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1From the Institute of Developmental Genetics, 2Institute of Stem Cell Research, 3Institute of Experimental Genetics, and 5Institute of Human Genetics, GSFNational Research Center for Environment and Health, Neuherberg, Germany; 4Institute of Molecular Genetics, Max-Delbrück-Center for Molecular Medicine, Berlin, Germany; 6RiskMuTox, Oak Ridge, Tennessee; and 7Lehrstuhl für Molekulare Tierzucht und Biotechnologie, Ludwig-Maximilians-Universität, Munich, Germany.
PURPOSE. To characterize three new mouse small-eye mutants detected during ethylnitrosourea mutagenesis programs.
METHODS. Three new mouse small-eye mutants were morphologically characterized, particularly by in situ hybridization. The mutations were mapped, and the candidate gene was sequenced. The relative amount of Pax6-specific mRNA was determined by real-time PCR. Reporter gene analysis used Crygf and Six3 promoter fragments in front of a luciferase gene and HEK293 cells as recipients.
RESULTS. The new mutationsADD4802, Aey11, and Aey18were mapped to chromosome 2; causative mutations have been characterized in Pax6 (Aey11: C
T substitution in exon 8, creating a stop codon just in front of the homeobox; ADD4802: G
A substitution at the beginning of intron 8 changes splicing and leads to an altered open reading frame and then to a premature stop codon; Aey18: G
A exchange in the last base of intron 5a leads also to a splice defect, skipping exons 5a and 6). Real-time PCR indicated nonsense-mediated decay in Pax6Aey11 and Pax6Aey18 mutants but not in Pax6ADD4802. This result is supported by the functional analysis of corresponding expression constructs in cell culture, where the Aey11 and Aey18 alleles did not show a stimulation of the Six3 promotor or an inhibition of the Crygf promoter (as wild-type constructs do). However, the Pax6ADD4802 allele stimulated both promoters.
CONCLUSIONS. Together with functional analysis in a reporter gene assay and immunohistochemistry using Pax6 antibodies, it is suggested that the Pax6Aey11 and Pax6Aey18 alleles act through a loss of function, whereas ADD4802 represents a gain-of-function allele.
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