Bone Appétit! The Skeletal SystemOlivierPourquié2009Cold Spring Harbor Laboratory PressCold Spring Harbor, NY, USA365 pp. $95.00

Not long ago, the skeleton was viewed as a mere supporting structure appealing only to a small group of specialists. Research in the past two decades, however , has revealed marvelous intricacies concerning the formation and remod-eling of the skeleton, its intimate connections with other organs in the body, and elegant genetic circuitries that regulate skeletal cell differentiation. These new revelations have not only energized those studying skeletal biology but have also attracted interest from other investigators. Therefore, a book encapsulating the current state of skeletal biology would benefit both veterans in the field and newcomers alike. The Skeletal System, edited by Olivier Pourquie and written by leading experts in the field, aspires to do just that. The thirteen-chapter book places a clear focus on embryonic development of the vertebrate skeleton, an area that boasts most of the recent advances. Chapters 2–4 are devoted to skeletal patterning, which has long fascinated embryol-ogists and developmental biologists who are interested in deciphering the rules for specific pattern formation. Although classical embryologi-cal experiments are credited with uncovering many of the ground rules of skeletal development, it is the modern molecular and genetic techniques that have revealed the identities of the key regulators. These chapters recount in detail the growth factors (such as Wnt, fibroblast growth factor, and sonic hedgehog) and transcription factors (such as the Hox family) that play critical roles in patterning the limb (Chapter 2 by Cooper and Tabin), the axial (Chapter 3 by Chal and Pourquié), and the craniofacial skeletons (Chapter 4 by Le Douarin and Creuzet). A future challenge is to determine how extracellu-lar signals are integrated with the activity of transcription factors, and how these signals are translated into positional information and unique morphogenetic events that ultimately determine skeletal patterns. Perhaps the most impressive advances in recent years have come from studies of the molecular mechanisms governing the differentiation of skeletal cell types, including chondrocytes (which produce cartilage), osteoblasts (bone-forming cells), and osteoclasts (which resorb bone). These advances, covered in Chapters 5–9, range from cytokines controlling osteoclast formation to transcription factors and growth factors that regulate chondrocyte and osteoblast differentiation. Whereas osteoclasts belong to the hematopoietic lineage, osteoblasts and chondrocytes are thought to develop from a common mesenchymal progenitor of either mesodermal or neural crest origin. In support of this notion, cell fate " switching " is observed in mutant mice in which either osteoblast or chondrocyte differentiation …