PABPN1 is required for normal myoblast proliferation. Pure cultures of primary mouse myoblasts from limb, pharyngeal and extraocular (EOM) muscles were transfected with one of two siRNA oligonucleotides for PABPN1 [PABPN1-1 (1) or PABPN1-2 (2)] or a scrambled control (C). Cells were labeled with BrdU and immunostained with anti-BrdU antibody. (A) Protein extracts were analyzed by immunoblotting for PABPN1 to confirm knockdown. Alpha-tubulin was used as a loading control. (B) Representative BrdU immunostaining after siRNA transfection (bar, 100 µm). DAPI staining was used for nuclear visualization. (C) The relative percentage of BrdU+ nuclei was determined in limb (L), pharyngeal (Ph) and extraocular (EOM) myoblasts and fibroblasts (F) transfected with siRNA. PABPN1 knockdown results in ∼40% decrease in the percentage of BrdU+ cells. Data are mean ± SE, *P < 0.05, n = 3.