Quantitative trait locus analysis of abnormal circadian period in CS mice

CS mice show a free-running period (κ) longer than 24 h and rhythm splitting in constant darkness (DD). These features in behavioral circadian rhythms are distinctive as compared with other inbred strains of mice, which exhibit robust free-running rhythms with κ shorter than 24 h. To identify the genes affecting κ, quantitative trait locus (QTL) analysis was initially conducted by using 289 F₂ mice derived from a cross between CS and C57BL/6J strain. A suggestive QTL (LOD = 3.71) with CS allele increasing κ was detected on the distal region of Chromosome (Chr) 19. Next, using 192 F₂ mice from a cross between CS and MSM strain, the presence of the QTL on Chr 19 was examined, and we confirmed the QTL at the genome-wide significant level (LOD = 4.61 with 10.4% of the total variance explained). This QTL was named long free-running period (Lfp). Three other suggestive QTLs (LOD = 3.24–4.28) were mapped to the midportion of Chr 12 in (CS×C57BL/6J)F₂ mice, and to the proximal and middle region of Chr 19 in (CS×MSM)F₂ mice, respectively, of which, CS alleles for two QTLs on Chr 19 have the effect of lengthening κ. None of these QTLs were mapped to the chromosomal regions of previously described QTLs for κ and known clock genes (Clock, mPer1, Bmal1, mCry1, mCry2, mTim, and Csnk1e). Received: 5 July 2000 / Accepted: 5 December 2000