Antisense Knockdown of Zebrafish polr3b Generates a slj Phenocopy (A–D) Lateral views of 5-dpf and wild-type zebrafish larvae injected with vehicle (control [A]) or Morpholinos targeting either the polr3b translation initiation codon (polr3b-ATG MO [C]) or the polr3b exon 10 splice donor (polr3b-splice MO [D]). The intestine in both Morpholino-injected larvae resembles the slj intestine (B). (E–H) Corresponding images of the immunostained pancreas from these larvae: note that there is minimal exocrine tissue in larvae injected with either polr3b Morpholino, as occurs in slj. cpa, carboxypeptidase A; ins, insulin. (I) Agarose gel electrophoresis showing RT-PCR products amplified from polr3b cDNA derived from wild-type (WT) embryos injected with the polr3b-splice Morpholino. In both 24-hpf and 48-hpf larvae injected at the one-cell stage, a 155-bp band corresponding to in-frame deletion of exon 10 is evident (confirmed by DNA sequencing), but not in control larvae. The 278-bp wild-type fragment is also evident in the Morpholino-injected larvae.