Processes that regulate gene transcription are directly under the influence of the genome organization. The epigenome contains additional information that is not brought by DNA sequence, and generates spatial and functional constraints that complement genetic instructions. DNA methylation on CpGs constitutes an epigenetic mark generally correlated with transcriptionally silent condensed chromatin. Replication of methylation patterns by DNA methyltransferases maintains genome stability through cell division. Here we present evidence of an unanticipated dynamic role for DNA methylation in gene regulation in human cells. Periodic, strand-specific methylation/demethylation occurs during transcriptional cycling of the pS2/TFF1 gene promoter on activation by oestrogens. DNA methyltransferases exhibit dual actions during these cycles, being involved in CpG methylation and active demethylation of 5mCpGs through deamination. Inhibition of this process precludes demethylation of the pS2 gene promoter and its subsequent transcriptional activation. Cyclical changes in the methylation status of promoter CpGs may thus represent a critical event in transcriptional achievement.

In conclusion, the nested RT-PCR technique identified the presence of transcript encoding ERalpha mRNA in human skeletal muscles. Semi-quantification did not reveal gender difference.

It is well known that oestrogens exert muscle anabolic and metabolic effects. Oestrogens act via specific oestrogen receptor (ER) proteins. The mainly represented oestrogen receptor alpha messenger ribonucleic acid subtype (ER(alpha) mRNA) was described in various tissues including the skeletal muscle. Moreover, it has been shown that endurance training significantly increases ER(alpha) mRNA levels in the female rat gastrocnemius muscle. The aim of this study was to determine if this training programme also modifies ER(alpha) mRNA levels in muscles with different typology, the soleus (slow twitch muscle), extensor digitorum longus (fast twitch muscle) and gastrocnemius (intermediate muscle). So far, two groups of Wistar female rats were set up: untrained (u) (n = 7), and trained (e) (n = 7). The endurance training programme was performed for 7 weeks, 5 days per week and consisted of 1 h of continuous running on an adapted motor-driven treadmill involving progressive intensity and gradient of the treadmill. Three different skeletal muscles, extensor digitorum longus (E), gastrocnemius (G) and soleus (S), were isolated and weighed in the untrained (Eu, Gu and Su) and trained group (Ee, Ge and Se). Semi-quantification of ER(alpha) mRNA levels was performed by the reverse transcriptase-polymerase chain reaction (RT-PCR) technique. In order to attest the efficiency of our endurance training programme, the citrate synthase activity (CS) of each muscle was measured by a fluorimetric method. The CS activity was significantly increased with training in the gastrocnemius [100.00 +/- 4.99% in Gu (n = 6) vs. 138.10 +/- 8.82% in Ge (n = 6), P < 0.01] and in the soleus [100.00 +/- 2.92% in Su (n = 7) vs. 115.90 +/- 3.71% in Se (n = 7), P < 0.01] but not in the extensor digitorum longus [100.00 +/- 1.87% in Eu (n = 7) vs. 96.90 +/- 1.55% in Ee (n = 7)]. Concerning the influence of muscle type on ER(alpha) mRNA level (1) in the untrained group, the ER(alpha) mRNA level was significantly higher in soleus muscle compared with gastrocnemius and extensor digitorum longus muscles [0.43 +/- 0.04 in Su (n = 7) compared with 0.31 +/- 0.03 in Gu (n = 6) and 0.21 +/- 0.03 in Eu (n = 7), P < 0.05; P < 0.05); 2] in the trained group, the ER(alpha) mRNA level was significantly higher insoleus and gastrocnemius muscles compared with extensor digitorum longus muscle [0.43 +/- 0.06 in Se (n = 7) and 0.49 +/- 0.05 in Ge (n = 6) vs. 0.12 +/- 0.01 in Ee (n = 7), P < 0.05; P < 0.05]. Indeed, after training, the ER(alpha) mRNA level significantly increased in gastrocnemius muscle [0.31 +/- 0.03 in Gu(n = 6) vs. 0.49 +/- 0.05 in Ge (n = 6), P < 0.01], significantly decreased in extensor digitorum longus [0.21 +/- 0.03 in Eu (n = 7) vs. 0.12 +/- 0.01 in Ee (n = 7), P < 0.01] and was not significantly modified in soleus [0.43 +/- 0.04 in Su (n = 7) vs. 0.43 +/- 0.06 in Se (n = 7)]. The differences in ER(alpha) mRNA level between trained and untrained animals indicate training-induced effects that are specific to the skeletal muscle type.

Endurance training induces, in female rats, alterations of oestrous cycle with decrease in plasma oestradiol levels. Moreover, it is well known that oestradiol concentrations modify oestrogen receptor levels. In order to further explain the effects of oestrogens on skeletal muscles, we hypothesized that endurance training modifies the levels of oestrogen receptor alpha messenger ribonucleic acid (ER alpha mRNA) in rat gastrocnemius muscle. Wistar rats were separated into four groups: male controls (C(m)) (n=7), female controls (C(f)) (n=6), male trained (E(m)) (n=7) and female trained (E(f)) (n=6). The endurance training programme was performed for 7 weeks, 5 days week-1 and consisted of 1 h of continuous running on an adapted motor-driven treadmill. At the end of the training session, the gastrocnemius muscle was isolated, weighed and semiquantification of ER alpha mRNA was performed using the reverse transcriptase-polymerase chain reaction (RT-PCR) technique. The citrate synthase (CS) activity of the gastrocnemius muscle was measured by a fluorimetric method. The CS activity of the male and female gastrocnemius muscle, respectively, 100 +/- 7% in C(m) (n=7) vs. 120 +/- 14% in E(m) (n=6, P < 0.01) and 100 +/- 13% in C(f) (n=6) vs. 138 +/- 23% in E(f) (n=6, P < 0.01) was significantly increased after 7 weeks of training. The ER alpha mRNA levels were significantly increased in E(f) compared with C(f) (0.49 +/- 0.15 vs. 0.31 +/- 0.11, P < 0.01) but not in E(m) compared with C(m) (0.37 +/- 0.15 vs. 0.37 +/- 0.13). In conclusion, these results demonstrate that 7 weeks of endurance training increased the level of transcripts encoding ER alpha in rats with the increase restricted to the females.