Bone development: overview of bone cells and signaling.

Vertebrates evolved elaborating a structure made up of more than 200 bones and cartilages articulated with one another to form the skeleton, through which locomotion, organ protection, lodging of hematopoiesis, and mineral homeostasis are allowed. Skeletogenesis starts at the fetal stage, along with marrow hematopoiesis, and evolves postnatally through modeling and remodeling processes that permit skeletal mass buildup. Preservation of skeletal mass is then implemented by balanced remodeling, which ensures continuous renovation of the tissue to allow its mechanical, structural, and metabolic properties to remain unaltered until ageing or diseases disrupt this equilibrium. Skeletal homeostasis is fulfilled by specialized bone cells in association with systemic and local regulators. Herein I review landmark discoveries that shed light on the intricate mesh connecting bone cells among themselves and with other systems, thus representing the cellular basis of normal and abnormal bone development and homeostasis.