Figure 1. Developmental origins of different connective tissues that have been reported to contain “MSCs”. Of note, bone originates from three different embryonic specifications (noted by a white star). Skin, muscle, tendons and ligaments, and bone arise from different specifications of the sclerotome. Bone marrow adipose tissue originates from paraxial mesoderm, lateral plate mesoderm and neural crest. While bone marrow adipose tissue arises from mesoderm and neural crest, other forms of fat originate from all three germ layers. “MSCs” are not a lineage. MSC: mesenchymal stem/stromal cell. Adapted from Bianco and Robey.².