The parathyroid hormone-related peptide (PTHrP) gene was disrupted in murine embryonic stem cells by homologous recombination, and the null allele was introduced into the mouse germ line. Mice homozygous for the PTHrP null mutation died postnatally, probably from asphyxia, and exhibited widespread abnormalities of endochondral bone development. Histological examination revealed a diminution of chondrocyte proliferation, associated with premature maturation of chondrocytes and accelerated bone formation. Analysis of earlier developmental stages revealed that disturbance in cartilage growth preceded abnormal endochondral bone formation. There were no morphological abnormalities apparent in other tissues. These results provide direct evidence implicating PTHrP in normal skeletal development and serve to emphasize its potential involvement in human osteochondrodysplasias.

(FcR γ-chain), the non-receptor tyrosine kinase Syk and Bristol BS8 1TD, UK phospholipase Cγ2 (PLCγ2) (Blake et al., 1994; Daniel et al., 1994a; Fujii et al., 1994;Yanaga et al., 1995; 5 Corresponding author Asazuma et al., 1996;Gibbins et al., 1996). Syk assembles A.Poole, J.M.Gibbins and M.Turner contributed equally to this work into signalling complexes at the plasma membrane via interaction between its tandem Src homology 2 (SH2) Activation of mouse platelets by collagen is associated domains and a tyrosine-phosphorylated immunoreceptor with tyrosine phosphorylation of multiple proteins tyrosine-based activation motif (ITAM). We recently proincluding the Fc receptor γ-chain, the tyrosine kinase posed a model for collagen-induced signalling in human Syk and phospholipase Cγ2, suggesting that collagen platelets in which receptor clustering induced by collagen signals in a manner similar to that of immune receptors.leads to tyrosine phosphorylation of the FcR γ-chain, This hypothesis has been tested using platelets from possibly by a Src family kinase, allowing binding of Syk, mice lacking the Fc receptor γ-chain or Syk. Tyrosine which becomes tyrosine phosphorylated and activated phosphorylation of Syk and phospholipase Cγ2 by (Gibbins et al., 1996). This initiates a series of events collagen stimulation is absent in mice lacking the Fc which may involve other kinases and adapter proteins receptor γ-chain. Tyrosine phosphorylation of phospholeading to tyrosine phosphorylation and activation of lipase Cγ2 by collagen stimulation is also absent in mice PLCγ2. This model has been evaluated in the present platelets which lack Syk, although phosphorylation of study using platelets from genetically modified mice which the Fc receptor γ-chain is maintained. In contrast, lack the FcR γ-chain or Syk. tyrosine phosphorylation of platelet proteins by the G protein-coupled receptor agonist thrombin is maintained in mouse platelets deficient in Fc receptor Results γ-chain or Syk. The absence of Fc receptor γ-chain or Syk is accompanied by a loss of secretion and aggrega-Tyrosine phosphorylation in collagen-and tion responses in collagen-but not thrombin-stimulated thrombin-stimulated platelets platelets. These observations provide the first direct Collagen and thrombin stimulated distinct but overlapping evidence of an essential role for the immunoreceptor increases in whole cell tyrosine phosphorylation in platetyrosine-based activation motif (ITAM) in signalling lets (Figures 1 and 2A). Both agonists stimulated increases by a non-immune receptor stimulus.in tyrosine phosphorylation of proteins of~42, 70-75, Keywords: collagen/Fc receptor γ-chain/ITAM/platelets/ 100, 110 and 130 kDa in platelets from B6 mice; the 42 Syk and 110 kDa proteins were more heavily phosphorylated in thrombin-stimulated cells. The largest increase in tyrosine phosphorylation was in the 70-75 kDa proteins. Collagen but not thrombin also stimulated marked tyrosine phos-

Vav is a GTP͞GDP exchange factor (GEF) for members of the Rho-family of GTPases that is rapidly tyrosine-phosphorylated after engagement of the T cell receptor (

No abstract

Gaucher's disease is the most prevalent lysosomal storage disorder in humans and results from an autosomally inherited deficiency of the enzyme glucocerebrosidase (beta-D-glucosyl-N-acylsphingosine glucohydrolase), which is responsible for degrading the sphingolipid glucocerebroside. An animal model for Gaucher's disease would be important for investigating its phenotypic diversity and pathogenesis and for evaluating therapeutic approaches. A naturally occurring canine model has been reported but not propagated. Attempts to mimic the disease in animals by inhibiting glucocerebrosidase have been inadequate. Here we generate an animal model for Gaucher's disease by creating a null allele in embryonic stem cells through gene targeting and using these genetically modified cells to establish a mouse strain carrying the mutation. Mice homozygous for this mutation have less than 4% of normal glucocerebrosidase activity, die within twenty-four hours of birth and store glucocerebroside in lysosomes of cells of the reticuloendothelial system.

Dendritic cells (DCs) are the only APCs capable of initiating adaptive immune responses. The initiation of immune responses requires that DCs 1) internalize and present Ags; and 2) undergo a differentiation process, called “maturation”, which transforms DCs into efficient APCs. DC maturation may be initiated by the engagement of different surface receptors, including certain cytokine receptors (such as TNFR), Toll-like receptors, CD40, and FcRs. The early activation events that link receptor engagement and DC maturation are not well characterized. We found that FcR engagement by immune complexes induced the phosphorylation of Syk, a protein tyrosine kinase acting immediately downstream of FcRs. Syk was dispensable for DC differentiation in vitro and in vivo, but was strictly required for immune complexes internalization and subsequent Ag presentation to T lymphocytes. Importantly, Syk was also required for the induction of DC maturation and IL-12 production after FcR engagement, but not after engagement of other surface receptors, such as TNFR or Toll-like receptors. Therefore, protein tyrosine phosphorylation by Syk represents a novel pathway for the induction of DC maturation.

Key Points Question How does dementia status influence mortality in people with Down syndrome? Findings In a longitudinal study including 211 adults with Down syndrome 36 years and older, 27 people died during follow-up (mean, 28; range, 1-65 months), and dementia was the proximate cause of death in 70% of cases. Crude mortality rates were 5 times higher in those with dementia than those without. Meaning Nearly all older adults with Down syndrome now have dementia when they die, making this a vital population for researching disease progression, modifying factors, and potential treatments.

have a consensus binding site for the SH2 domain of Vav (DYESP) (2-5) and are heavily tyrosine-phosphorylated following TCR engagement, whereas Tyr 145 , which falls in the sequence DYEPP, is phosphorylated to a lesser extent (6). SLP-76 also contains a central proline-rich region that mediates the association with Grb2 (7) and a carboxyl-terminal SH2 domain that binds to at least two tyrosine-phosphorylated proteins, SLAP-130 (SLP-76-associated phosphoprotein of 130 kDa) (8), a 62-kDa protein, and an uncharacterized serine/threonine kinase after TCR engagement (7). SLP-76 is believed to be an essential adapter protein in T cells. Overexpression of SLP-76 results in an enhancement of TCR-mediated induction of nuclear factor of activated T cell and interleukin-2 promoter activity (3, 5-7, 9, 10). More recently, lack of expression of SLP-76 in Jurkat cells demonstrated that SLP-76 is necessary for tyrosine phosphorylation of phospholipase C-␥ 1 (PLC-␥ 1 ) and activation of the Ras pathway (11). Moreover, SLP-76 is required for normal thymocyte development, since SLP-76 knockout mice lack peripheral T cells (12, 13).The three tyrosine phosphorylation sites, the proline-rich region, and the SH2 domain of SLP-76 have all been shown to be important for the regulation of T cell interleukin 2 production (10). The inducible tyrosine phosphorylation of SLP-76 is mediated by ZAP-70 or Syk in COS cells (9) and rat basophilic leukemia cells (14), respectively. The mechanism by which SLP-76 is phosphorylated by ZAP-70 or Syk is not known.We have previously reported the association of tyrosinephosphorylated SLP-76 with the SH3 domain of Grb2 in platelets in response to stimulation of the low affinity IgG immunoreceptor Fc␥RIIA (15). Increasing evidence suggests that the collagen receptor underlying the major increase in tyrosine phosphorylation in platelets also signals like an immune receptor. The collagen receptor is believed to comprise a multimeric structure, containing the glycoprotein VI (GPVI), and the Fc receptor (FcR) ␥-chain (16 -19). Binding of collagen to GPVI induces tyrosine phosphorylation of the immunoreceptor tyrosine-based activation motif in the cytoplasmic tail of FcR ␥-chain (18), leading to tyrosine phosphorylation of Syk and