Nearly every extracellular ligand that has been found to play a role in regulating bone biology acts, at least in part, through MAPK pathways. Nevertheless, much remains to be learned about the contribution of MAPKs to osteoblast biology in vivo. Here we report that the p38 MAPK pathway is required for normal skeletogenesis in mice, as mice with deletion of any of the MAPK pathway member-encoding genes MAPK kinase 3 (Mkk3), Mkk6, p38a, or p38b displayed profoundly reduced bone mass secondary to defective osteoblast differentiation. Among the MAPK kinase kinase (MAP3K) family, we identified TGF-β-activated kinase 1 (TAK1; also known as MAP3K7) as the critical activator upstream of p38 in osteoblasts. Osteoblast-specific deletion of Tak1 resulted in clavicular hypoplasia and delayed fontanelle fusion, a phenotype similar to the cleidocranial dysplasia observed in humans haploinsufficient for the transcription factor runt-related transcription factor 2 (Runx2). Mechanistic analysis revealed that the TAK1-MKK3/6-p38 MAPK axis phosphorylated Runx2, promoting its association with the coactivator CREB-binding protein (CBP), which was required to regulate osteoblast genetic programs. These findings reveal an in vivo function for p38β and establish that MAPK signaling is essential for bone formation in vivo. These results also suggest that selective p38β agonists may represent attractive therapeutic agents to prevent bone loss associated with osteoporosis and aging.

The influence of signals transmitted by the phosphatase calcineurin and the transcription factor NFAT on the development and function of natural killer T (NKT) cells is unclear. In this report, we demonstrate that the transcription factor early growth response 2 (Egr2), a target gene of NFAT, was specifically required for the ontogeny of NKT cells but not that of conventional CD4 + or CD8 + T cells. NKT cells developed normally in the absence of Egr1 or Egr3, which suggests that Egr2 is a specific regulator of NKT cell differentiation. We found that Egr2 was important in the selection, survival and maturation of NKT cells. Our findings emphasize the importance of the calcineurin-NFAT-Egr2 pathway in the development of the NKT lymphocyte lineage.Mouse natural killer T (NKT) cells that express an invariant T cell antigen receptor (TCR) α-chain composed of variable α-chain region 14 (V α 14) and joining α-chain region 18 (J α 18) gene segments (V α 14i) constitute a distinct lymphocyte subset that coexpresses TCRαβ and markers of the NK cell lineage. NKT cells function in the first line of defense against infectious agents, contribute to the development of asthma and chronic obstructive pulmonary disease, potently promote the regression of transplanted tumors, and influence the maintenance of immunological tolerance 1-3 . Unlike conventional T lymphocytes, which express a diverse repertoire of TCRα and TCRβ, NKT cells combine the V α 14i TCRα chain (V α 24-J α 18 in humans) with a restricted repertoire of TCRβ proteins that contain V β 8, V β 7 or V β 2 segments (V β 11 in humans). Also in contrast to conventional T lymphocytes, which recognize peptides bound to major histocompatibility complex molecules and are selected by thymic stromal cells that present complexes of peptide and major histocompatibility complex, NKT cells are

Formation and remodeling of the skeleton relies on precise temporal and spatial regulation of genes expressed in cartilage and bone cells. Debilitating diseases of the skeletal system occur when mutations arise that disrupt these intricate genetic regulatory programs. Here, we report that mice bearing parallel null mutations in the adapter proteins Schnurri2 (Shn2) and Schnurri3 (Shn3) exhibit defects in patterning of the axial skeleton during embryogenesis. Postnatally, these compound mutant mice develop a unique osteochondrodysplasia. The deletion of Shn2 and Shn3 impairs growth plate maturation during endochondral ossification but simultaneously results in massively elevated trabecular bone formation. Hence, growth plate maturation and bone formation can be uncoupled under certain circumstances. These unexpected findings demonstrate that both unique and redundant functions reside in the Schnurri protein family that are required for proper skeletal patterning and remodeling.chondrodysplasia | osteoblast | skeletogenesis

The genomic promoter of human parainfluenza virus type 3 (HPIV3) contains multiple cis-elements controlling transcription and replication. Previous work showed that regions 1 to 12 and 79 to 96 were critical in promoting replication of an HPIV3 minireplicon, while the intergenic sequence and N gene start signal (IS/Ngs, bases 49 to 61) were important for transcription. Because these data were collected primarily using point mutations, not every base from position 1 to 96 was analyzed, and some important control elements may have been missed. To clarify the role of bases 13 to 78 in transcription and replication, a series of mutations were made which collectively scanned this entire region. Mutation of bases 13 to 28 resulted in markedly decreased HPIV3 minireplicon replication, indicating these bases constitute an additional cis-element involved in the synthesis of the HPIV3 antigenomic RNA. The position dependence of the IS/Ngs was also examined. Analysis of mutants in which the IS/Ngs was shifted 5 or 3 showed that this segment could be moved without significantly disrupting transcription initiation. Additional mutants which contained two successive IS/Ngs segments were created to test whether the polymerase accessed the gene start signal by proceeding along the template 3 to 5 or by binding internally at the gene start signal. Based on analysis of the double gene start mutants, we propose a model of internal transcription initiation in which the polymerase enters the template at approximately the location of the natural N gene start but then scans the template bidirectionally to find a gene start signal and initiate transcription.Human parainfluenza virus type 3 (HPIV3) is an enveloped, nonsegmented, negative-sense RNA virus within the Respirovirus genus of the subfamily Paramyxovirinae, family Paramyxoviridae, order Mononegavirales. HPIV3 is an important cause of lower respiratory tract infections in young children and is being increasingly recognized as a cause of serious lower respiratory tract infections in the immunocompromised and elderly (4,14,15,35).During replication of the mononegaviruses, the nucleocapsid (N) protein-encapsidated genomic and antigenomic RNAs serve as templates for the synthesis of cRNA. Specific factors affecting RNA replication vary among the different families and subfamilies of the Mononegavirales. For the Paramyxovirinae, which includes the Respirovirus (HPIV3 and Sendai virus [SeV]), Morbillivirus (measles virus), and Rubulavirus (simian virus 5 [SV5]) genera, these factors include a requirement for specific sequence elements at the 3Ј ends of the genome and antigenome, proper spacing between sequence elements, and adherence to the rule of six (20,39).The genomic and antigenomic promoters (the 3Ј ends of the genome and antigenome; GP and AGP, respectively) of all members of the Paramyxovirinae studied thus far contain two critical regions: conserved region I (CRI) and conserved region II (CRII) (16,22,24,26,33,34,38). Conserved region I is at the extreme 3Ј end of the genomic ...