Gene structure and mRNA variants of Fox-2. (A), Fox-2 gene structure. Mouse Fox-2 possesses 4 alternative promoters and contains 16 exons. Shaded boxes indicate alternatively spliced exons; open boxes, constitutive exons. Within the alternative exons, internal cryptic splice sites are used in exons 1A, 4, and 10, and generate exon variants designated as 1a′′, 1a′, 1a; 4′, 4; 10′, 10. A total of 4 alternative mutual exclusive translation initiation sites (ATG) are located in exons 1A 1D, 1E, or 1F. The RRM bar indicates the region that encodes for the RNA recognition motif (RRM). Splicing of exons 11 and 12 is mutually exclusive. (B) 5′ RACE analysis of the transcription initiation sites of Fox-2 from uninduced and induced MELCs. (C) RT-PCR analysis of mFox-2 expression in MELCs. RNAs were amplified with a primer set located at the first exon (1A, 1D, 1E, or 1F) and exon 16. MELC RNAs could be amplified with 1A or 1F primers but not with 1D or 1E primers. mRNAs from mouse brain and skeletal muscle served as positive controls for exon 1D and 1E, respectively. (D) Exon composition of Fox-2 isoforms isolated from mouse cells. mFox-2A and mFox-2F were isolated from MELCs. The same mFox-2F and an additional mFox-2F-S were isolated from C57/BL6 mouse muscle. (E) Exon composition of hFox-2 isoforms isolated from human cells. hFox-2F is expressed in HeLa cells. hFox-2F-4 and hFox-2F-5 are expressed in RD cells.