Posttranslational histone modifications contribute to chromatin-dependent processes such as transcriptional regulation and repair of DNA damage. Catalysis of these modifications is carried out by complexes that function in both targeting activities to specific genes and in regulating genome-wide levels of modifications. One form of histone modification is dynamic and reversible acetylation and deacetylation of lysines. In Saccharomyces cerevisiae, Esa1 is an essential histone acetyltransferase that belongs to the conserved MYST family. Esa1 is the catalytic subunit of two chromatin modifying complexes with key roles in transcriptional regulation and DNA repair. In this thesis, three different genetic suppressors of esa1 were identified and characterized, connecting the diverse nuclear functions of Esa1 with multiple cellular processes. NAB3 encodes an RNA binding protein that processes 3'-ends of non-polyadenylated transcripts. Overexpression of NAB3 suppressed the temperature-sensitivity of an esa1 mutant and its defects in rDNA and telomeric silencing. Nab3 was discovered to function in transcriptional silencing at the rDNA locus, cell cycle progression, and DNA damage repair. These are all processes in which Esa1 participates, providing evidence that RNA processing by Nab3 is functionally linked to acetylation by Esa1. Other genetic studies identified two closely-related histone deacetylases, Rpd3 and Hos2, that coordinate with Esa1 in its different functions. The first of these two studies demonstrates that Esa1 and Rpd3 coordinate acetylation of H4 lysine 12 (H4K12) to promote cell viability. RPD3, when deleted, suppressed mutant phenotypes of esa1 including temperature -sensitivity and silencing defects. In particular, growth rescue of esa1 by rpd3 depended specifically on H4K12 acetylation, defining a crucial yet previously unsuspected role for this residue. Notably, of the two biochemically defined Rpd3 complexes, it was Rpd3L that mediated suppression, providing a new distinction from the smaller Rpd3S complex. In contrast to RPD3, deletion of HOS2 suppressed esa1's sensitivity to DNA damaging agents. Initial characterization thus indicates that Esa1 partners with Hos2, and not Rpd3, in response to DNA damage. The work presented in this thesis applies the powerful tool of genetic suppression to important questions about biological roles for chromatin modifying enzymes

Cognitive science is an archipelago of concepts and models,with cross-pollination between topics of interest often prohib-ited by incompatible approaches. Despite this, behavioral per-formance universally depends on information transmission be-tween brain regions and is limited by physical and biologicalconstraints. These constraints can be formalized as informa-tion theoretic constraints on transmission, which provide nor-mative predictions across a surprising range of cognitive do-mains. To illustrate this, we describe a simple variable-lengthrate coding model built with Poisson processes, Bayesian in-ference, and an entropy-based decision threshold. This modelreplicates features of human task performance and provides aprincipled connection between a high-level normative frame-work and neural rate codes. We thereby integrate several dis-joint ideas in cognitive science by translating plausible con-straints into information theoretic terms. Such efforts to trans-late concepts, paradigms and models into common theoreti-cal languages are essential for synthesizing our rich but frag-mented understanding of cognitive systems.

Acetylation is a dynamic posttranslational modification that contributes to chromatin-regulated processes, including DNA replication, repair, recombination, and gene expression. Acetylation is controlled by complexes containing opposing lysine and histone acetyltransferase (KAT and HAT) and deacetylase (KDAC and HDAC) activities. The essential MYST family Esa1 KAT acetylates core histones and many nonhistone substrates. Phenotypes of esa1 mutants include transcriptional silencing and activation defects, impaired growth at high temperatures, and sensitivity to DNA damage. The KDAC Rpd3 was previously identified as an activity opposing Esa1, as its deletion suppresses growth and silencing defects of esa1 mutants. However, loss of Rpd3 does not suppress esa1 DNA damage sensitivity. In this work, we identified Hos2 as a KDAC counteracting ESA1 in the damage response. Deletion of HOS2 resulted in changes of esa1's transcriptional response upon damage. Further, loss of HOS2 or components of the Set3 complex (Set3C) in which it acts specifically suppressed damage sensitivity and restored esa1 histone H4 acetylation. This rescue was mediated via loss of either Set3C integrity or of its binding to dimethylated histone H3K4. Our results thus add new insight into the interactions of an essential MYST acetyltransferase with diverse deacetylases to respond specifically to environmental and physiological challenges.

Objective

Machine learning techniques have demonstrated superior discrimination compared to conventional statistical approaches in predicting trauma death. The objective of this study is to evaluate whether machine learning algorithms can be used to assess risk and dynamically identify patient-specific modifiable factors critical to patient trajectory for multiple key outcomes after severe injury.

Methods

SuperLearner, an ensemble machine-learning algorithm, was applied to prospective observational cohort data from 1494 critically-injured patients. Over 1000 agnostic predictors were used to generate prediction models from multiple candidate learners for outcomes of interest at serial time points post-injury. Model accuracy was estimated using cross-validation and area under the curve was compared to select among predictors. Clinical variables responsible for driving outcomes were estimated at each time point.

Results

SuperLearner fits demonstrated excellent cross-validated prediction of death (overall AUC 0.94-0.97), multi-organ failure (overall AUC 0.84-0.90), and transfusion (overall AUC 0.87-0.9) across multiple post-injury time points, and good prediction of Acute Respiratory Distress Syndrome (overall AUC 0.84-0.89) and venous thromboembolism (overall AUC 0.73-0.83). Outcomes with inferior data quality included coagulopathic trajectory (AUC 0.48-0.88). Key clinical predictors evolved over the post-injury timecourse and included both anticipated and unexpected variables. Non-random missingness of data was identified as a predictor of multiple outcomes over time.

Conclusions

Machine learning algorithms can be used to generate dynamic prediction after injury while avoiding the risk of over- and under-fitting inherent in ad hoc statistical approaches. SuperLearner prediction after injury demonstrates promise as an adaptable means of helping clinicians integrate voluminous, evolving data on severely-injured patients into real-time, dynamic decision-making support.

Introduction

Despite the rising trend in breast cancer incidence and mortality across Sub-Saharan Africa, there remains a critical knowledge gap about the burden and patterns of breast disease and breast cancer screening practices at the population level. This study aimed to identify socioeconomic factors associated with knowledge and practice of breast self-examination (BSE) as well as assess the prevalence of breast disease symptoms among a mixed urban-rural population of women in the Southwest region of Cameroon.

Methods

We conducted a household-level community-based study in Southwest Cameroon between January and March 2017, using a three-stage cluster sampling framework. We surveyed 1287 households and collected self-reported data on 4208 female subjects, 790 of whom were household representatives. Each household representative provided information on behalf of all female household members about any ongoing breast disease symptoms. Moreover, female household representatives were questioned about their own knowledge and practice of BSE.

Results

Women demonstrated low frequency of knowledge of BSE, as 25% (n=201) of household representatives reported any knowledge of BSE; and among these only 15% (n=30) practiced BSE on a monthly basis. Age (aOR: 1.04), usage of Liquid Petroleum Gas fuel, a marker of higher socioeconomic status (aOR: 1.86), and speaking English as a primary language in the household (aOR: 1.59) were significant predictors of knowledge of BSE. Eleven women reported ongoing breast disease symptoms resulting in an overall prevalence of 2.3 cases of breast disease symptoms per 1000 women.

Conclusions

Socioeconomic disparities in access to health education may be a determinant of knowledge of BSE. Community-based strategies are needed to improve dissemination of breast cancer screening methods, particularly for women who face barriers to accessing care.

Background

Global surgery research efforts have been criticized for failure to transition from problem identification to intervention implementation. We developed a context-appropriate trauma quality improvement (TQI) bundle to ameliorate care gaps at a regional referral hospital in Cameroon. We determined associations between bundle implementation and improvement in trauma resuscitation practices.

Methods

We implemented a TQI bundle consisting of a hospital-specific trauma protocol, staff training, a trauma checklist, provision of essential emergency trauma supplies in the resuscitation area, and monthly quality improvement meetings. We compared trends in target process measures (e.g., frequency and timing of vital sign collection and primary survey interventions) in the six-month period pre- and post-bundle implementation using Wilcoxon rank-sum and Fisher's exact tests.

Results

We compared 246 pre-bundle patients with 203 post-bundle patients. Post-bundle patients experienced a greater proportion of all vital signs collected compared to the pre-intervention cohort (0 % pre-bundle vs. 69 % post-bundle, p < 0.001); specifically, the proportion of respiratory rate (0.8 % pre-bundle vs. 76 % post-bundle, p < 0.001) and temperature (7 % pre-bundle vs. 91 % post-bundle, p < 0.001) vital sign collection significantly increased. The post-bundle cohort had vital signs measured sooner (74 % vital signs measured within 15 min of arrival pre-bundle vs. 90 % post-bundle, p < 0.001) and more frequently per patient (7 % repeated vitals pre-bundle vs 52 % post-bundle, p < 0.001). Key primary survey interventions such as respiratory interventions (1 % pre-bundle vs. 8 % post-bundle, p < 0.001) and cervical collar placement (0 % pre-bundle vs. 7 % post-bundle, p < 0.001) also increased in the post-bundle cohort.

Conclusions

The implementation of a context-appropriate TQI bundle was associated with significant improvements in previously identified trauma care deficits at a single regional hospital. Data-derived interventions targeting frontline capacity at the local level can bridge the gap between identifying care limitations and improvement in resource-limited settings.

Introduction

Extremity injuries are a leading cause of morbidity in low- and middle-income countries (LMICs), often resulting in marked short-term and long-term disabilities. Most of the existing knowledge on these injuries originates from hospital-based studies; however, poor access to health care in LMICs limits these data because of inherent selection bias. This subanalysis of a larger population-level cross-sectional study in the Southwest Region of Cameroon aims to determine patterns of limb injury, treatment-seeking behaviors, and predictors of disability.

Methods

Households were surveyed in 2017 on injuries and subsequent disability sustained over the previous 12 months using a three-stage cluster sampling framework. Subgroups were compared using the chi square, Fisher exact, analysis of variance, Wald, and Wilcoxon rank-sum tests. Logarithmic models were used to identify predictors of disability.

Results

Of 8,065 subjects, 335 persons (4.2%) sustained 363 isolated limb injuries. Over half of the isolated limb injuries (55.7%) were open wounds while 9.6% were fractures. Isolated limb injuries most commonly occurred in younger men and resulted from falls (24.3%) and road traffic injuries (23.5%). High rates of disability were reported, with 39% reporting difficulty with activities of daily living. Compared with individuals with other types of limb injuries, those with fractures were six times more likely to seek a traditional healer first for care (40% versus 6.7%), 5.3 times (95% CI, 1.21 to 23.42) more likely to have any level of disability after adjustment for injury mechanism, and 2.3 times more likely to have difficulty paying for food or rent (54.8% versus 23.7%).

Discussion

Most traumatic injuries sustained in LMICs involve limb injuries and often result in high levels of disability that affect individuals during their most productive years. Improved access to care and injury control measures, such as road safety training and improvements to transportation and trauma response infrastructure, are needed to reduce these injuries.

Injury-related deaths overwhelmingly occur in low and middle-income countries (LMICs). Community-based injury surveillance is essential to accurately capture trauma epidemiology in LMICs, where one-third of injured individuals never present to formal care. However, community-based studies are constrained by the lack of a validated surrogate injury severity metric. The primary objective of this bipartite study was to cross-validate a novel community-based injury severity (CBS) scoring system with previously-validated injury severity metrics using multi-center trauma registry data. A set of targeted questions to ascertain injury severity in non-medical settings-the CBS test-was iteratively developed with Cameroonian physicians and laypeople. The CBS test was first evaluated in the community-setting in a large household-based injury surveillance survey in southwest Cameroon. The CBS test was subsequently incorporated into the Cameroon Trauma Registry, a prospective multi-site national hospital-based trauma registry, and cross-validated in the hospital setting using objective injury metrics in patients presenting to four trauma hospitals. Among 8065 surveyed household members with 503 injury events, individuals with CBS indicators (CBS+) were more likely to report ongoing disability after injury compared to CBS- individuals (OR 1.9, p = 0.004), suggesting the CBS test is a promising injury severity proxy. In 9575 injured patients presenting for formal evaluation, the CBS test strongly predicted death in patients after controlling for age, sex, socioeconomic status, and injury type (OR 30.26, p<0.0001). Compared to established injury severity scoring systems, the CBS test comparably predicts mortality (AUC: 0.8029), but is more feasible to calculate in both the community and clinical contexts. The CBS test is a simple, valid surrogate metric of injury severity that can be deployed widely in community-based surveys to improve estimates of injury severity in under-resourced settings.

Introduction

Mortality prediction aids clinical decision-making and is necessary for trauma quality improvement initiatives. Conventional injury severity scores are often not feasible in low-resource settings. We hypothesize that clinician assessment will be more feasible and have comparable discrimination of mortality compared to conventional scores in low and middle-income countries (LMICs).

Methods

Between 2017 and 2019, injury data were collected from all injured patients as part of a prospective, four-hospital trauma registry in Cameroon. Clinicians used physical exam at presentation to assign a highest estimated abbreviated injury scale (HEAIS) for each patient. Discrimination of hospital mortality was evaluated using receiver operating characteristic curves. Discrimination of HEAIS was compared with conventional scores. Data missingness for each score was reported.

Results

Of 9,635 presenting with injuries, there were 206 in-hospital deaths (2.2%). Compared to 97.5% of patients with HEAIS scores, only 33.2% had sufficient data to calculate a Revised Trauma Score (RTS) and 24.8% had data to calculate a Kampala Trauma Score (KTS). Data from 2,328 patients with all scores was used to compare models. Although statistically inferior to the prediction generated by RTS (AUC 0.92-0.98) and KTS (AUC 0.93-0.99), HEAIS provided excellent overall discrimination of mortality (AUC 0.84-0.92). Among 9,269 patients with HEAIS scores was strongly predictive of mortality (AUC 0.93-0.96).

Conclusion

Clinical assessment of injury severity using HEAIS strongly predicts hospital mortality and far exceeds conventional scores in feasibility. In contexts where traditional scoring systems are not feasible, utilization of HEAIS could facilitate improved data quality and expand access to quality improvement programming.

Background

Trauma-induced coagulopathy can present as abnormalities in a conventional or viscoelastic coagulation assay or both. We hypothesized that patients with discordant coagulopathies reflect different clinical phenotypes.

Methods

Blood samples were collected prospectively from critically injured patients upon arrival at two urban Level I trauma centers. International normalized ratio (INR), partial thromboplastin time (PTT), thromboelastography (TEG), and coagulation factors were assayed.

Results

278 patients (median ISS 17, mortality 26%) were coagulopathic: 20% with isolated abnormal INR and/or PTT (CONVENTIONAL), 49% with isolated abnormal TEG (VISCOELASTIC), and 31% with abnormal INR/PTT and TEG (BOTH). Compared with VISCOELASTIC, CONVENTIONAL and BOTH had higher ISS, lower GCS, larger base deficit, and decreased factor activities (all p < 0.017). They received more blood products and had more ICU/ventilation days (all p < 0.017). Mortality was higher in CONVENTIONAL (40%) and BOTH (49%) than VISCOELASTIC (6%, p < 0.017).

Conclusions

Although TEG-guided resuscitation improves survival after injury, INR and PTT identify coagulopathic patients with highest mortality regardless of TEG and likely represent distinct mechanisms independent of biochemical clot strength.