H2BC21 and keratoconus: We used conditional Lox-Stop-Lox-(LSL)-KrasG12D and LSL-Cas9-GFP mice crossed to the pancreas-specific PDX1-Cre driver line (termed KC mice) and injected an adeno-associated virus that expresses a sgRNA and the H2B-RFP fluorescent marker (AAV-sgRNA-RFP) (Fig. 1a).