Insights into Spt6: a histone chaperone that functions in transcription, DNA replication, and genome stability.

Transcription elongation requires elaborate coordination between the transcriptional machinery and chromatin regulatory factors to successfully produce RNA while preserving the epigenetic landscape. Recent structural and genomic studies have highlighted that suppressor of Ty 6 (Spt6), a conserved histone chaperone and transcription elongation factor, sits at the crux of the transcription elongation process. Other recent studies have revealed that Spt6 also promotes DNA replication and genome integrity. Here, we review recent studies of Spt6 that have provided new insights into the mechanisms by which Spt6 controls transcription and have revealed the breadth of Spt6 functions in eukaryotic cells.

Distribution of Invasive Aedes Mosquitoes in West-Central Illinois, 2014-18: Record Updates for Aedes japonicus and Ae. albopictus.

A comprehensive surveillance of Aedes mosquitoes in west-central Illinois has not been conducted in recent years, resulting in incomplete distribution records for several Illinois counties. As of 2014, out of 102 Illinois counties, active populations of Ae. japonicus had been confirmed in 15 counties, and Ae. albopictus confirmed in 34 counties. The Miller laboratory at Western Illinois University (WIU) began the WIU Vector Biology Initiative (WIU-VBI) in 2014 to address the lack of mosquito surveillance in west-central Illinois. Through this effort, the presence of Ae. japonicus was confirmed for the 1st time in Fulton, Hancock, and Schuyler counties, IL, from 2014 to 2018. Actively breeding populations were confirmed in Cass, Fulton, McDonough, and Schuyler counties, IL. Additionally, Ae. albopictus was observed for the 1st time in Cass, Fulton, Hancock, McDonough, and Schuyler counties, IL, in 2016 and 2017, with active breeding populations in Cass and McDonough counties, IL.

The conserved histone chaperone Spt6 is strongly required for DNA replication and genome stability.

Histone chaperones are an important class of proteins that regulate chromatin accessibility for DNA-templated processes. Spt6 is a conserved histone chaperone and key regulator of transcription and chromatin structure. However, its functions outside of these roles have been little explored. In this work, we demonstrate a requirement for S. cerevisiae Spt6 in DNA replication and, more broadly, as a regulator of genome stability. Depletion or mutation of Spt6 impairs DNA replication in vivo. Additionally, spt6 mutants are sensitive to DNA replication stress-inducing agents. Interestingly, this sensitivity is independent of the association of Spt6 with RNA polymerase II (RNAPII), suggesting that spt6 mutants have a transcription-independent impairment of DNA replication. Specifically, genomic studies reveal that spt6 mutants have decreased loading of the MCM replicative helicase at replication origins, suggesting that Spt6 promotes origin licensing. Our results identify Spt6 as a regulator of genome stability, at least in part through a role in DNA replication.

Identification of a Trm732 Motif Required for 2'-O-methylation of the tRNA Anticodon Loop by Trm7.

Posttranscriptional tRNA modifications are essential for proper gene expression, and defects in the enzymes that perform tRNA modifications are associated with numerous human disorders. Throughout eukaryotes, 2'-O-methylation of residues 32 and 34 of the anticodon loop of tRNA is important for proper translation, and in humans, a lack of these modifications results in non-syndromic X-linked intellectual disability. In yeast, the methyltransferase Trm7 forms a complex with Trm732 to 2'-O-methylate tRNA residue 32 and with Trm734 to 2'-O-methylate tRNA residue 34. Trm732 and Trm734 are required for the methylation activity of Trm7, but the role of these auxiliary proteins is not clear. Additionally, Trm732 and Trm734 homologs are implicated in biological processes not directly related to translation, suggesting that these proteins may have additional cellular functions. To identify critical amino acids in Trm732, we generated variants and tested their ability to function in yeast cells. We identified a conserved RRSAGLP motif in the conserved DUF2428 domain of Trm732 that is required for tRNA modification activity by both yeast Trm732 and its human homolog, THADA. The identification of Trm732 variants that lack tRNA modification activity will help to determine if other biological functions ascribed to Trm732 and THADA are directly due to tRNA modification or to secondary effects due to other functions of these proteins.

Impact of Venetoclax and Azacitidine in Treatment-Naïve Patients with Acute Myeloid Leukemia and IDH1/2 Mutations.

PURPOSE: To evaluate efficacy and safety of venetoclax + azacitidine among treatment-naïve patients with IDH1/2-mutant (mut) acute myeloid leukemia (AML). PATIENTS AND METHODS: Data were pooled from patients enrolled in a phase III study (NCT02993523) that compared patients treated with venetoclax + azacitidine or placebo + azacitidine and a prior phase Ib study (NCT02203773) where patients were treated with venetoclax + azacitidine. Enrolled patients were ineligible for intensive therapy due to age ≥75 years and/or comorbidities. Patients on venetoclax + azacitidine received venetoclax 400 mg orally (days 1-28) and azacitidine (75 mg/m2; days 1-7/28-day cycle). RESULTS: In the biomarker-evaluable population, IDH1/2mut was detected in 81 (26%) and 28 (22%) patients in the venetoclax + azacitidine and azacitidine groups. Composite complete remission [CRc, complete remission (CR)+CR with incomplete hematologic recovery (CRi)] rates (venetoclax + azacitidine/azacitidine) among patients with IDH1/2mut were 79%/11%, median duration of remission (mDoR) was 29.5/9.5 months, and median overall survival (mOS) was 24.5/6.2 months. CRc rates among patients with IDH1/2 wild-type (WT) were 63%/31%, mDoR 17.5/10.3 months, and mOS 12.3/10.1 months. In patients with IDH1mut, CRc rates (venetoclax + azacitidine/azacitidine) were 66.7%/9.1% and mOS 15.2/2.2 months. In patients with IDH2mut, CRc rates were 86.0%/11.1% and mOS not reached (NR)/13.0 months. Patients with IDH1/2 WT AML treated with venetoclax + azacitidine with poor-risk cytogenetics had inferior outcomes compared with patients with IDH1/2mut, who had superior outcomes regardless of cytogenetic risk (mOS, IDH1/2mut: intermediate-risk, 24.5 months; poor-risk, NR; IDH1/2 WT: intermediate, 19.2 and poor, 7.4 months). There were no unexpected toxicities in the venetoclax + azacitidine group. CONCLUSIONS: Patients with IDH1/2mut who received venetoclax + azacitidine had high response rates, durable remissions, and significant OS; cytogenetic risk did not mitigate the favorable outcomes seen from this regimen for IDH1/2mut. See related commentary by Perl and Vyas, p. 2719.

Impact of FLT3 Mutation on Outcomes after Venetoclax and Azacitidine for Patients with Treatment-Naïve Acute Myeloid Leukemia.

PURPOSE: To evaluate efficacy and safety of venetoclax + azacitidine among treatment-naïve patients with FLT3-mutant acute myeloid leukemia. PATIENTS AND METHODS: Data were pooled from patients enrolled in a phase III study (NCT02993523) that compared patients treated with venetoclax + azacitidine or placebo + azacitidine and a prior phase Ib study (NCT02203773) where patients were treated with venetoclax + azacitidine. Enrolled patients were ineligible for intensive therapy due to age ≥75 years and/or comorbidities. Patients on venetoclax + azacitidine received venetoclax 400 mg orally (days 1-28) and azacitidine (75 mg/m2; days 1-7/28-day cycle). FLT3 mutation was analyzed centrally on pretreatment bone marrow aspirates. RESULTS: In the biomarker evaluable population, FLT3 mutation was detected in 42 (15%) and 22 (19%) patients in the venetoclax + azacitidine and azacitidine groups. Composite complete remission [CRc; complete remission (CR) + CR with incomplete hematologic recovery (CRi)] rates (venetoclax + azacitidine/azacitidine) for FLT3-mutant patients were 67%/36%, median duration of remission (DoR) was 17.3/5.0 months, and median OS was 12.5/8.6 months. The CRc rates among FLT3 wild-type patients were 67%/25%, median DoR 18.4/13.4 months, and median OS 14.7/10.1 months. In patients treated with venetoclax + azacitidine, CRc in patients with FLT3-ITD and FLT3-TKD was 63% and 77% and median OS was 9.9 and 19.2 months, and in comutated FLT3-ITD + NPM1 patients, CRc was 70%, median DoR was not reached, and median OS was 9.1 months. There were no unexpected toxicities in the venetoclax + azacitidine group. CONCLUSIONS: When treated with venetoclax + azacitidine, patients with FLT3 mutations and FLT3 wild-type had similar outcomes. Future analyses in larger patient populations may further define the impact of venetoclax + azacitidine in patients harboring FLT3-ITD. See related commentary by Perl and Vyas, p. 2719.