analysis-cardiomyocyte-development-using-immunofluorescence-embryonic

Analysis of Cardiomyocyte Development using Immunofluorescence in Embryonic Mouse Heart

During heart development, the generation of myocardial-specific structural and functional units including sarcomeres, contractile myofibrils, intercalated ...

Northwestern University

University of California, San Francisco

A conserved transcription-translation negative feedback loop forms the molecular basis of the circadian oscillator in animals. Molecular interactions within this loop have been relatively well characterized in vitro and in cell culture; however, in vivo approaches are required to assess the functional significance of these interactions. Here, regulation of circadian gene expression was studied in vivo by using transgenic reporter mouse lines in which 6.75 kb of the mouse Period1 (mPer1) promoter drives luciferase (luc) expression. Six mPer1-luc transgenic lines were created, and all lines express a daily rhythm of luc mRNA in the suprachiasmatic nuclei (SCN). Each mPer1-luc line also sustains a long-term circadian rhythm of luminescence in SCN slice culture. A 6-h light pulse administered during the early subjective night rapidly induces luc mRNA expression in the SCN; however, high luc mRNA levels are sustained, whereas endogenous mPer1 mRNA levels return to baseline, suggesting that posttranscriptional events mediate the down-regulation of mPer1 after exposure to light. This approach demonstrates that the 6.75-kb mPer1 promoter fragment is sufficient to confer both circadian and photic regulation in vivo and reveals a potential posttranscriptional regulatory mechanism within the mammalian circadian oscillator.

Photic and circadian expression of luciferase in mPeriod1-luc transgenic mice invivo.

The basic helix-loop-helix (bHLH)-Per-Arnt-Sim (PAS) domain transcription factor BMAL1 is an essential component of the mammalian circadian pacemaker. Bmal1-/- mice lose circadian rhythmicity but also display tendon calcification and decreased activity, body weight, and longevity. To investigate whether these diverse functions of BMAL1 are tissue-specific, we produced transgenic mice that constitutively express Bmal1 in brain or muscle and examined the effects of rescued gene expression in Bmal1-/- mice. Circadian rhythms of wheel-running activity were restored in brain-rescued Bmal1-/- mice in a conditional manner; however, activity levels and body weight were lower than those of wild-type mice. In contrast, muscle-rescued Bmal1-/- mice exhibited normal activity levels and body weight yet remained behaviorally arrhythmic. Thus, Bmal1 has distinct tissue-specific functions that regulate integrative physiology.

Article	Year
Photic and circadian expression of luciferase in mPeriod1-luc transgenic mice invivo. Proceedings of the National Academy of Sciences of the United States of America\| PubMed ID: 11752392	2002
Dissecting the functions of the mammalian clock protein BMAL1 by tissue-specific rescue in mice. Science (New York, N.Y.)\| PubMed ID: 17124323	2006

Lisa D. Wilsbacher

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