BackgroundRecombinant inbred (RI) strains of mice are an important resource used to map and analyze complex traits. They have proved particularly effective in multidisciplinary genetic studies. Widespread use of RI strains has been hampered by their modest numbers and by the difficulty of combining results derived from different RI sets.ResultsWe have increased the density of typed microsatellite markers two- to five-fold in each of several major RI sets that share C57BL/6 as a parental strain (AXB, BXA, BXD, BXH and CXB). A common set of 490 markers was genotyped in just over 100 RI strains. Genotypes of around 1,100 additional microsatellites in one or more RI sets were generated, collected and checked for errors. Consensus RI maps that integrate genotypes of approximately 1,600 microsatellite loci were assembled. The genomes of individual strains typically incorporate 45-55 recombination breakpoints. The collected RI set - termed the BXN set - contains approximately 5,000 breakpoints. The distribution of recombinations approximates a Poisson distribution and distances between breakpoints average about 0.5 centimorgans (cM). Locations of most breakpoints have been defined with a precision of < 2 cM. Genotypes deviate from Hardy-Weinberg equilibrium in only a small number of intervals.ConclusionsConsensus maps derived from RI strains conform almost exactly to theoretical expectation and are close to the length predicted by the Haldane-Waddington equation (x3.6 for a 2-3 cM interval between markers). Non-syntenic associations between different chromosomes introduce predictable distortions in quantitative trait locus (QTL) datasets that can be partly corrected using two-locus correlation matrices.

Respiration is controlled by central pattern generating circuits in the brain stem, whose activity can be modulated by inputs from other brain areas to adapt respiration to autonomic and behavioral demands. The cerebellum is known to be part of the neuronal circuitry activated during respiratory challenges, such as hunger for air, but has not been found to be involved in the control of spontaneous, unobstructed breathing (eupnea). Here we applied a measure of intrinsic rhythmicity, the CV2, which evaluates the similarity of subsequent intervals and is thus sensitive to changes in rhythmicity at the temporal resolution of individual respiratory intervals. The variability of intrinsic respiratory rhythmicity was reduced in a mouse model of cerebellar ataxia compared to their healthy littermates. Irrespective of that difference, the average respiratory rate and the average coefficient of variation (CV) were comparable between healthy and ataxic mice. We argue that these findings are consistent with a proposed role of the cerebellum in modulating the duration of individual respiratory intervals, which could serve to purpose of coordinating respiration with other rhythmic orofacial movements, such as fluid licking and swallowing.

A quantitative long-term fluid consumption and fluid licking assay was performed in two mouse models with either an ~ 2Mb genomic deletion, Df(11)17, or the reciprocal duplication CNV, Dp(11)17, analogous to the human genomic rearrangements causing either Smith-Magenis syndrome [SMS; OMIM #182290] or Potocki-Lupski syndrome [PTLS; OMIM #610883], respectively. Both mouse strains display distinct quantitative alteration in fluid consumption compared to their wild-type littermates; several of these changes are diametrically opposing between the two chromosome engineered mouse models. Mice with duplication vs. deletion showed longer vs. shorter intervals between visits to the waterspout, generated more vs. less licks per visit and had higher vs. lower variability in the number of licks per lick-burst as compared to their respective wild-type littermates. These findings suggest that copy number variation can affect long-term fluid consumption behavior in mice. Other behavior differences were unique for either the duplication or deletion mutants; the deletion CNV resulted in increased variability of the licking rhythm, and the duplication CNV resulted in a significant slowing of the licking rhythm. Our findings document a readily quantitated complex behavioral response that can be directly and reciprocally influenced by a gene dosage effect.

28Respiration is controlled by central pattern generating circuits in the brain 29 stem, whose activity can be modulated by inputs from other brain areas to adapt 30 respiration to autonomic and behavioral demands. The cerebellum is known to be 31 part of the neuronal circuitry activated during respiratory challenges, such as hunger 32 for air, but has not been found to be involved in the control of unobstructed breathing 33 at rest (eupnea). Here we applied a measure of intrinsic rhythmicity, the CV2, which 34 evaluates the similarity of subsequent intervals and is thus sensitive to changes in 35 rhythmicity at the temporal resolution of individual respiratory intervals. The 36 variability of intrinsic respiratory rhythmicity was reduced in a mouse model of 37 cerebellar ataxia compared to their healthy littermates. Irrespective of that 38 difference, the average respiratory rate and the average coefficient of variation (CV) 39 were comparable between healthy and ataxic mice. We argue that these findings are 40 consistent with a proposed role of the cerebellum in the coordination of respiration 41 with other rhythmic orofacial movements, such as fluid licking and swallowing. 42 43 44 45