Description of the Men1 mouse model used in the analysis. (a) Schematic representation of the mutant and of the wild-type allele of the Men1 gene in the heterozygous Men1 mutant mice. Black boxes and lines represent exons and introns respectively. The grey horizontal arrow depicts a loxP sequence, and the black vertical arrow shows the location of the premature stop codon generated by exon 3 deletion. The strategy used to delete Men1 exon 3 in mice has been described previously . (b) Transcript copy number were measured by quantitative RT-PCR using 50 pg of RNA extracted from Men1+/Δ mouse embryonic fibroblasts (MEF) untreated or treated with puromycin (Puro). Specific amplification of either the wild-type (WT) or the mutant (Mu) transcript lacking exon 3 was achieved using the primers described in the Methods section.