Experiment
Twenty-five BXD RI strains, 1800 (C57BL/6J x DBA/2J)F2 intercross mice and 550 HS mice were used to identify acute ethnol locomotor response QTL. DBA/2J mice express stimulated locomotor activiity from moderate doses of ethanol while C57BL/6J are only mildly affected. The phenotypic data being measured were adaptation or habituation, thigmotaxis and time.
Candidate QTL were generated from the BXD RI data. A dataset of 400 unique markers, with an average spacing of 4cM, were used to analyze the RI data.QTLs meeting the threshold of a candidate QTL (p<.01) from the analysis of the RI strains for time dependent distance traveled were found on Chr 2 for time intervals 5-10, 10-15 and 15-20 min. Candidiate QTLs were also found on Chr 6 for time intervals 10-15 and 15-20 minutes and on Chr 1 for time interval 0-5 minutes. No significant RI strain effect was found for thigmotaxis.
To confirm the candidate QTL reciprocal F1 crosses between C57BL/6J and DBA/2J were used to generate a total of 1800 F2 mice. Onaverage 500 mice were genotyped at each of 82 markers which spanned the entire genome. An F value of >11.3 exceeded the LOD threshold of 4.3. Significant QTLs were detected in the F2 analysis on Chr 1 and 2.
On Chr 1, QTL Actre1 (activity response to ethanol 1) exceeded the highly significant threshold, F=15, for the 0-5 minute interval; and a suggestive QTL,(F=7), was identified for the 5 to 10 minute interval. Using both interval and composite interval mapping Actre1 mapped, between 80-90 cM on Chr 1.[Fig5]
On Chr 2 QTLs exceeding the highly significant threshold were detected at all time intervals, Actre7 at 0-5 minutes; Actre8 at 5-10 minutes; Actre9 at 10-15 minutes, and Actre10 at 15-20 minutes. Using both interval and composite mapping these four QTL peaked in a range between 40-90 cM on Chr 2. [Fig6]
Suggestive QTL were found on Chr 5 at the 5-10 and the 10-15 minute intervals.
No new QTL were detected in the F2 analysis that were not detected in the RI analysis; RI candidate QTL on Chr4and 6 were not confirmed. QTL analysis of the RI strain means for the adaptation phenotype detected a candidate QTL only on Chr X. The parallel F2 analysis did not confirm this candidate QTL.
HS mice from a cross of 8 inbred strains, C57BL/6J, DBA/2J,CBA/2J,C3H/HeJ, A/J, AKR/J, BALB/cJ and LP/J from G32 to G35 were analyzed. A total of 550 mice were phenotyped for the ethanol locomoter response (distance traveled). Authors state that using a diallele cross (B6 alleles vs non-B6 alleles) that they were unable to confirm the Chr 1 QTL detected in the F2 intercross; but that they did confirm the Chr 2 QTL.
12.07.2015 Curator Note: Because the strains comprising the HS mice differ from those of the RI strains and the F2 cross used here we consider the HS analysis a separate mapping experiment and have created unique QTL for the QTL detected in the differing experiments.
Using the HS mice the region of interest on Chr 2 decomposed into three separate linkage groups:
In the first linkage group characterizedby D2Mit94 and D2Mit436 a highly significant QTL, Actre2 (activity response to ethanol 2), was detected at the 10-15 minute time interval, F=16.0. The B6 allele was dominant with a trend towards overdominance at D2Mit94. Suggestive QTLs (F<11.3) were detected at time interval 0-5 min, F=2.2; 5-10 min, F=10.1 and 15-20 min, F=9.4.
No significant QTLs were detected in the second linkage group at D2Mit43.
The third linkage group, ranging from D2Mit207 (62.6cM) to D2Mit304 (70.1cM) detected two additive QTLs, Actre3 at D2Mit207 and Actre4 at D2Mit420, within the 10-15 minute interval. These were both characterized by dominant B6 alleles which increased the ethanol response accounting for 11% of the phenotypic variance. These QTL were not detected in the F2 intercross.
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