sentences:  Betacellulin stimulated the proliferation of retinal pigment epithelial and vascular smooth muscle cells at a concentration of [difference]30 pM (1 ng/ml) but did not stimulate the growth of several other cell types, such as endothelial cells and fetal lung fibroblasts.Betacellulin chemically bonds and activates tyrosine residues phosphorylation of the epidemic growth factor.Osteoblasts, which are responsible for forming and mineralizing osteoid, express EGF receptors and alter rates of proliferation and differentiation in response to EGF receptor activation.Transgenic mice over-expressing the EGF-like ligand betacellulin (BTC) exhibit increased cortical bone deposition; however, because the transgene is ubiquitously expressed in these mice, the identity of cells affected by BTC and responsible for increased cortical bone thickness remains unknown.