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Fig. S2 appb morpholino (MO) injection leads to a dose-dependent disruption in appb mRNA processing. A. Zebrafish embryos were injected with increasing doses of appb MO and screened based on presence of morphological malformations and CNS cell death. B. The same experiments as in panel A revealed doses that were toxic to the developing fish. C. appb splice block MO is efficacious, as it leads to disruption of appb mRNA. RNA was isolated from fish injected with 2.5 ng appb MO, 1.0 ng appb MO, or an equivalent dose of control MO, and subjected to RT-PCR. Fish injected with 2.5 ng of the appb MO show a band at ~300 bp corresponding to retention of intron 3–4 in mRNA. This band is reduced when the dose of the MO is reduced, and absent when fish are injected with the control MO. Sequencing of the band confirmed the retention of intron 3–4 in mature mRNA, and predicted STOP codons in the modified mRNA. D. Embryos injected with the appb MO alone or with 200 pg of cognate appb mRNA. The instance of fish displaying a severe phenotype was significantly reduced and the number of normal fish was significantly increased upon inclusion of appb mRNA. **p<0.01. Colour coding in the histogram D is as per Fig. 2 and Fig. S1.