Sam68 protein expression was observed throughout the developing mouse embryo, in keeping with previous reports that identified the Sam68 mRNA to be widely expressed [38]. We observe Sam68 staining in the brain, heart, and intestine (see Figure 1) as well as liver, skin, and kidney (unpublished data) of late-stage embryos. This expression pattern is consistent with previous work that has observed Sam68 in neurons [52] and as a substrate of the intestinal SIK/breast tumor kinase [43]. The expression of Sam68 was not altered in aging bone marrow stromal cells or in senescencing WI-38 cells (unpublished data). The presence of Sam68 in chondrocytes, osteoblasts and osteoclasts in developing cartilage and bone predicted a pivotal role for the protein in skeletal development.