Cell transplantation has recently been attempted to improve musculoskeletal function. Many types of cells, such as embryonic stem cells, fetal cardiomyocytes, myoblasts, bone marrow hematopoietic cells, and mesenchymal stem cells (MSCs), have been transplanted to functionally restore damaged or diseased tissue in animal models, and marrow-derived mononuclear cells have been injected into ischemic limb clinically. MSCs can be a useful source of cell transplantation for several reasons:they have the ability to proliferate and differentiate into mesodermal tissues, including myocytes, they entail no ethical or immunological problems, and bone marrow aspiration is an established routine procedure. When placed in appropriate in vitro and in vivo environments, MSCs can give rise to all major mesenchymal tissues, such as bone, cartilage, muscle, and adipose tissue. Direct injection of murine and porcine MSCs into skeletal muscles has been shown to be feasible in murine models of ischemic limb. Large numbers of cells must be injected into damaged sites in ischemic limb to restore muscular function in humans, and cells need to be injected into the entire limb. Until now, however, there have been no reports of a sufficient number of differentiated human myocytes ever having been obtained to restore muscular function of ischemic limb. One of the reasons for this is that the life span of human cells in vitro is limited. Human cells reach senescence or stop cell growth after a limited number of cell replications, and the average number of hMSC population doublings (PDs) has been found to be 38, implying that it would be difficult to obtain enough cells to restore the function of ischemic limb. To resolve these problems and to establish a model of cell-based therapy, prolongation of the life span of hMSCs without affecting differentiation capability is essential.

Osteoblasts are derived from mesenchymal stem cells, common progenitors for adipocytes and other lineages. While transcription factors such as Runx2/Cbfa1 and Osterix are absolutely required for osteoblast differentiation, simply increasing their expression does not necessarily lead to increased bone formation. In contrast, genes such as deltafosB and an AP-1 target, interleukin-11, which have been shown to enhance bone formation in vivo and to be induced by mechanical stress and PTH, can be better therapeutic targets to develop drugs that stimulate bone formation.

Taste buds, the sensory end organs for the sense of taste, consist of taste sensing cells, supportive cells and basel cells. Taste bud cells are heterogeneous in terms of morphology as well as functional profiles. Although the lineage of mammalian taste bud cells is largely unknown, it is generally accepted that undifferentiated epithelial basal cells surrounding taste buds enter the taste buds to form and maintain this specialized corpuscle. To analyze taste bud formation during development, we conducted morphological observations and examined differentiation marker expression. Thickening of epithelia starts at 13 dpc foetus and immunohistochemistry against a neural marker, PGP 9.5, revealed that the change of epithelial morphology precedes neural projection observed at 14 dpc foetus. Taste sensing cells appear 6 days after birth indicated by expression of the single transduction component phospholipase Cbeta2 (PLCbeta2) as differentiation marker. To further investigate the maintenance and cell lineage in the taste buds in adults, we injected 5'bromo-2'deoxyuridine (BrdU) solution to young growing mice for a week. BrdU label retaining cells (LRCs) could be observed even 8 weeks after injection. LRCs were examined the differentiation by PLCbeta2 and proliferative activity by Ki-67. The results suggested two possibilities. (1) Part of PLCbeta2 positive cells retain proliferative activity and multipotentiality, or (2) precursor cells (stem cells) stay in the taste buds and produce at least part of the taste sensing cells through proliferation and differentiation processes.

In the present study, the molecular mechanisms regulating p 21(WAF1/CiP1) expression by basic helix-loop-helix (bHLH) factors during cellular differentiation were investigated. The cyclin dependent kinase inhibitor p 21 plays crucial roles during differentiation of osteoblasts and myoblasts. In the osteoblastic cell line MG 63, expression of the p 21 gene has been shown to be upregulated by E2A factors, members of the bHLH factor family. In addition, E2A-dependent activation of p21 promoter can be inhibited by another bHLH factor, TWIST. Using reporter assays with mutant p 21 promoters, a novel element was identified in the p21 promoter, which is essential for E2A-dependent activation and TWIST-mediated inhibition. Interestingly, in the myoblastic cell line C2C12, this sequence was not involved in E2A-dependent activation of p21 expression. Gel mobility shift assays showed a specific complex of the novel p21 promoter element with nuclear factor(s) of MG 63 cells. Complex formation was inhibited by the addition of anti-TWIST antibody. In contrast no complexes could be identified with C2C12 cells. These results raise the possibility that interactions of the bHLH factors with the novel p21 promoter element are cell type specific. This suggests a novel mechanism regulating p 21 expression.

Bone is a complex tissue which contains osteoclasts, osteoblasts, chondrocytes, adipocytes, hematopoietic cells and immune cells. Since osteoblasts share the same origin with adipocytes in bone marrow cavity, it is assumed that PPAR (peroxisome proliferator-activated receptor) family, which is an important nuclear receptor family for adipocyte differentiation, plays a role in the bone microenvironment. Indeed, recent evidences support the primitive roles of PPAR family in osteoblast differentiation as well as adipocyte differentiation. Furthermore, PPAR family is also implicated in the regulation of differentiation and function of osteoclasts. Here, we summarized the functional roles of PPAR family in bone remodeling and regulation of bone microenvironments. We also discuss the potential mechanisms that regulate expression and function of PPAR family during bone metabolisms.

We established clonal cell lines from fetal brains and a cerebellum of p53 deficient mice. In this paper, stem cell lines are selectively described. FBD-103a line generates neurons, astrocytes and oligodendrocytes. 2Y-6fl line generates neurons and astrocytes. 2Y-3t line generates neurons and oligodendrocytes. FBD-104 line generates astrocytes in conventional culture, but formation of spheres in suspension culture gives the line the capability to produce neurons in addition to astrocytes. Analyses of these lines were done mainly by limited dilution cloning, immunostaining and Western blotting. Some factors in culture medium and kidney were shown to regulate differentiation of the stem cell lines.