Cartilage plays an important role in mechanical load resistance and in skeletal structure support. It also serves as the skeletal template for endochondral ossification by which most bones in the body, such as long bones, are formed. In endochondral ossification, cartilage development is initiated by mesenchymal cell condensation, followed by a series of proliferation and differentiation processes. Cells undergoing condensation differentiate into chondrocytes, which then proliferate, produce type II collagen and form the proliferative zone of the cartilage molds. As development proceeds, chondrocytes in the center of the cartilage molds (prehypertrophic zone) cease proliferating and differentiate into type X collagen-producing hypertrophic chondrocytes to form the hypertrophic zone. Terminally differentiated hypertrophic chondrocytes mineralize the surrounding matrix. Eventually these cells die by apoptosis and are replaced by osteoblasts that form trabecular bone.The regulation of chondrocyte proliferation and differentiation must be tightly coordinated to allow formation of properly sized cartilage and bone (1). Parathyroid hormone-related peptide (PTHrP) 2 and parathyroid hormone (PTH) sustain chondrocyte proliferation and delay differentiation of the growth plate (2). PTHrP is expressed by perichondrial cells and chondrocytes in the upper region of growing cartilage. Mutant mice that are deficient in PTHrP (3), PTH (4), or its receptor (5) have short proliferative zones and accelerated chondrocyte differentiation, which results in abnormal endochondral bone formation. In contrast, mice that overexpress PTHrP have enlarged proliferative zones and delayed chondrocyte terminal differentiation (6). Humans with an activating mutation in the PTH/ PTHrP receptor develop Jansen metaphyseal chondrodysplasia, characterized by disorganization of the growth plates and delayed chondrocyte terminal differentiation (7). These results suggest that PTH/PTHrP signaling regulates skeletal development by promoting cell proliferation and inhibiting hypertrophic differentiation of chondrocytes.The binding of PTH/PTHrP to its receptor activates both G s and G q family heterotrimeric G proteins (8, 9). The activation of G s is necessary for cAMP production and protein kinase A (PKA) activation, which leads to phosphorylation of the cAMPresponse element-binding (CREB) family of transcription factors. CREB then induces genes such as the cyclin D1 and cyclin A genes. The activated cyclin/cyclin-dependent kinases in turn phosphorylate the retinoblastoma protein and its relative factors, which then dissociates the E2F transcription factor and subsequently activates the target genes necessary for DNA replication and cell cycle progression. Thus, CREB is a direct target of PKA and a downstream target of PTH/PTHrP/cAMP signaling and is required for chondrocyte proliferation (10, 11). How proliferation signaling is down-regulated in the prehypertrophic zone to stop proliferation and allow the switch to the postmitotic state is not well unde...

Pannexin 3 functions as an essential protein for Ca2+ and ATP transport and cell–cell communication during osteoblast differentiation

Background:The role of dental epithelium in stem cell differentiation has not been clearly elucidated. Results: SP cells differentiated into odontoblasts by epithelial BMP4, whereas iPS cells differentiated into ameloblasts when cultured with dental epithelium. Conclusion: Stem cells can be induced to odontogenic cell fates when co-cultured with dental epithelium. Significance: This is the first report to show induction of ameloblasts from iPS cells.

TGF-β has been implicated in the proliferation and differentiation of chondrocytes and osteoblasts. However, the in vivo function of TGF-β in skeletal development is unclear. In this study, we investigated the role of TGF-β signaling in growth plate development by creating mice with a conditional knockout of the TGF-β type I receptor ALK5 (ALK5CKOCKO) in skeletal progenitor cells using Dermo1-Cre mice. ALK5CKO mice had short and wide long bones, reduced bone collars, and trabecular bones. In ALK5CKO growth plates, chondrocytes proliferated and differentiated, but ectopic cartilaginous tissues protruded into the perichondrium. In normal growth plates, ALK5 protein was strongly expressed in perichondrial progenitor cells for osteoblasts, and in a thin chondrocyte layer located adjacent to the perichondrium in the peripheral cartilage. ALK5CKO growth plates had an abnormally thin perichondrial cell layer and reduced proliferation and differentiation of osteoblasts. These defects in the perichondrium likely caused the short bones and ectopic cartilaginous protrusions. Using tamoxifen-inducible Cre-ER™-mediated ALK5-deficient primary calvarial cell cultures, we found that TGF-β signaling promoted osteoprogenitor proliferation, early differentiation, and commitment to the osteoblastic lineage through the selective MAPKs and Smad2/3 pathways. These results demonstrate the important roles of TGF-β signaling in perichondrium formation and differentiation, as well as in growth plate integrity during skeletal development.

Autoimmune thyroid disease (AITD) is caused by an immune response to self-thyroid antigens and has a significant genetic component. Antisense RNA transcripts have been implicated in gene regulation. Here we have identified a novel zinc-finger gene, designated ZFAT (zinc-finger gene in AITD susceptibility region), as one of the susceptibility genes in 8q23-q24 through an initial association analysis using the probands in the previous linkage analysis and a subsequent association analysis of the samples from a total of 515 affected individuals and 526 controls. The T allele of the single-nucleotide polymorphism (SNP), Ex9b-SNP10 located in the intron 9 of ZFAT, is associated with increased risk for AITD (dominant model: odds ratio = 1.7, P = 0.000091). The Ex9b-SNP10 falls into the 3'-UTR of truncated-ZFAT (TR-ZFAT) and the promoter region of the small antisense transcript of ZFAT (SAS-ZFAT). In peripheral blood lymphocytes, SAS-ZFAT is exclusively expressed in CD19+ B cells and expression levels of SAS-ZFAT and TR-ZFAT seemed to correlate with the Ex9b-SNP10-T-associated ZFAT-allele, inversely and positively, respectively. The Ex9b-SNP10 is critically involved in the regulation of SAS-ZFAT expression in vitro and this expression results in a decreased expression of TR-ZFAT. These results suggested that the SNP-associated ZFAT-allele plays a critical role in B cell function by affecting the expression level of TR-ZFAT through regulating SAS-ZFAT expression and that this novel regulatory mechanism of SNPs might be involved in controlling susceptibility or resistance to human disease.

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The molecular mechanisms by which TGF-β and interleukin 4 (IL-4) signaling control the differentiation of IL-9-producing CD4+ T (TH9) cells remain incompletely understood. We show here that the DNA-binding inhibitor Id3 regulated Th9 cell differentiation, as deletion of Id3 increased IL-9 production from CD4+ T cells. Mechanistically, TGF-β1 and IL-4 down-regulated Id3 expression and this process required the kinase TAK1. Reduction of Id3 expression enhanced the binding of the transcription factors E2A and GATA-3 in the Il9 promoter region, which promoted Il9 gene transcription. Importantly, Id3 control of TH9 cells differentiation regulated anti-tumor immunity in an experimental melanoma-bearing model in vivo, and also in human CD4+ T cells in vitro. Thus, this study reveals a previously unrecognized TAK1-Id3-E2A-GATA-3 pathway that regulates TH9 cell differentiation.

Background:The mechanism of the transition from osteoprogenitor cell proliferation to differentiation is unclear. Results: Panx3 inhibits osteoprogenitor proliferation by blocking canonical Wnt signaling and promoting p21 activation. Conclusion: A Panx3 hemichannel induces multiple Panx3 signaling pathways critical for the cell cycle exit. Significance: Our findings reveal that Panx3 is a new regulator to switch the stage from proliferation to differentiation in osteoprogenitor cells.