Fig. 4

Ectopic expression of human APP₆₉₅ rescues the APPb morphant phenotype.( A) Morphology of live embryos at 48 hpf. Lateral views, anterior to the left and dorsal up. Embryos were uninjected (1), control-MO-injected (2), APPb-MO-injected (3), or co-injected with APPb-MO and APP₆₉₅ mRNA (4). Note that co-injection with APP₆₉₅ mRNA rescued the developmental defects. A higher magnification of the tail region showed an elongated ‘stack of pennies’ notochord in uninjected (5) and control-MO-injected (6) embryos, compared to an undulating notochord and a curly tail in APPb-MO-injected embryos (7). Embryos co-injected with APPb-MO and APP₆₉₅ mRNA (8) revert to an elongated tail and ‘stack of pennies’ notochord that is similar to controls. (B) Quantification of embryo rescue through co-injection of mRNA. Injection of 10 ng of APPb-MO causes the defective phenotype (shortened axis, curly tail) in 75% of embryos (blue bars). Co-injection with mRNA encoding full-length APP₆₉₅ (purple bars) results in an increase in the normal-to-mild phenotypes, compared to APPb-MO-injected embryos (blue bars) that have increased moderate-to-severe phenotypes, indicating rescue of the curly tail morphant phenotype with APP₆₉₅ mRNA. ∗∗∗ is p = 0.0002, p < 0.05 in two-tailed unpaired t-test; Gaussian distribution; N of experiments = 14; N of embryos ∼ 300. Similarly, embryos co-injected with APPb-MO with sAPPα ectodomain (green bars) showed an increase in normal-to-mild phenotypes in comparison to APPb-MO-injected embryos. ∗∗p = 0.0037 for sAPPα with Mann–Whitney test N of experiments = 8. Total N of embryos analyzed = 143. In contrast, cΔ18 mRNA co-injected embryos (red bars) had a similar number of normal-to-mild phenotypes as APPb-MO-injected embryos, indicating cΔ18 mRNA does not rescue the morphant phenotype. p > 0.05, Mann–Whitney test for cΔ18. Error bars represent ± standard error of mean (S.E.M).