Fig. 4.

Alterations in frataxin mRNA expression in extracardiac tissues in the MCK mutant (Fxn knockout) mice relative to the WT mice are not due to Fxn deletion. (A) Conditional deletion of mouse frataxin exon 4 as reported previously (7). From top to bottom: WT allele, loxP-flanked Fxn exon 4 allele (L3), and Cre-mediated exon 4 deleted allele (Δ). The Δ allele was derived from the exon 4 deletion of the L3 allele via a cross with a CMV-Cre line (7). Flag, loxP site; B, BamHI; E, exon; P, primer; X, XbaI; X^o, modified XbaI. (B) The L3 allele was identified in the liver, kidney, and spleen, but not the heart, of the mutants, demonstrating the muscle-specific deletion of exon 4. This results in the Δ allele in the mutant heart only. PCR conditions were as described previously (7, 11). (C) RT-PCR showing pronounced down-regulation of frataxin mRNA in the heart and less marked reductions in the liver and kidney of 10-week-old mutants relative to WT mice of the same age. Densitometry data are reported as the mean ± SD of 3 experiments. *, P < .05; **, P < .01; ***, P < .001.