Fig. 1. NFAT5 expression and activity during myogenesis in vivo. (A) Immunostaining of TA sections from uninjured mice with an anti-NFAT5 antibody revealed a diffuse low level of staining throughout the section. No immunostaining was observed in sections following incubation with control IgG. Serial sections were stained with hematoxylin and eosin (H&E). Bar, 50 µm. (B) Immunostaining of TA sections 3 and 4 days following injury with an antibody against NFAT5 indicated bright staining of both mononucleated cells (^*) and regenerating myofibers. NFAT5 appeared both nuclear (arrows) and cytoplasmic in newly formed myofibers (day 4). Arrow indicates the same myofiber in both sections. Bar, 50 µm. (C) TA muscles were electroporated with either an NFAT5 or control (C) reporter. Muscles were homogenized after 6 days and luciferase activity was determined. NFAT5 was transcriptionally active in vivo. Data are expressed as fold increase in luminescence relative to the control reporter containing mutated NFAT5 binding sites. Data are mean ± s.e.m. from four mice. (D) TA muscles were electroporated with a construct encoding ß-gal and collected 6 days later. ß-gal activity was confined to regenerating areas. The H&E stained section is a higher magnification view of the area in the indicated rectangle on the ß-gal stained section. Bar, 100 µm.