Cover photograph (Copyright © 2007, American Society for Microbiology. All Rights Reserved.): Various assays surround the mouse. Primary mouse embryo fibroblasts grown in micromass culture have been induced to commit into the chondrogenic lineage by the addition of BMP2. Chondrogenic maturation was followed by alcian blue and alkaline phosphatase staining (upper right), and protein and RNA were prepared for molecular analysis (lower left). Skeletal elements were isolated from neonatal and embryonic animals. Alcian blue and alizarin red were used to monitor endochondral ossification (upper left), and gene expression was monitored by in situ hybridization (lower right). (See related article on p. 5161.)