Multilevel interrogation of H3.3 reveals a primordial role in transcription regulation.

BACKGROUND: Eukaryotic cells can rapidly adjust their transcriptional profile in response to molecular needs. Such dynamic regulation is, in part, achieved through epigenetic modifications and selective incorporation of histone variants into chromatin. H3.3 is the ancestral H3 variant with key roles in regulating chromatin states and transcription. Although H3.3 has been well studied in metazoans, information regarding the assembly of H3.3 onto chromatin and its possible role in transcription regulation remain poorly documented outside of Opisthokonts. RESULTS: We used the nuclear dimorphic ciliate protozoan, Tetrahymena thermophila, to investigate the dynamics of H3 variant function in evolutionarily divergent eukaryotes. Functional proteomics and immunofluorescence analyses of H3.1 and H3.3 revealed a highly conserved role for Nrp1 and Asf1 histone chaperones in nuclear influx of histones. Cac2, a putative subunit of H3.1 deposition complex CAF1, is not required for growth, whereas the expression of the putative ortholog of the H3.3-specific chaperone Hir1 is essential in Tetrahymena. Our results indicate that Cac2 and Hir1 have distinct localization patterns during different stages of the Tetrahymena life cycle and suggest that Cac2 might be dispensable for chromatin assembly. ChIP-seq experiments in growing Tetrahymena show H3.3 enrichment over the promoters, gene bodies, and transcription termination sites of highly transcribed genes. H3.3 knockout followed by RNA-seq reveals large-scale transcriptional alterations in functionally important genes. CONCLUSION: Our results provide an evolutionary perspective on H3.3's conserved role in maintaining the transcriptional landscape of cells and on the emergence of specialized chromatin assembly pathways.

The Presence of Diabetes and Higher HbA1c Are Independently Associated With Adverse Outcomes After Surgery.

OBJECTIVE: Limited studies have examined the association between diabetes and HbA1c with postoperative outcomes. We investigated the association of diabetes, defined categorically, and the association of HbA1c as a continuous measure, with postoperative outcomes. RESEARCH DESIGN AND METHODS: In this prospective, observational study, we measured the HbA1c of surgical inpatients age ≥54 years at a tertiary hospital between May 2013 and January 2016. Patients were diagnosed with diabetes if they had preexisting diabetes or an HbA1c ≥6.5% (48 mmol/mol) or with prediabetes if they had an HbA1c between 5.7 and 6.4% (39 and 48 mmol/mol). Patients with an HbA1c <5.7% (39 mmol/mol) were categorized as having normoglycemia. Baseline demographic and clinical data were obtained from hospital records, and patients were followed for 6 months. Random-effects logistic and negative binomial regression models were used for analysis, treating surgical units as random effects. We undertook classification and regression tree (CART) analysis to design a 6-month mortality risk model. RESULTS: Of 7,565 inpatients, 30% had diabetes, and 37% had prediabetes. After adjusting for age, Charlson comorbidity index (excluding diabetes and age), estimated glomerular filtration rate, and length of surgery, diabetes was associated with increased 6-month mortality (adjusted odds ratio [aOR] 1.29 [95% CI 1.05-1.58]; P = 0.014), major complications (1.32 [1.14-1.52]; P < 0.001), intensive care unit (ICU) admission (1.50 [1.28-1.75]; P < 0.001), mechanical ventilation (1.67 [1.32-2.10]; P < 0.001), and hospital length of stay (LOS) (adjusted incidence rate ratio [aIRR] 1.08 [95% CI 1.04-1.12]; P < 0.001). Each percentage increase in HbA1c was associated with increased major complications (aOR 1.07 [1.01-1.14]; P = 0.030), ICU admission (aOR 1.14 [1.07-1.21]; P < 0.001), and hospital LOS (aIRR 1.05 [1.03-1.06]; P < 0.001). CART analysis confirmed a higher risk of 6-month mortality with diabetes in conjunction with other risk factors. CONCLUSIONS: Almost one-third of surgical inpatients age ≥54 years had diabetes. Diabetes and higher HbA1c were independently associated with a higher risk of adverse outcomes after surgery.