Chromatin-Associated Proteins HP1 and Mod(mdg4) Modify Y-Linked Regulatory Variation in the Drosophila Testis

Chromatin remodeling is crucial for gene regulation. Remodeling is often mediated through chemical modifications of the DNA template, DNA-associated proteins, and RNA-mediated processes. Y-linked regulatory variation (YRV) refers to the quantitative effects that polymorphic tracts of Y-linked chromatin exert on gene expression of X-linked and autosomal genes. Here we show that naturally occurring polymorphisms in the Drosophila melanogaster Y chromosome contribute disproportionally to gene expression variation in the testis. The variation is dependent on wild-type expression levels of mod(mdg4) as well as Su(var)205; the latter gene codes for heterochromatin protein 1 (HP1) in Drosophila. Testis-specific YRV is abolished in genotypes with heterozygous loss-of-function mutations for mod(mdg4) and Su(var)205 but not in similar experiments with JIL-1. Furthermore, the Y chromosome differentially regulates several ubiquitously expressed genes. The results highlight the requirement for wild-type dosage of Su(var)205 and mod(mdg4) in enabling naturally occurring Y-linked regulatory variation in the testis. The phenotypes that emerge in the context of wild-type levels of the HP1 and Mod(mdg4) proteins might be part of an adaptive response to the environment.     

Sex differences in the rate of fatigue development and recovery

Background

Many musculoskeltal injuries in the workplace have been attributed to the repetitive loading of muscle and soft tissues. It is not disputed that muscular fatigue is a risk factor for musculoskeltal injury, however the disparity between gender with respect to muscular fatigability and rate of recovery is not well understood. Current health and safety guidelines do not account for sex differences in fatiguability and may be predisposing one gender to greater risk. The purpose of this study was to quantify the sex differences in fatigue development and recovery rate of lower and upper body musculature after repeated bouts of sustained isometric contractions.

Methods

Twenty-seven healthy males (n = 12) and females (n = 15) underwent bilateral localized fatigue of either the knee extensors (male: n = 8; female: n = 8), elbow flexors (male: n = 8; female: n = 10), or both muscle groups. The fatigue protocol consisted of ten 30-second sub-maximal isometric contractions. The changes in maximum voluntary contraction (MVC), electrically evoked twitches, and motor unit activation (MUA) were assessed along with the ability to control the sustained contractions (SLP) during the fatigue protocol using a mixed four-factor repeated measures ANOVA (gender × side × muscle × time) design with significance set at p < 0.05.

Results

There was a significant loss of MVC, MUA, and evoked twitch amplitude from pre- to post-fatigue in both the arms and legs. Males had greater relative loss of isometric force, a higher rate of fatigue development, and were less capable of maintaining the fatiguing contractions in the legs when compared to the females.

Conclusion

The nature of the induced fatigue was a combination of central and peripheral fatigue that did not fully recover over a 45-minute period. The results appear to reflect sex differences that are peripheral, and partially support the muscle mass hypothesis for explaining differences in muscular fatigue.

     

Relations among heterotrophic bacteria, chlorophyll-a, total phytoplankton, total zooplankton and physical and chemical features in the Paranoá reservoir, Brasília, Brazil

The plankton community, chlorophyll-a, heterotrophic bacteria and physical and chemical features of the Paranoá Reservoir were studied at monthly intervals at seven stations from March 1988 to March 1989. Thermal structure had a circulation period from May to July and stratification during the other months. The phytoplankton consisted of 76 taxa, was dominated by the cyanophyte Cylindrospermopsis raciborskii and attained concentrations ranging from 7,759,000 up to 98,160,000 org. l^–1. The zooplankton consisted of 36 taxa and was present in densities between 8 and 8,056 org. l^–1. In stations, or seasons with highly eutrophic conditions, there was a decrease in total phytoplankton and an increase in bacteria and total zooplankton. The results had spatial and temporal variations. Spatial variation demonstrated the existence of water quality deterioration at two or three sampling points. Temporal variation showed the influences of water column stability and the dry versus rainy seasons on nutrient concentrations and the planktonic community.     

Cyanobacteria in mangrove ecosystems

Mangroves are subject to the effects of tides and fluctuations in environmental conditions, which may reach extreme conditions. These ecosystems are severely threatened by human activities despite their ecological importance. Although mangroves are characterized by a highly specialized but low plant diversity in comparison to most other tropical ecosystems, they support a diverse microbial community. Adapted microorganisms in soil, water, and on plant surfaces perform fundamental roles in nutrient cycling, especially nitrogen and phosphorus. Cyanobacteria contribute to carbon and nitrogen fixation and their cells act as phosphorus storages in ecosystems with extreme or oligotrophic environmental conditions such as those found in mangroves. As the high plant productivity in mangroves is only possible due to interactions with microorganisms, cyanobacteria may contribute to these ecosystems by providing fixed nitrogen, carbon, and herbivory-defense molecules, xenobiotic biosorption and bioremediation, and secreting plant growth-promoting substances. In addition to water, cyanobacterial colonies have been detected on sediments, rocks, decaying wood, underground and aerial roots, trunks, and leaves. Some mangrove cyanobacteria were also found in association to algae or seagrasses. Few studies on mangrove cyanobacteria are available, but together they have reported a substantial number of species in these ecosystems. However, the cyanobacterial diversity in this biome has been traditionally underestimated. Though mangrove communities generally host cyanobacterial taxa commonly found in marine environments, unique microhabitats found in mangroves potentially harbor several undescribed cyanobacterial taxa. The relevance of cyanobacteria for mangrove conservation is highlighted in their use for the recovery of degraded mangroves as biostimulants or in bioremediation.     

Central thermoregulatory effects of lactate in the toad Bufo paracnemis.

Hypoxia induces a regulated decrease in body temperature (Tb; anapyrexia) in organisms ranging from protozoans to mammals, but very little is known about the mechanisms involved. Several candidates have been suggested to mediate hypoxia-induced anapyrexia, among them lactate, which is a classical compansion of hypoxic stress in vertebrates. The present study was designed to assess the central thermoregulatory effects of lactate in Bujo paracnemis. Toads equipped with a temperature probe were tested over a thermal gradient (10-40 degrees C). Lactate injected systemically (4.0 mmol kg-1) caused a significant reduction of Tb from 24.6 +/- 2.1 to 17.4 +/- 3.9 degrees C. To assess the role of central thermoregulatory mechanisms, a lower dose (0.4 mmol kg-1) of lactate was injected into the fourth cerebral ventricle or systemically. Intracerebroventricular injection of lactate caused a similar decrease in Tb, whereas systemic injection caused no change. The data indicate that lactate may play a role in hypoxia-induced anapyrexia in central rather than peripheral sites.     

Locus-specific chromatin profiling of evolutionarily young transposable elements

Despite a vast expansion in the availability of epigenomic data, our knowledge of the chromatin landscape at interspersed repeats remains highly limited by difficulties in mapping short-read sequencing data to these regions. In particular, little is known about the locus-specific regulation of evolutionarily young transposable elements (TEs), which have been implicated in genome stability, gene regulation and innate immunity in a variety of developmental and disease contexts. Here we propose an approach for generating locus-specific protein–DNA binding profiles at interspersed repeats, which leverages information on the spatial proximity between repetitive and non-repetitive genomic regions. We demonstrate that the combination of HiChIP and a newly developed mapping tool (PAtChER) yields accurate protein enrichment profiles at individual repetitive loci. Using this approach, we reveal previously unappreciated variation in the epigenetic profiles of young TE loci in mouse and human cells. Insights gained using our method will be invaluable for dissecting the molecular determinants of TE regulation and their impact on the genome.