key step in the inflammatory response to S. Typhimurium infection. Our findings further our understanding of how SipA induces inflammation during S. Typhimurium infection, and also provide additional insight into how type III secreted effectors manipulate host cells.
Gender Differences in Choice of Procedure and Case Fatality Rate for Elderly Patients with Acute Cholecystitis: A Masters Thesis
Background: Treatment decisions for elderly patients with gallbladder pathology are complex. Little is known about what factors go into treatment decisions in this population. We used Medicare data to examine gender-based differences in the use of cholecystectomy vs. cholecystostomy tube placement in elderly patients with acute cholecystitis.
Methods: We queried a 5% random sample of Medicare data (2009-2011) for patients >65 admitted for acute cholecystitis (by ICD-9 code) who subsequently underwent a cholecystectomy and/or cholecystostomy tube placement. Demographic information (age, race), clinical characteristics (Elixhauser index, presence of biliary pathology), and hospital outcomes (case fatality rate, length of stay, need for ICU care) were compared by gender. A multivariable model was used to examine predictors of cholecystectomy vs. cholecystostomy tube placement.
Results: Of 4063 patients admitted with cholecystitis undergoing the procedures of interest just over half (58%) were women. The majority of patients (93%) underwent cholecystectomy. Compared to women, men were younger (average age 76 vs. 78, p value < 0.01) and had few comorbidities (average Elixhauser 1.2 vs. 1.4 p value < 0.01). Case fatality rate was similar between men (2.5%) and women (2.4% p value 0.48). A higher percentage of men spent time in the ICU (36%) compared to women (31% p value < 0.01). On multivariable analysis men were 30% less likely to undergo cholecystectomy (OR 0.69, 95% CI 0.53-0.91).
Conclusion: Elderly men are less likely than elderly women to undergo cholecystectomy for acute cholecystitis despite being younger with less co morbidity and are more likely to spend time in the ICU. More research is needed to determine whether a difference in treatment is contributing to the higher rate of ICU utilization in elderly men with acute cholecystitis.
PIWI-interacting RNAs (piRNA) are a group of 23–35 nucleotide (nt) short RNAs that protect animal gonads from transposon activities. In Drosophila germ line, piRNAs can be categorized into two different categories— primary and secondary piRNAs— based on their origins. Primary piRNAs, generated from transcripts of specific genomic regions called piRNA clusters, which are enriched in transposon fragments that are unlikely to retain transposition activity. The transcription and maturation of primary piRNAs from those cluster transcripts are poorly understood. After being produced, a group of primary piRNAs associates Piwi proteins and directs them to repress transposons at the transcriptional level in the nucleus. Other than their direct role in repressing transposons, primary piRNAs can also initiate the production of secondary piRNA. piRNAs with such function are loaded in a second PIWI protein named Aubergine (Aub). Similar to Piwi, Aub is guided by piRNAs to identify its targets through base-pairing. Differently, Aub functions in the cytoplasm by cleaving transposon mRNAs. The 5' cleavage products are not degraded but loaded into the third PIWI protein Argonaute3 (Ago3). It is believed that an unidentified nuclease trims the 3' ends of those cleavage products to 23–29 nt, becoming mature piRNAs remained in Ago3. Such piRNAs whose 5' ends are generated by another PIWI protein are named secondary piRNAs. Intriguingly, secondary piRNAs loaded into Ago3 also cleave transposon mRNA or piRNA cluster transcripts and produce more secondary piRNAs loaded into Aub. This reciprocal feed-forward loop, named the “Ping-Pong cycle”, amplified piRNA abundance.
By dissecting and analyzing data from large-scale deep sequencing of piRNAs and transposon transcripts, my dissertation research elucidates the biogenesis of germline piRNAs in Drosophila.
How primary piRNAs are processed into mature piRNAs remains enigmatic. I discover that primary piRNA signal on the genome display a fixed periodicity of ~26 nt. Such phasing depends on Zucchini, Armitage and some other primary piRNA pathway components. Further analysis suggests that secondary piRNAs bound to Ago3 can initiate phased primary piRNA production from cleaved transposon RNAs. The first ~26 nt becomes a secondary piRNA that bind Aub while the subsequent piRNAs bind Piwi, allowing piRNAs to spread beyond the site of RNA cleavage. This discovery adds sequence diversity to the piRNA pool, allowing adaptation to changes in transposon sequence. We further find that most Piwi-associated piRNAs are generated from the cleavage products of Ago3, instead of being processed from piRNA cluster transcripts as the previous model suggests. The cardinal function of Ago3 is to produce antisense piRNAs that direct transcriptional silencing by Piwi, rather to make piRNAs that guide post-transcriptional silencing by Aub. Although Ago3 slicing is required to efficiently trigger phased piRNA production, an alternative, slicing-independent pathway suffices to generate Piwi-bound piRNAs that repress transcription of a subset of transposon families. The alternative pathway may help flies silence newly acquired transposons for which they lack extensively complementary piRNAs.
The Ping-Pong model depicts that first ten nucleotides of Aub-bound piRNAs are complementary to the first ten nt of Ago3-bound piRNAs. Supporting this view, piRNAs bound to Aub typically begin with Uridine (1U), while piRNAs bound to Ago3 often have adenine at position 10 (10A). Furthermore, the majority of Ping-Pong piRNAs form this 1U:10A pair. The Ping-Pong model proposes that the 10A is a consequence of 1U. By statistically quantifying those target piRNAs not paired to g1U, we discover that 10A is not directly caused by 1U. Instead, fly Aub as well as its homologs, Siwi in silkmoth and MILI in mice, have an intrinsic preference for adenine at the t1 position of their target RNAs. On the other hand, this t1A (and g10A after loading) piRNA directly give rise to 1U piRNA in the next Ping-Pong cycle, maximizing the affinity between piRNAs and PIWI proteins.
Single-Molecule Imaging Reveals that Argonaute Re-Shapes the Properties of its Nucleic Acid Guides: A Dissertation
Small RNA silencing pathways regulate development, viral defense, and genomic integrity in all kingdoms of life. An Argonaute (Ago) protein, guided by a tightly bound, small RNA or DNA, lies at the core of these pathways. Argonaute uses its small RNA or DNA to find its target sequences, which it either cleaves or stably binds, acting as a binding scaffold for other proteins. We used Co-localization Single-Molecule Spectroscopy (CoSMoS) to analyze target binding and cleavage by Ago and its guide. We find that both eukaryotic and prokaryotic Argonaute proteins re-shape the fundamental properties of RNA:RNA, RNA:DNA, and DNA:DNA hybridization: a small RNA or DNA bound to Argonaute as a guide no longer follows the well-established rules by which oligonucleotides find, bind, and dissociate from complementary nucleic acid sequences. Counter to the rules of nucleic acid hybridization alone, we find that mouse AGO2 and its guide bind to microRNA targets 17,000 times tighter than the guide without Argonaute. Moreover, AGO2 can distinguish between microRNA-like targets that make seven base pairs with the guide and the products of cleavage, which bind via nine base pairs: AGO2 leaves the cleavage products faster, even though they pair more extensively.
This thesis presents a detailed kinetic interrogation of microRNA and RNA interference pathways. We discovered sub-domains within the previously defined functional domains created by Argonaute and its bound DNA or RNA guide. These sub-domains have features that no longer conform to the well-established properties of unbound oligonucleotides. It is by re-writing the rules for nucleic acid hybridization that Argonautes allow oligonucleotides to serve as specificity determinants with thermodynamic and kinetic properties more typical of RNA-binding proteins than that of RNA or DNA. Taken altogether, these studies further our understanding about the biology of small RNA silencing pathways and may serve to guide future work related to all RNA-guided endonucleases.
Hepatitis C Virus: Structural Insights into Protease Inhibitor Efficacy and Drug Resistance: A Dissertation
The Hepatitis C Virus (HCV) is a global health problem as it afflicts an estimated 170 million people worldwide and is the major cause of viral hepatitis, cirrhosis and liver cancer. HCV is a rapidly evolving virus, with 6 major genotypes and multiple subtypes. Over the past 20 years, HCV therapeutic efforts have focused on identifying the best-in-class direct acting antiviral (DAA) targeting crucial components of the viral lifecycle, The NS3/4A protease is responsible for processing the viral polyprotein, a crucial step in viral maturation, and for cleaving host factors involved in activating immunity. Thus targeting the NS3/4A constitutes a dual strategy of restoring the immune response and halting viral maturation. This high priority target has 4 FDA approved inhibitors as well as several others in clinical development. Unfortunately, the heterogeneity of the virus causes seriously therapeutic challenges, particularly the NS3/4A protease inhibitors (PIs), which suffer from both the rapid emergence of drug resistant mutants as well as a lack of pan-genotypic activity.
My thesis research focused on filling two critical gaps in our structural understanding of inhibitor binding modes. The first gap in knowledge is the molecular basis by which macrocyclization of PIs improves antiviral activity. Macrocycles are hydrophobic chains used to link neighboring chemical moieties within an inhibitor and create a structurally pre-organized ligand. In HCV PIs, macrocycle come in two forms: a P1 - P3 and P2 - P4 strategy. I investigated the structural and thermodynamic basis of the role of macrocyclization in reducing resistance susceptibility. For a rigorous comparison, we designed and synthesized both a P1 - P3 and a linear analog of grazoprevir, a P2 - P4 inhibitor. I found that, while the P2 - P4 strategy is more favorable for achieving potency, it does not allow the inhibitor sufficient flexibility to accommodate resistance mutations. On the other hand, the P1 - P3 strategy strikes a better balance between potency and resistance barrier.
The second gap my thesis addresses is elucidating the structural basis by which highly potent protease inhibitors function in genotype 1 but not in genotype 3, despite having an 87% sequence similarity. After mapping the amino acids responsible for this differential efficacy in genotypes 1 and 3, I engineered a 1a3a chimeric protease for crystallographic studies. My structural characterization of three PIs in complex with both the 1a3a and genotype 1 protease revealed that the loss of inhibitor efficacy in the 1a3a and GT-3 proteases is a consequence of disrupted electrostatic interactions between amino acids 168 and 155, which is critical for potent binding of quinoline and isoindoline based PIs. Here, I have revealed details of molecular and structural basis for the lack of PI efficacy against GT-3, which are needed for design of pan-genotypic inhibitors.
Diet Quality and Evening Snacking in Relation to Sleep Duration and Quality among Women with Young Children: A Dissertation
Background: Mothers’ diets impact their health and the health of their children, but diet quality is suboptimal among women with young children. Evening snacking among women with young children, especially consumption of high-calorie, high-carbohydrate snacks, may impact overall diet quality and glucose metabolism. Short sleep duration and poor sleep quality may be potential risk factors. We examined whether sleep duration and poor sleep quality were associated with diet quality and evening snacking among women with young children.
Methods: Data were from the National Health and Nutrition Examination Survey (NHANES) 2005-2012, nationally representative cross-sectional surveys of noninstitutionalized U.S. population. Eligible participants were non-pregnant women aged 20-44 years within 5 years of childbirth who completed two 24-hour dietary recalls and completed questions on sleep duration and quality.
Results: Among US women with young children, sleep duration was not associated with diet quality. However, overall sleep quality was associated with poorer diet quality. Short sleep duration was not associated with the consumption of neither evening snacks, nor energy intake from or nutrient consumption of evening snacks.
Conclusion: The findings of this dissertation provide information useful for informing the direction of future research of dietary quality and eating behaviors of U.S. women with young children. Studies are needed to explore whether improvement in sleep quality may improve diet quality among women with young children, which has the potential to improve both maternal and children’s health. Research may be better focused on identifying other psychosocial and behavioral risk factors for unhealthy dietary behaviors among US women with young children.