Fig. 5

One of the three transcripts of fhf2a is cardiac-specific. A: Scheme of the 1 MB genomic region on chromosome 14, where transposons of CCS enhancer trap lines (SqET33-mi28, SqET33-mi59B) are inserted closest to fhf2a/fgf13. zic3, mcf2, atp11c and sox3 are encoded in the reverse strand. B: Gene structure of zebrafish fhf2a highlights its three alternatively spliced variants and transposon insertion sites. The three fhf2a transcripts differ due to differentially spliced first exons, with exon 1S located 2.2 Kb, exon 1U - 6.1 Kb and exon 1Y + 1V - 52 Kb away from shared exon 2. The three transcripts share the common exons 2-5, which encode putative peptides that are 100% identical in amino acid sequence. The ATG (red flag), stop site (black post) and the sizes of introns and exons are indicated. C-F: 1S is the cardiac fhf2a transcript with expression in a SAN at 3 dpf. C: WISH of a 3 dpf embryo with the fhf2a(1S)-specific probe. D,E: Sagittal sections at the level of the 3 dpf heart (D: fhf2a(e2-5)-specific probe; E: fhf2a(1S)-specific probe). White arrows - the base of the heart. F: one step RT-PCR on 3 dpf hearts RNA (top) and brains RNA (bottom). Only the 1S splice variant is expressed in the heart. ef1a - the loading control for PCR. G-N: Distinct expression of fhf2a splice variants as shown by WISH on 3 dpf embryos using isoform specific probes: common exons refer to e2-e5 shared among all three isoforms - G, K; fhf2a(1Y + 1V) - H, L; fhf2a (1U) - I, M and fhf2a (1S) - J, N. Green arrows: dorsal diencephalon; orange arrows: dorsal root ganglia and red arrows.