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Rodent hindlimb unloading (HU) by tail-suspension is a model to investigate disuse-induced bone loss in vivo. Previously, we have shown that osteopontin (OPN, also known as Spp1) is required for unloading-induced bone loss. However, how unloading affects OPN expression in the body is not fully understood. Here, we examined OPN expression in peripheral blood of mice subjected to HU. Real-time RT-PCR analysis indicated that OPN expression is increased in circulating peripheral blood cells. This HU-induced increase in OPN mRNA expression was specific in circulating peripheral blood cells, as OPN was not increased in the blood cells in bone marrow. HU-induced enhancement in OPN expression in peripheral blood cells was associated with an increase in the fraction of monocyte/macrophage lineage cells in the peripheral blood. In contrast, HU decreased the fraction size of B-lymphocytes in the peripheral blood. We further examined if B-lymphogenesis is affected in the mice deficient for osteopontin subjected to HU. In bone marrow, HU decreased the population of the B-lymphocyte lineage cells significantly, whereas it did not alter the population of monocyte/macrophage lineage cells. HU also increased the cells in T-lymphocyte lineage in bone marrow. Interestingly, these changes were observed similarly both in OPN-deficient and wild-type mice. These results indicate for the first time that HU increases OPN expression in circulating cells and suppresses bone marrow B-lymphogenesis.

We report here the cloning and expression of the Xenopus orthologue of the T-box transcription factor gene Tbx2 (optomotor-blind in Drosophila). Tbx2 is first detected in the ventral mesodermal cells just above the yolk plug at late gastrula. At the neurula stage it is strongly expressed in the cement gland, dorsal root ganglia, and otic vesicle region. At the tailbud stage strong Tbx2 expression is observed in the dorsal part of the optic cup and trigeminal ganglia, and it is also expressed in the branchial arches, heart anlage, nasal pit, proctodeum, and the region around the pronephros.