Muscle Contraction Induces Acute Hydroxymethylation of the Exercise-Responsive Gene <i>Nr4a3</i>

Exercise training triggers numerous positive adaptations through the regulation of genes controlling muscle structure and function. Epigenetic modifications, including DNA methylation, participate in transcriptional activation by allowing the recruitment of the transcription machinery to gene promoters. Exercise induces dynamic DNA demethylation at gene promoters; however, the contribution of the demethylation precursor hydroxymethylcytosine is unknown. Given the evanescent nature of hydroxymethylcytosine, a muscle contraction model that allows for the collection of samples that are repeatedly stimulated over time is required to determine whether contraction-induced demethylation is preceded by changes in the hydroxymethylcytosine level. Here, we established an acute skeletal muscle contraction model to mimic the effects of acute exercise on gene expression. We used this model to investigate the effect of muscle contraction on DNA demethylation and hydroxymethylation. First, we performed an acute exercise study in healthy humans to identify an exercise-responsive gene that we could study in culture. We identified the nuclear receptor subfamily 4 group A member 3 (Nr4a3) gene with the highest fold-expression increase after acute exercise. We then refined an electrical pulse stimulation (EPS) protocol that could induce expression of the Nr4a3 gene in C2C12 myotubes. Using targeted bisulfite sequencing, we found that in response to EPS, a region of the Nr4a3 promoter is rapidly demethylated at 60 min and re-methylated at 120 min. Of interest, hydroxymethylation of the differentially methylated region of Nr4a3 promoter after EPS was elevated immediately after EPS, with lowest levels reached at 60 min after EPS. In conclusion, we have established a cell culture-based protocol to mimic the acute transcriptional responses to exercise. Furthermore, we provide insight into the mechanism by which the exercise-responsive gene Nr4a3 is demethylated after muscle contraction

Frequency response of renal sympathetic nervous activity to aortic depressor nerve stimulation in the anaesthetized rat

The contribution of central baroreceptor reflex pathways to the dynamic regulation of sympathetic nervous activity (SNA) has not been properly examined thus far. The aim of this study was to characterize the transfer function of the central arc of the baroreceptor reflex (from baroreceptor afferent activity to SNA) over a wide range of frequencies.In nine baroreceptor-intact and six sino-aortic baroreceptor-denervated rats anaesthetized with urethane, the renal SNA was recorded while applying sinusoidal stimulation to the aortic depressor nerve at 26 discrete frequencies ranging from 0.03 to 20 Hz. At each modulation frequency, cross-power spectrum analysis using a fast Fourier transform algorithm was performed between the stimulation and renal SNA, which provided the transfer function of the central arc.In both baroreceptor intact and denervated rats, the transfer gain increased by a factor of about three between 0.03 and 1 Hz. At higher frequencies, the gain decreased but remained above the static gain of the system up to 12 Hz. There was a slight phase lead up to 0.4 Hz, then a continuously increasing phase lag. A three-element linear model satisfactorily described the experimental transfer function. The model combined a derivative gain (corner frequency ∼0.15 Hz), an overdamped second-order low-pass filter (natural frequency ∼1 Hz) and a fixed time delay (∼100 ms).These results indicate that the central arc of the baroreceptor reflex shows derivative properties that are essential for compensating the filtering of fast oscillations of baroreceptor afferent activity and thus for the generation of fast oscillations of renal SNA (e.g. those related to the cardiac cycle)

Data from: Understanding the recent colonization history of a plant pathogenic fungus using population genetic tools and Approximate Bayesian Computation

Understanding the processes by which new diseases are introduced in previously healthy areas is of major interest in elaborating prevention and management policies as well as in understanding the dynamics of pathogen diversity at large spatial scale. In this study, we aimed to decipher the dispersal processes that have led to the emergence of the plant pathogenic fungus Microcyclus ulei, which is responsible for the South American Leaf Blight (SALB) that has affected rubber trees across Latin America since the beginning of the twentieth century. As only imprecise historical information is available, the study of population evolutionary history based on population genetics appeared most appropriate. The distribution of genetic diversity in a continental sampling of four countries (Brazil, Ecuador, Guatemala and French Guiana) was studied using a set of 16 microsatellite markers developed specifically for this purpose. A very strong genetic structure was found (Fst = 0.70), demonstrating that there has been no regular gene flow between Latin American M. ulei populations. Strong bottlenecks probably occurred at the foundation of each population. The most likely scenario of colonization identified by the Approximate Bayesian Computation (ABC) method implemented in DIYABC suggested two independent sources from the Amazonian endemic area. The Brazilian, Ecuadorian and Guatemalan populations might stem from serial introductions through human-mediated movement of infected plant material from an unsampled source population, whereas the French Guiana population seems to have arisen from an independent colonization event through spore dispersal