Fig. 1.

Bitransgenic animals expressing either 0 or 960 CUG repeats within exon 15 of the DMPK gene. (A) Transgene driven by the CMV enhancer was created with a floxed concatemer of three polyadenylation sites followed by exon 15 of the DMPK gene with either 0 (designated EpA0) or 960 (EpA960) CTG repeats (19). EpA lines transcribe RNAs that terminate at one of the three polyadenylation sites. Cre-mediated recombination induces expression of mRNA containing DMPK exon 15 with [EpA960(R)] or without [EpA0(R)] CUG repeats. (B) Quantitative RT-PCR performed on RNA extracted from gastrocnemius muscle in EpA960/HSA-Cre-ER^T2 mice (n = 5 for each group) and EpA0/HSA-Cre-ER^T2 mice (n = 3 for each group) before and 4 weeks after tamoxifen administration. GAPDH was used as a standard. Differences in mRNA levels from the recombined allele [EpA0(R) or EpA960(R)] between pre- and posttamoxifen in EpA960/HSA-Cre-ER^T2 and EpA0/HSA-Cre-ER^T2 mice were statistically significant (*) as assessed by Student's t test, P < 0.05. (C) Expression of mRNA from the recombined allele in different muscle groups (Quad, quadriceps; Gas, gastrocnemius; Sol, soleus; Tri, triceps; Dia, diaphragm) in EpA960/HSA-Cre-ER^T2 mice 4 weeks after tamoxifen. There is no statistically significant difference between the five muscle groups using one-way ANOVA, n = 3 for each group.