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The circadian clocks are vital to many organisms for their survival and adaption to the surrounding environment. More and more people are interested in the circadian clock and related researches. One of the key characteristics of this endogenous clock is its periodicity. Mechanisms underlying the mammalian circadian rhythms with ~24 h periodicity involve interlocked transcriptional and translational feedback loops. The circadian clock system in mammals consists of hierarchical structures, with the suprachiasmatic nucleus (SCN) as the central pacemaker and peripheral oscillators in other organs. In spite of the central and peripheral oscillators, the molecular mechanisms are the same within the SCN and peripheral organs. In the past decades, major achievements are accomplished by using forward and reverse genetics, as well as epigenetic approaches. In this review, we recapitulate the history of how clock-related genes were identified, and summarize the main achievements in genetics and epigenetics to understand the molecular underpinnings. We hope it can offer basic knowledge for further researches, a reference for experimental designs aiming to adjust organisms' homeostasis by modulating the clock, and provide a foundation to build interdisciplinary research networks.

Objective: To assess the safety and effectiveness of percutaneous transcatheter closure of atrial septal defect (ASD) under transesophageal echocardiography (TEE) guidance in children., Methods: The study included 20 cases of patients with ASD. The patients were (4.2 ± 1.2) years old and the mean body weights were (18.2 ± 4.2) kg. The diameter of ASD before closure was (13.4 ± 3.3) mm . All procedures were guided under TEE. Procedure success was evaluated by TEE immediately after procedure., Results: Closure devices were successfully implanted in all 20 patients under TEE guidance. The diameter of closure devices was 14-26 mm. There were no procedure related complications. The ventilation time was (2.9 ± 0.8)h and the hospitalization time was (3.2 ± 0.7) days., Conclusion: TEE guided percutaneous transcatheter closure is safe and effective for patients with ASD and avoids the radiation damages.