SUMOylation mediates CtIP’s functions in DNA end resection and replication fork protection

Double-strand breaks and stalled replication forks are a significant threat to genomic stability that can lead to chromosomal rearrangements or cell death. The protein CtIP promotes DNA end resection, an early step in homologous recombination repair, and has been found to protect perturbed forks from excessive nucleolytic degradation. However, it remains unknown how CtIP’s function in fork protection is regulated. Here, we show that CtIP recruitment to sites of DNA damage and replication stress is impaired upon global inhibition of SUMOylation. We demonstrate that CtIP is a target for modification by SUMO-2 and that this occurs constitutively during S phase. The modification is dependent on the activities of cyclin-dependent kinases and the PI-3-kinase-related kinase ATR on CtIP’s carboxyl-terminal region, an interaction with the replication factor PCNA, and the E3 SUMO ligase PIAS4. We also identify residue K578 as a key residue that contributes to CtIP SUMOylation. Functionally, a CtIP mutant where K578 is substituted with a non-SUMOylatable arginine residue is defective in promoting DNA end resection, homologous recombination, and in protecting stalled replication forks from excessive nucleolytic degradation. Our results shed further light on the tightly coordinated regulation of CtIP by SUMOylation in the maintenance of genome stability.     

Obesity,End‐stage Renal Disease,and Survival in an Elderly Cohort With Cardiovascular Disease

Obesity is highly prevalent in African Americans and is associated with increased risk of End‐Stage Renal Disease (ESRD) and death. It is not known if the effect of obesity is similar among blacks and whites. The aim of this study is to examine racial differences in the association of obesity with ESRD and survival in elderly patients (age >65). Data were obtained for 74,167 Medicare patients with acute myocardial infarction (AMI) between February 1994 and July 1995. BMI was calculated as weight (kg) divided by height (m²). We evaluated the association of BMI class with ESRD incidence and death using multivariable Cox proportional hazards models, testing for race‐BMI interactions. Compared to whites, African Americans had higher BMI (26.9 vs. 26.0, P < 0.0001) and estimated glomerular filtration rate (72.4 ml/min/1.73 m² vs. 66.6 ml/min/1.73 m², P < 0.0001). Crude ESRD rates increased with increasing obesity among whites but not among blacks. However, after adjusting for age, sex, and other comorbidities, obesity was not associated with increased ESRD rate among blacks or whites and the interaction between race and BMI was not significant. Furthermore, for both races, patients classified as overweight, class 1 obese, or class 2 obese had similar, significantly better survival abilities compared to normal weight patients and the race BMI interaction was not significant. In conclusion, obesity does not increase risk of ESRD among black or white elderly subjects with cardiovascular disease (CVD). However, both obese blacks and whites, in this population, experience a survival benefit. Further studies need to explore this obesity paradox.     

Model-building with interpolated temporal data

Ecological data can be difficult to collect, and as a result, some important temporal ecological datasets contain irregularly sampled data. Since many temporal modelling techniques require regularly spaced data, one common approach is to linearly interpolate the data, and build a model from the interpolated data. However, this process introduces an unquantified risk that the data is over-fitted to the interpolated (and hence more typical) instances. Using one such irregularly-sampled dataset, the Lake Kasumigaura algal dataset, we compare models built on the original sample data, and on the interpolated data, to evaluate the risk of mis-fitting based on the interpolated data.     

MRE11-RAD50-NBS1 Complex Is Sufficient to Promote Transcription by RNA Polymerase II at Double-Strand Breaks by Melting DNA Ends

1. Download : Download high-res image (188KB)
2. Download : Download full-size image

     

Community structure and composition of microfaunal egg bank assemblages in riverine and floodplain sediments

Dormancy may be an important aspect influencing the ecology of riverine microfauna, yet fundamental knowledge concerning riverine egg bank communities is still scant compared with that for communities in floodplain habitats. We investigated the microfaunal egg bank communities in slackwater habitats of an Australian floodplain river, and compared them with the communities occurring in nearby floodplain wetlands. This was achieved by taking replicate sediment cores from paired examples of each habitat and later incubating the resting stages within these sediment cores. Results from the study indicated that the egg bank communities in each habitat differed in both composition and structure, with only 12 of the 31 taxa recorded being common to both habitat types. This suggests that in addition to supporting microfaunal persistence in the main channel, riverine egg bank communities represent an important source of microfaunal diversity together with floodplain egg bank communities in river–floodplain systems.     

Culture of human neoplastic gastrointestinal smooth muscle cells

Summary Due to limited growth potential of primary cultures and the absence of continuous lines of healthy enteric smooth muscle, we have studied the culture behavior of neoplastic gastrointestinal smooth muscle cells. Forty-six human enteric smooth muscle neoplasms (leiomyomas and leiomyosarcomas) were studied while fresh and/or after culture in vitro and growth in vivo in athymic nude mice, with assessments made of morphology, growth characteristics, and biochemical markers of differentiation. The state of differentiation of the tumors varied, with well-differentiated tumors tending to express binding sites for the gastrointestinal hormone cholecystokinin, whereas less well-differentiated tumors did not. Poorly differentiated tumors were the easiest to establish in culture in vitro and to grow in vivo in nude mice. When the cells placed directly into culture proliferated to confluent density, they underwent morphologic differentiation from a spread, fibroblastlike shape to a slender spindle morphology, with these cells possessing fewer biosynthetic organelles and arranging themselves in characteristic “hill and valley” arrays. However, the highly differentiated characteristics of expression of desmin or cholecystokinin-binding sites were not observed in cultured cells. In contrast, cells that had been passaged in nude mice before culture displayed a proliferative phenotype and failed to undergo morphologic differentiation on reaching confluent density. Four human enteric smooth muscle cell lines (documented by chromosomal analysis) originating in stomach, jejunum, ileum, and rectum were established using this strategy. This work was supported by grants DK32878 and DK34988 from the National Institutes of Health, Bethesda, MD.