Manipulation of mammalian cell lines for circadian studies.

In mammals, the central circadian pacemaker resides in the hypothalamic suprachiasmatic nucleus (SCN), but circadian oscillators also exist in peripheral tissues. We have used wild-type and cryptochrome (mCry)-deficient mouse embryonic fibroblasts (MEFs) to demonstrate that the peripheral oscillator is mechanistically very similar to the oscillator in the SCN. Following serum shock activation, fibroblasts are able to sustain an SCN-like temporal expression profile of all known genes (i.e., antiphase oscillation of Bmal1 and Dbp genes), but are not able to produce oscillations in the absence of functional mCry genes. Remarkably, the analysis of mCry1-/- and mCry2-/- MEFs revealed the capacity to control period length in immortalized cell lines. Thus, the use of mammalian cells has become one of the most convenient methods for monitoring the molecular clock machinery and analyzing clock proteins at the functional/structural level. Here, we present the necessary protocols to (1) derive and culture a fibroblast cell line from wild-type and knockout mouse skin and (2) transfect cells at high efficiency to use in functional clock-protein studies.