Viability-Based Assessment Reveals True Efficiency of CRISPR-Cas9 Transfection Methods in Rabbit Spermatozoa

Modern genome editing tools such as CRISPR-Cas9 have revolutionized mammalian genome engineering, yet translation to in vivo applications remains limited by low efficiency and frequent occurrence of mosaicism. Sperm-mediated delivery of editing reagents is one proposed alternative that may mitigate these issues. This method depends on efficient transfection of genome editing materials into viable spermatozoa, a critical yet frequently overlooked parameter. Using FACS, we compared electroporation (Neon NxT) and lipofection (CRISPRMAX) for introducing CRISPR-Cas9 ribonucleoproteins into viable rabbit spermatozoa. Electroporation, shown to enable Cas9 and plasmid transfection in spermatozoa from other species, performed poorly once dead spermatozoa were excluded. In contrast, Lipofectamine CRISPRMAX improved transfection efficiency with minimal effects on spermatozoa viability and motility. These findings emphasize the importance of distinguishing true transfection (transfection of viable spermatozoa) from total transfection and highlight lipofection as a promising alternative to electroporation for sperm-based genome editing, with potential applications in rabbit genome engineering.