DNA double-strand breaks trigger genome-wide sister-chromatid cohesion through Eco1 (Ctf7)

Faithful chromosome segregation and repair of DNA double-strand breaks (DSBs) require cohesin, the protein complex that mediates sister-chromatid cohesion. Cohesion between sister chromatids is thought to be generated only during ongoing DNA replication by an obligate coupling between cohesion establishment factors such as Eco1 (Ctf7) and the replisome. Using budding yeast, we challenge this model by showing that cohesion is generated by an Eco1-dependent but replication-independent mechanism in response to DSBs in G(2)/M. Furthermore, our studies reveal that Eco1 has two functions: a cohesive activity and a conserved acetyltransferase activity, which triggers the generation of cohesion in response to the DSB and the DNA damage checkpoint. Finally, the DSB-induced cohesion is not limited to broken chromosomes but occurs also on unbroken chromosomes, suggesting that the DNA damage checkpoint through Eco1 provides genome-wide protection of chromosome integrity.     

Adrenocorticotropin concentration following administration of thyrotropin-releasing hormone in healthy horses and those with pituitary pars intermedia dysfunction and pituitary gland hyperplasia

OBJECTIVE: To compare the effect of thyrotropin-releasing hormone (TRH) administration on endogenous ACTH concentrations in healthy horses and those with pituitary pars inter-media hyperplasia and compare the test with the dexamethasone suppression test (DST). DESIGN: Prospective case series. ANIMALS: 15 horses with clinical signs of pituitary pars intermedia dysfunction (PPID), 4 horses with equivocal signs of PPID, and 29 horses without signs of PPID. PROCEDURES: ACTH concentrations prior to and after administration of TRH were measured 61 times in 48 horses. Results of the DST (cortisol response) were compared with those of the TRH test in 29 horses. Thirty-three horses (24 with no clinical signs of PPID, 5 with clinical signs of PPID, and 4 with equivocal clinical signs of PPID) were euthanized and necropsied and their pituitary glands evaluated. RESULTS: ACTH concentrations increased in all horses, but magnitude and duration of increase were significantly higher in horses with PPID. Endogenous ACTH concentrations were influenced by season. The ACTH baseline concentrations and response to TRH were not correlated with results of the DST. Results of DST were abnormal only in clinically abnormal horses or those with pars intermedia hyperplasia, but were within reference range in 17 of 26 tests in these horses. CONCLUSIONS AND CLINICAL RELEVANCE: The ACTH response to TRH is a useful test for diagnosis of pituitary gland hyperplasia, particularly in horses in which baseline ACTH concentrations are within reference range. The DST was specific but not sensitive and was inconsistent for individuals, and results often did not agree with the TRH test response.     

Identification of Physiological Traits Underlying Cultivar Differences in Drought Tolerance in Rice and Wheat

Rice is used as a model cereal to study drought response at the molecular level, with the goal of applying results to other cereals. To assess the relevance of results from rice to other species, the kinetics of drought development and plant response of tolerant and susceptible tropical rice ( Oryza sativa L.) and subtropical wheat ( Triticum aestivum L.) cultivars were compared under vegetative and reproductive stage drought in pot experiments. Water was withheld during reproductive stage until plant available soil moisture content was 30 % of field capacity (FC) or leaf wilting was observed, and then reapplied. Rice reached 30 % FC 9 days after withholding water and wheat after 13 days. Before rewatering, both species reached leaf water potentials of −12 bars and similarly low transpiration rates. Stress reduced leaf relative water content, leaf elongation and membrane stability. When water stress was imposed during reproductive stage, pollen fertility was most affected in wheat, while panicle exsertion and anther dehiscence were severely affected in rice. When water stress was imposed during vegetative stage, wheat was less affected to vegetative stage drought than rice. The nature of differences between tolerant and susceptible cultivars was similar for the two species. However, the differential growth habitats and growth rate of plants needs to be considered in these kinds of experiments.