Gene editing of the GJB2 locus in porcine embryos using CRISPR/Cas9 and cytosine base editors: toward a model of congenital deafness

Abstract

Mutations in the GJB2 gene, which encodes Connexin 26 (Cx26), are responsible for the majority of cases of non-syndromic congenital hearing loss in humans. While murine GJB2 knockout models have provided mechanistic insight, anatomical and physiological differences limit their translational relevance. Pigs represent a valuable large-animal model because their auditory anatomy and maturation closely resemble those of humans. This study compared two genome-editing approaches to disrupt GJB2 in porcine oocytes before fertilization: (1) electroporation with CRISPR/Cas9 ribonucleoprotein and (2) microinjection with cytosine base editor (BE3) and single-guide RNAs (sgRNAs). Electroporation produced high mutation rates (70-90%) across three concentrations of Cas9/sgRNA but yielded mostly heterozygous or mosaic blastocysts, with limited homozygous knockouts (< 4%). BE3 achieved precise cytosine-to-thymine conversions that introduced premature stop codons, reaching up to 47% total editing and 20% homozygous nonsense alleles. However, blastocyst formation declined at higher component concentrations. Overall, BE3 produced more predictable mutations than conventional CRISPR/Cas9, although embryo developmental competence was dose-dependent. Both methods effectively targeted GJB2 and demonstrated feasibility of pre-fertilization genome editing in porcine oocytes. These findings establish the groundwork for generating GJB2-deficient pigs as translational models of Cx26-related congenital deafness and for future evaluation of gene-therapy strategies in a large-animal system.