Enrichment of Cdk1-cyclins at DNA double-strand breaks stimulates Fun30 phosphorylation and DNA end resection

DNA double-strand breaks (DSBs) are one of the most cytotoxic types of DNA lesion challenging genome integrity. The activity of cyclin-dependent kinase Cdk1 is essential for DSB repair by homologous recombination and for DNA damage signaling. Here we identify the Fun30 chromatin remodeler as a new target of Cdk1. Fun30 is phosphorylated by Cdk1 on Serine 28 to stimulate its functions in DNA damage response including resection of DSB ends. Importantly, Cdk1-dependent phosphorylation of Fun30-S28 increases upon DNA damage and requires the recruitment of Fun30 to DSBs, suggesting that phosphorylation increases in situ at the DNA damage. Consistently, we find that Cdk1 and multiple cyclins become highly enriched at DSBs and that the recruitment of Cdk1 and cyclins Clb2 and Clb5 ensures optimal Fun30 phosphorylation and checkpoint activation. We propose that the enrichment of Cdk1-cyclin complexes at DSBs serves as a mechanism for enhanced targeting and modulating of the activity of DNA damage response proteins.     

Effects of burial and storage on germination and seed reserves of 18 tree species in a tropical deciduous forest in Mexico

The changes in germination and seed reserve composition that occur while seeds are stored in the laboratory or buried in the soil are important for understanding the potential and ecological longevity of seeds as well as seed-bank dynamics. Both germination and seed-bank dynamics depend on water availability. We studied 18 tree species, including those with permeable or impermeable seeds, from a tropical deciduous forest in Mexico. We measured seed germination in a growth chamber after (1) dispersal, (2) laboratory storage, (3) seed burial at two field sites and directly in the field, and (4) two rainy seasons. Lipids, nitrogen, and nonstructural carbohydrates were quantified after dispersal and after laboratory or field storage. Sixteen species were viable after three periods of laboratory storage (~3 years). Eleven species were viable after two burial periods in the field (~2 years). Nitrogen concentration decreased after storage and burial in 11 species. Species lipid concentration had a negative relationship with species water content at dispersal and after one burial period, whereas nonstructural carbohydrates showed the opposite trend. Potential and ecological longevities were similar in impermeable seeds. Most of the species studied can form persistent seed banks consisting mainly of species with impermeable seeds that can remain in the soil without degrading their viability. Germination in the field is staggered following natural precipitation pulses as a strategy to stagger seedling recruitment, which may insure against unfavorable conditions.     

Orexin-A up-regulates dopamine D2 receptor and mRNA in the nucleus accumbens Shell

Molecular Biology Reports - Orexins-A (OrxA) and -B (OrxB) neuropeptides are synthesized by a group of neurons located in the lateral hypothalamus and adjacent perifornical area, which send their...     

Comparison of frugivory by howling monkeys (Alouatta palliata) and bats (Artibeus jamaicensis) in the tropical rain forest of Los Tuxtlas,Mexico

Information on the fruit diets of howling monkeys and fruit-eating bats in the tropical rain forest of Los Tuxtlas, Mexico was collected for a year to compare the plant species used. Howling monkeys used 19 plant species whereas bats used 32 plant species as fruit sources. Eleven species were common in the diet of both mammals. A rank analysis at the plant species level showed that the fruit diets of Alouatta and Artibeus were very different. In contrast to bats, howling monkeys displayed a seasonal pattern in fruit consumption. Diet overlap between the two mammals was highest during the monkeys' fruit-eating season. Measures of fruit production in eight trees (four species) indicated marked variations in fruit biomass produced and in length of fruiting from tree to tree and species to species. Peaks in fruit production were typical both at the species and the individual tree levels, demonstrating the very patchy nature of the fruit available to the monkeys and the bats.     

Construction of a model of the human proximal colon

The objective of the present study was to construct a system that re-creates the conditions of fermentation and absorption of the human proximal colon. The model was constructed using a glass tube with an internal dialysis membrane tube. The food substrate was fed into the dialysis membrane three times a day simulating a typical human feeding. The substrate contained 58% carbohydrates, 35% proteins, 3% fiber, 3% starch, and 1% lipids on dry weight base, with 90% moisture. The inoculum was a fecal culture propagated in TSB. The intestinal absorption was simulated using a polyethylene glycol (PEG) solution running continuously outside the dialysis membrane. All microorganisms increased their counts after inoculation, and reached higher counts generally after substrate feed. The most important short chain fatty acids (SCFA: acetic, propionic and butyric acids) were analyzed, and their concentrations inside and outside the membrane were significantly different due to the extraction efficiency of the PEG solution. The greatest production occurred at 48 h. SCFA ratios showed that at the beginning, acetate was the predominant compound, but after 12 h the proportion of butyrate increased and the acetate was decreased. This SCFA production pattern is similar to that reported for the proximal colon in live systems. Continuous operation of the colon model for 48 h was enough to reveal the development of microorganisms and SCFA production. This model reproduced the conditions of the human proximal colon adequately and can be used to study the development of colonic microbiota.