Generation of pigs with humanized type II collagen by precise human COL2A1 gene knock-in.

Osteoarthritis(OA)is the most common chronic disease,charac-terized by progressive cartilage breakdown,subchondral bone scle-rosis,and aberrant bone outgrowth(Yucesoy et al.,2015;Hussain et al.,2016).OA is one of the leading causes of cartilage damage.Pa-tients with severe cartilage damage require transplantation of artic-ular cartilage to improve their quality of life.Type Ⅱ collagen is a major component of articular cartilage and intervertebral discs and plays an important role in the structure and strength of connective tis-sues that support muscles and joints(Byers,1994).