International Mammalian Genome Society

The 14th International Mouse Genome Conference (2000)

F4. Chimeric Analysis of the Effects of the Clock Mutation on Circadian Behavior in Mice

Sharon S. Low-Zeddies1 and Joseph S. Takahashi1,2
2Howard Hughes Medical Institute,
NSF Center for Biological Timing, Department of Neurobiology and Physiology, Institute for Neuroscience, Northwestern University, Evanston, IL 60208.

Circadian rhythms in locomotor activity have been extensively characterized in the mouse. This complex behavior is under the control of the suprachiasmatic nucleus (SCN), a defined pair of cell clusters in the hypothalamus.

Mice homozygous for the Clock mutation express 28-29 hour circadian periods and low amplitude circadian rhythmicity, or arrhythmicity, in constant conditions (Vitaterna et al., '94) whereas wild-type mice exhibit strong circadian rhythmicity with periods close to 23.5 hours in length. These phenotypic differences manifest at the level of single SCN cells in vitro (Herzog et al., '98). We have produced 130 Clock/Clock; +/+ < -- > +/+; ROSA 26 aggregation chimeras to study how cells of contrasting genotypes functionally interact within the intact SCN.

All tissues in each chimeric individual, including the SCN, come to be finely populated by the two cellular genotypes, in unique proportions and patterns. Across a spectrum of Clock chimeras, circadian behavioral phenotypes spanned a range from wild-type-like to Clock/Clock mutant-like. Intermediate circadian phenotypes had never been observed in tissue transplantation studies of individuals incorporating functional SCN tissues from mutant and wild-type tau hamsters (Vogelbaum & Menaker, '92). Furthermore, about 1/3 of our chimeras, whose SCN comprised roughly equal genotypic proportions, exhibited a variety of novel combinations of circadian period, amplitude, and phase-shift responses to light. We present quantitative analyses of the relationship between these behavioral measures and the proportion, and spatial distribution, of the cellular genotypes within the chimeric SCN. Using multivariate statistical techniques to summarize these measures, we show how complex phenotypes can be usefully organized and evaluated. We also demonstrate the potential of large-scale aggregation chimera analysis for the genetic dissection of phenotypes arising from transgenic and targeted genome alterations, as well as mutations like Clock such as are currently being identified in mouse mutagenesis screens worldwide.

Supported by the NSF Center for Biological Timing, an Unrestricted Grant in Neuroscience from Bristol-Myers Squibb and the National Institute of Mental Health. J. S. Takahashi is an Investigator in the Howard Hughes Medical Institute.

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