SRSF3 shapes the structure of miR-17-92 cluster RNA and promotes selective processing of miR-17 and miR-20a.

MicroRNA (miRNA) biogenesis is tightly regulated to maintain distinct miRNA expression patterns. Almost half of mammalian miRNAs are generated from miRNA clusters, but this process is not well understood. We show here that Serine-arginine rich splicing factor 3 (SRSF3) controls the processing of miR-17-92 cluster miRNAs in pluripotent and cancer cells. SRSF3 binding to multiple CNNC motifs downstream of Drosha cleavage sites within miR-17-92 is required for the efficient processing of the cluster. SRSF3 depletion specifically compromises the processing of two paralog miRNAs, miR-17 and miR-20a. In addition to SRSF3 binding to the CNNC sites, the SRSF3 RS-domain is essential for miR-17-92 processing. SHAPE-MaP probing demonstrates that SRSF3 binding disrupts local and distant base pairing, resulting in global changes in miR-17-92 RNA structure. Our data suggest a model where SRSF3 binding, and potentially its RS-domain interactions, may facilitate an RNA structure that promotes miR-17-92 processing. SRSF3-mediated increase in miR-17/20a levels inhibits the cell cycle inhibitor p21, promoting self-renewal in normal and cancer cells. The SRSF3-miR-17-92-p21 pathway operates in colorectal cancer, linking SRSF3-mediated pri-miRNA processing and cancer pathogenesis.

Genetic epidemiology of beta-thalassemia in the Maldives: 23 years of a beta-thalassemia screening program.

The Maldives is an archipelago of 407,660 people according to population census of 2014, made up of 20 atolls, which has one of the highest prevalence of ß-thalassemia worldwide. However, there is a dearth of studies related to ß-thalassemia in the Maldives; therefore, in this study, we aimed to investigate the genetic epidemiology of ß-thalassemia in Maldives. Blood samples were collected from 110,504 participants (1992-2015). Hemoglobin and RBC indices were measured on automated hematology analyzers. The quantitation of hemoglobin, HbA2, Hb F, and other abnormal Hb variants were assessed by HPLC. Molecular analysis was performed for the most common mutations in Southeast Asia for only 874 individuals either heterozygous or homozygous for these mutations using reverse dot blot hybridization. We screened 110,504 individuals for ß-thalassemia between 1992 and 2015, which is ~ 30% of the entire population. The ß-thalassemia carrier frequency was estimated to be 16.2%. Molecular diagnosis of 874 ß-thalassemia carriers/major was performed for the most common seven mutations in Southeast Asia; of these, 139 patients were diagnosed as ß-thalassemia major. This analysis showed that the most common mutations were IVS1 + 5G > C, (678; 77.6%), followed by the CD 30 (136; 15.6%). The least frequent mutation was FS8/9, (1, 0.001%), followed by IVS1 + 1G > T and CD15 (2; 0.2%). The frequency of ß-thalassemia varies significantly among the 20 different atolls in Maldives. This study is expected to improve genetic counseling, creating awareness, enhance premarital screening, and customize the prevention and treatment strategies based on the needs of each atoll.

An antirepressor, SrpR, is involved in transcriptional regulation of the SrpABC solvent tolerance efflux pump of Pseudomonas putida S12.

Organic compounds exhibit various levels of toxicity toward living organisms based upon their ability to insert into biological membranes and disrupt normal membrane function. The primary mechanism responsible for organic solvent tolerance in many bacteria is energy-dependent extrusion via efflux pumps. One such bacterial strain, Pseudomonas putida S12, is known for its high tolerance to organic solvents as provided through the SrpABC resistance-nodulation-cell division (RND) family efflux pump. To determine how two putative regulatory proteins (SrpR and SrpS, encoded directly upstream of the SrpABC structural genes) influence SrpABC efflux pump expression, we conducted transcriptional analysis, ß-galactosidase fusion experiments, electrophoretic mobility shift assays, and pulldown analysis. Together, the results of these experiments suggest that expression of the srpABC operon can be derepressed by two distinct but complementary mechanisms: direct inhibition of the SrpS repressor by organic solvents and binding of SrpS by its antirepressor SrpR.

Isolation and characterization of novel organic solvent-tolerant bacteria.

Some organic solvents are extremely toxic to living organisms by virtue of their ability to partition into and disrupt the normal functioning of biological membranes. In recent years, several bacteria have been discovered that are more tolerant to these toxic solvents than most microorganisms. Using enrichment procedures, we have isolated new organic solvent-tolerant bacteria from both hyrdocarbon-contaminated and pristine soil samples. These organisms were characterized by several different experimental procedures including description of their cellular physiology, 16S rDNA homology, organic solvent tolerance range, and survival after solvent exposure. The results indicate that gram-positive bacteria can be isolated from the environment that are as tolerant to toxic organic solvents, if not more so, than the most organic solvent-tolerant gram-negative bacteria.