Mortality in Sec23b-deficient ZF between 18 and 21 d is rescued by Sec23a. (A and B) sec23b heterozygous (sec23b^+/−) ZF with a 53-bp deletion were generated with CRISPR/Cas9. Binucleated erythrocyte counts from peripheral blood of ZF offspring from a sec23b^+/− × sec23b^+/− intercross were evaluated by two independent investigators blinded to the ZF genotype. (C) sec23b^−/− ZF exhibit indistinguishable o-dianisidine staining compared with WT clutchmate controls. Scores 1–3 correspond to staining intensities (3 = highest staining intensity). (D) sec23b^−/− ZF (generated from sec23b^+/− intercrosses) die between 18 and 21 d. (E) H&E stains of sec23b^−/− and WT ZF at day 16. sec23b^−/− ZF appear histologically normal. (Magnification: 10×.) (F) One-cell–stage embryos generated from sec23b^+/− ZF intercrosses were injected with a vector (designed to integrate in the ZF genome) that expresses Sec23a and GFP or GFP alone as control. Genotyping at 4 wk of age demonstrates rescue of sec23b^−/− mortality by Sec23a. (G) PCR genotyping assay demonstrating 2 sec23b^−/− ZF, expressing Sec23a from a ubiquitin promoter, alive at 4 wk of age.

sec23b^-/- ZF histology and GFP expression of ZF injected with a vector (designed to integrate into the ZF genome) expressing Sec23a and GFP from a ubiquitin promoter.

(A) sec23b^-/- ZF exhibit normal pancreas histology at day 16 and (B) normal staining with o-dianisidine at day 7 compared to WT clutchmate controls. (C) The sec23a cDNA is expressed from a ubiquitin promoter with a P2A sequence separating it from a sequence encoding GFP. (D) Ubiquitous Sec23A expression (approximated by GFP), as expected from vector integration into onecell stage embryos.