Pathological aggression in "fierce" mice corrected by human nuclear receptor 2E1

"Fierce" mice, homozygous for the deletion of nuclear receptor 2E1 (NR2E1), show abnormal brain-eye development and pathological aggression. To evaluate functional equivalency between mouse and human NR2E1, we generated mice transgenic for a genomic clone spanning the human NR2E1 locus and bred these animals to fierce mice deleted for the corresponding mouse gene. In fierce mutants carrying human NR2E1, structural brain defects were eliminated and eye abnormalities ameliorated. Excitingly, behavior in these "rescue" mice was indistinguishable from controls. Because no artificial promoter was used to drive transgene expression, promoter and regulatory elements within the human NR2E1 clone are functional in mouse. Normal behavior in rescue animals suggests that mechanisms underlying the behavioral abnormalities in fierce mice may also be conserved in humans. Our data support the hypothesis that variation at NR2E1 may contribute to human behavioral disorders. Use of this rescue paradigm with other genes will permit the direct evaluation of human genes hypothesized to play a causal role in psychiatric disease but for which evidence is lacking or equivocal.

Mutational-reporter transgenes rescued from mice lacking either Mgmt, or both Mgmt and Msh6 suggest that O6-alkylguanine-induced miscoding does not contribute to the spontaneous mutational spectrum

O6-methylguanine methyltransferase, Mgmt, constitutes the first line of defense against O6-alkylguanine, which can result in G : C to A : T transitions upon DNA replication. Mgmt has been found in organisms as diverse as archaebacteria and mammals. This evolutionary conservation suggests that all organisms may be exposed to either endogenous or environmental alkylating agents. We thus hypothesized that tissues of Mgmt-/- mice would exhibit elevated mutant frequencies. Employing the Big Blue trade mark transgenic system, we evaluated lacI mutants rescued from liver and small intestinal DNA of young Mgmt-/- mice. Interestingly, while there was a small difference between Mgmt-/- mice and controls with respect to lacI mutant frequency, no differences attributable to Mgmt deficiency were apparent in the mutational spectra. Although mutations stemming from O6-guanine alkylations would be predicted to be cumulative, we found no evidence of an Mgmt-dependent alteration in mutation spectrum in DNA samples from 12 month-old mice. To optimize our ability to detect mutations resulting from O6-alkylguanine-induced G : T mismatches, mice with combined deficiencies of Mgmt and the DNA mismatch repair molecule, Msh6, were analysed. In spite of this strategy, we observed no significant differences between Mgmt-/- Msh6-/- and Msh6-/- mouse lacI mutations, except for a trend towards a greater percentage (of total transitions) of G : C to A : T changes in Mgmt-/-Msh6-/- livers. Therefore, despite the striking evolutionary conservation of Mgmt, deficiency of this gene did not significantly impact the spontaneous lacI mutational spectrum in vivo.