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Fig. 1 sall4 is required for pectoral fin outgrowth. (A-C) sall4 expression during zebrafish pectoral fin development. (A) Section through the pectoral fins at 22 hpf. Lateral view of the fin buds at 32 hpf (B) and 48 hpf (C). (D) Schematic of the RT-PCR used to test the efficiency of a sall4 splice-blocking MO. Bands of 255 bp and 345 bp represent spliced and unspliced sall4 mRNA, respectively. Arrows represent primers used in the RT-PCR and the black box represents the sall4 MO. (E) The RT-PCR was performed on wild-type embryos and embryos injected with 5 ng of the sall4 MO. The sall4 MO efficiently blocks sall4 mRNA splicing. There was no inhibition of sall4 splicing in embryos injected with 5 ng of a 5 bp mismatch control sall4 MO (con. MO, control MO; M, DNA molecular weight marker). (F-K) Dorsal views of the pectoral fins of 3 dpf embryos. (F) Wild-type embryo. (G-J) Embryos injected with 5 ng of sall4 MO. The percentages of phenotypes observed at 3 dpf following injection of different concentrations of sall4 MO is listed below each picture. (K) Upturned pectoral fin phenotype produced following injection of 1 ng of tbx5 MO. Arrows highlight the pectoral fin defects in G-K. (L-O) Pectoral fins (5 dpf) stained with Alcian Blue. (L) Wild type. (M-O) The pectoral fins of embryos injected with 4 ng of sall4 MO. Scale bars: 75 µm. cl, cleithrum; sc, scapulocoracoid; pop, postcoracoid process; ed, endoskeletal disc; ac, actinotrichs.