Migration linked to FUCCI-indicated cell cycle is controlled by PTH and mechanical stress.

Bone metabolism is maintained via balanced repetition of bone resorption by osteoclasts and bone formation by osteoblasts. Osteoblastic cells are capable of conducting self-renewal and differentiation that are basically associated with cell-cycle transition to enable cell specification and bone formation. Osteoblasts are also migrating to fill the resorption cavity curved by osteoclasts during bone remodeling to maintain homeostasis of bone mass whose imbalance leads to osteoporosis. However, technical difficulties have hampered the research on the dynamic relationship between cell cycle and migration in osteoblasts. In this report, we overcome these problems by introducing fluorescent ubiquitination-based cell cycle indicator (FUCCI) reporter system in calvarial osteoblastic cells and reveal that the cells in G1 as well as S/G2 /M phase are migrating. Furthermore, the osteoblastic cells in S/G2 /M phase migrate faster than those in G1 phase. Interestingly, parathyroid hormone (PTH) as an anabolic agent enhances migration velocity of the cells. Mechanical stress, another anabolic signal, also enhances migration velocity. In contrast, in the presence of both PTH and mechanical stress, the migration velocity returns to the base line levels revealing the interaction between the two anabolic stimuli in the regulation of cell migration. Importantly, PTH and mechanical stress also interact when they regulate the transition of cell cycle. These data demonstrate that osteoblastic migration is linked to cell cycle and it is under the control of mechanical and chemical stimuli that coordinate to regulate bone mass.