NTR 2.0: a rationally engineered prodrug-converting enzyme with substantially enhanced efficacy for targeted cell ablation

Transgenic expression of bacterial nitroreductase (NTR) enzymes sensitizes eukaryotic cells to prodrugs such as metronidazole (MTZ), enabling selective cell-ablation paradigms that have expanded studies of cell function and regeneration in vertebrates. However, first-generation NTRs required confoundingly toxic prodrug treatments to achieve effective cell ablation, and some cell types have proven resistant. Here we used rational engineering and cross-species screening to develop an NTR variant, NTR 2.0, which exhibits ~100-fold improvement in MTZ-mediated cell-specific ablation efficacy, eliminating the need for near-toxic prodrug treatment regimens. NTR 2.0 therefore enables sustained cell-loss paradigms and ablation of previously resistant cell types. These properties permit enhanced interrogations of cell function, extended challenges to the regenerative capacities of discrete stem cell niches, and novel modeling of chronic degenerative diseases. Accordingly, we have created a series of bipartite transgenic reporter/effector resources to facilitate dissemination of NTR 2.0 to the research community.

Cervical pessary vs vaginal progesterone for prevention of preterm birth in women with twin pregnancy and short cervix: economic analysis following randomized controlled trial

OBJECTIVE

To compare the cost-effectiveness of cervical pessary vs vaginal progesterone to prevent preterm birth and neonatal morbidity in women with twin pregnancy and a short cervix.

METHODS

Between 4 March 2016 and 3 June 2017, we performed this economic analysis following a randomized controlled trial (RCT), performed at My Duc Hospital, Ho Chi Minh City, Vietnam, that compared cervical pessary to vaginal progesterone in women with twin pregnancy and cervical length < 38 mm between 16 and 22 weeks of gestation. We used morbidity-free neonatal survival as a measure of effectiveness. Data on pregnancy outcome, maternal morbidity and neonatal complications were collected prospectively from medical files; additional information was obtained via telephone interviews with the patients. The incremental cost-effectiveness ratio was calculated as the incremental cost required to achieve one extra surviving morbidity-free neonate in the pessary group compared with in the progesterone group. Probabilistic and one-way sensitivity analyses were also performed.

RESULTS

During the study period, we screened 1113 women with twin pregnancy, of whom 300 fulfilled the inclusion criteria of the RCT and gave informed consent to participate. These women were assigned randomly to receive cervical pessary (n = 150) or vaginal progesterone (n = 150), with two women and one woman, respectively, being lost to follow-up. The rate of morbidity-free neonatal survival was significantly higher in the pessary group compared with the progesterone group (n = 241/296 (81.4%) vs 219/298 (73.5%); relative risk, 1.11 (95% CI, 1.02-1.21), P = 0.02). The mean total cost per woman was 3146 € in the pessary group vs 3570 € in the progesterone group (absolute difference, -424 € (95% CI, -842 to -3 €), P = 0.048). The cost per morbidity-free neonate was significantly lower in the pessary group compared with that in the progesterone group (2492 vs 2639 €; absolute difference, -147 € (95% CI, -284 to 10 €), P = 0.035).

CONCLUSION

In women with twin pregnancy and a short cervix, cervical pessary improves significantly the rate of morbidity-free neonatal survival while reducing costs, as compared with vaginal progesterone. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Microsatellite DNA population structure and stock identification of steelhead trout (Oncorhynchus mykiss) in the Nass and Skeena rivers in northern British Columbia

Population structure and the application to genetic stock identification for steelhead (Oncorhynchus mykiss) in the Nass and Skeena Rivers in northern British Columbia was examined using microsatellite markers. Variation at 8 microsatellite loci (Oki200, Omy77, Ots1, Ots3, Ssa85, Ots100, Ots103, and Ots108) was surveyed for approximately 930 steelhead from 7 populations in the Skeena River drainage and 850 steelhead from 10 populations in the Nass River drainage, as well as 1550 steelhead from test fisheries near the mouth of each river. Differentiation among populations within rivers accounted for about 1.9 times the variation observed among years within populations, with differences between drainages less than variation among populations within drainages. In the Nass River, winter-run populations formed a distinct group from the summer-run populations. Winter-run populations were not assessed in the Skeena River watershed. Simulated mixed-stock samples suggested that variation at the 8 microsatellite loci surveyed should provide relatively accurate and precise estimates of stock composition for fishery management applications within drainages. In the Skeena River drainage in 1998, Babine River (27%) and Bulkley drainage populations (31%) comprised the main components of the returns. For the Nass River in 1998 steelhead returning to Bell-Irving River were estimated to have comprised 39% of the fish sampled in the test fishery, with another 27% of the returns estimated to be derived from Cranberry River. The survey of microsatellite variation did not reveal enough differentiation between Nass River and Skeena River populations to be applied confidently in estimation of stock composition in marine fisheries at this time.

The extreme N-terminus of the Caulobacter crescentus surface-layer protein directs export of passenger proteins from the cytoplasm but is not required for secretion of the native protein

The paracrystalline surface layer (S-layer) of Caulobacter crescentus is composed of a single protein (RsaA, 1026 amino acids) that associates noncovalently with the lipopolysaccharide of the outer membrane. Like many other extracellular proteins of Gram-negative bacteria, the S-layer protein is not processed during transport to the cell surface. To study the secretion of RsaA, several N-terminal deletions of the protein were made by modifying the 5'-region of the rsaA gene. This analysis showed that portions of the N-terminus totalling the first 775 N-terminal amino acids (75% of the protein) could be removed from RsaA without abolishing secretion of the remainder of the protein. Although the RsaA N-terminus was not required for secretion, an N-terminal domain consisting of either 34 or 52 RsaA-derived amino acids promoted export of the alkaline phosphatase reporter (PhoA) and a cellulase reporter (delta CenA) from the cytoplasm; using the cellulase reporter, the efficiency of hybrid protein export was estimated at 9%. No enzyme activity was detected in the cell-free culture fluids as the result of expressing any gene fusion, indicating that no hybrid protein was completely secreted from the cell. RsaA:PhoA hybrid proteins were also exported from the E. coli cytoplasm, a bacterium not expected to contain the necessary machinery for the secretion of RsaA. Taken together, these data indicate that the secretion pathway of RsaA relies on a C-terminal secretion signal and that once separated from the context of the native protein, the extreme N-terminus of RsaA can act as an inefficient cryptic export signal that is not used during native RsaA secretion.

A streptavidin-cellulose-binding domain fusion protein that binds biotinylated proteins to cellulose

A fusion protein, Sta-CBDCex, which comprises streptavidin with a cellulose-binding domain (CBDCex) fused to its C terminus, was produced in the cytoplasm of Escherichia coli, where it formed inclusion bodies. Renatured Sta-CBDCex, recovered from the inclusion bodies, adsorbed to Avicel, a microcrystalline cellulose. The cellulose-bound Sta-CBDCex in turn bound biotinylated alkaline phosphatase or biotinylated beta-glucosidase. The immobilized beta-glucosidase remained fully active during 2 weeks of continuous column operation at 50 degrees C.