Understanding early human knee joint development with a single cell RNAseq approach

Mature synovial joints consist of cruciate ligament, articular cartilage, superficial membrane and mensicus. During limb development, all these structures are developed from a transient joint anlagen called the interzone. Studies in mouse are relatively well established but less imformation is available for human joint. This study captured progenitors and committed joint and surrounding growth plate cartilage from 4 human fetuses (from 9w to 18wk gestation time). Skin, muscles and surrounding soft tissues (inlcuding patella, patella tendon and collacteral ligaments) were removed from the collected fetal knee joints (with minimal growth plate tissues). Tissues were digested to single cell with collagenase P and sent for 10x genomics encapsulation. These 4 samples covered stages of early joint lineage committment (9w) to lineage maturation (18w). Progenitors and committed cells in cruciate ligament, articular cartilage, superficial zone, and meniscus were captured in these dataset. As meniscus is a fibrocartilage structure, one horn of mensicus was dissected and sequenced seperately (h18WMC), and the remaining parts of the joint was sequenced as h18WKJ.