Alternative splicing of exons 14 and 16. RT-PCR products were amplified using primers flanking exon 14 (panels A and B), exon 16 (panels C and D) and exon 22a (panels E and F). Left panels: bands in lanes 1, 2, and 3 are from human fetal brain, mouse P1 brain, and mouse P60 brain total RNA, respectively. Right panels: bands in lanes 4, 5, 6 and 7 contain total RNA from cerebellum, brain stem, basal forebrain and cortex (P23), respectively. Transcripts containing both splice forms of exons 14, 16 and 22a were found in all lanes.