The Journal of Neuroscience, May 15, 2001, 21(10):3503-3514
Complex Trait Analysis of the Hippocampus: Mapping and Biometric
Analysis of Two Novel Gene Loci with Specific Effects on Hippocampal
Structure in Mice
Lu
Lu,
David C.
Airey, and
Robert W.
Williams
Center for Neuroscience, Department of Anatomy and Neurobiology,
University of Tennessee Health Science Center, Memphis, Tennessee 38163
Notable differences in hippocampal structure are associated with
intriguing differences in development and behavioral capabilities. We
explored genetic and environmental factors that modulate hippocampal size, structure, and cell number using sets of C57BL/6J (B6) and DBA/2J
(D2) mice; their F1 and F2 intercrosses (n = 180);
and 35 lines of BXD recombinant inbred (RI) strains. Hippocampal
weights of the parental strains differ by 20%. Estimates of granule
cell number also differ by ~20%. Hippocampal weights of RI strains range from 21 to 31 mg, and those of individual F2 mice range from 23 to 36 mg (bilateral weights). Volume and granule cell number are well
correlated (r = 0.7-0.8). Significant variation is
associated with differences in age and sex. The hippocampus increases
in weight by 0.24 mg per month, and those of males are 0.55 mg heavier
(bilateral) than those of females.
Heritability of variation is ~50%, and half of this genetic
variation is generated by two quantitative trait loci that map to chromosome 1 (Hipp1a: genome-wide
p < 0.005, between 65 and 100 cM) and to
chromosome 5 (Hipp5a, p < 0.05, between 15 and 40 cM). These are among the first gene loci known to
produce normal variation in forebrain structure. Hipp1a
and Hipp5a individually modulate hippocampal weight by
1.0-2.0 mg, an effect size greater than that generated by age or sex.
The Hipp gene loci modulate neuron number in the dentate
gyrus, collectively shifting the population up or down by as much as
200,000 cells. Candidate genes for the Hipp loci include
Rxrg and Fgfr3.
Key words:
dentate gyrus; granule cells; complex trait analysis; heritability; quantitative trait locus; BXD recombinant inbred strain; C57BL/6; DBA/2; spatial memory
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