Subcellular targeting and function of osteoblast nucleotide pyrophosphatase phosphodiesterase 1

The ectonucleoside pyrophosphatase phosphodiesterase 1 (NPP1/PC-1) is a member of the NPP enzyme family that is critical in regulating mineralization. In certain mineralizing sites of bone and cartilage, membrane-limited vesicles [matrix vesicles (MVs)] provide a sheltered internal environment for nucleation of calcium-containing crystals, including hydroxyapatite. MV formation occurs by budding of vesicles from the plasma membrane of mineralizing cells. The MVs are enriched in proteins that promote mineralization. Paradoxically, NPP1, the type II transmembrane protein that generates the potent hydroxyapatite crystal growth inhibitor inorganic pyrophosphate (PP_i), is also enriched in MVs. Although osteoblasts express NPP1, NPP2, and NPP3, only NPP1 is enriched in MVs. Therefore, this study uses mineralizing human osteoblastic SaOS-2 cells, a panel of NPP1 mutants, and NPP1 chimeras with NPP3, which does not concentrate in MVs, to investigate how NPP1 preferentially targets to MVs. We demonstrated that a cytosolic dileucine motif (amino acids 49–50) was critical in localizing NPP1 to regions of the plasma membrane that budded off into MVs. Moreover, transposition of the NPP1 cytoplasmic dileucine motif and flanking region (AAASLLAP) to NPP3 conferred to NPP3 the ability to target to the plasma membrane and, subsequently, concentrate in MVs. Functionally, the cytosolic tail dileucine motif NPP1 mutants lost the ability to support MV PP_i concentrations and to suppress calcification. The results identify a specific targeting motif in the NPP1 cytosolic tail that delivers PP_i-generating NPP activity to osteoblast MVs for control of calcification. calcification; dileucine motif; NPP3     

Thesaurus-based disambiguation of gene symbols

Background  

Massive text mining of the biological literature holds great promise of relating disparate information and discovering new knowledge. However, disambiguation of gene symbols is a major bottleneck.     

Functional studies of signaling pathways in peri-implantation development of the mouse embryo by RNAi

Background

Studies of gene function in the mouse have relied mainly on gene targeting via homologous recombination. However, this approach is difficult to apply in specific windows of time, and to simultaneously knock-down multiple genes. Here we report an efficient method for dsRNA-mediated gene silencing in late cleavage-stage mouse embryos that permits examination of phenotypes at post-implantation stages.

Results

We show that introduction of Bmp4 dsRNA into intact blastocysts by electroporation recapitulates the genetic Bmp4 null phenotype at gastrulation. It also reveals a novel role for Bmp4 in the regulation the anterior visceral endoderm specific gene expression and its positioning. We also show that RNAi can be used to simultaneously target several genes. When applied to the three murine isoforms of Dishevelled, it leads to earlier defects than previously observed in double knock-outs. These include severe delays in post-implantation development and defects in the anterior midline and neural folds at headfold stages.

Conclusion

Our results indicate that the BMP4 signalling pathway contributes to the development of the anterior visceral endoderm, and reveal an early functional redundancy between the products of the murine Dishevelled genes. The proposed approach constitutes a powerful tool to screen the functions of genes that govern the development of the mouse embryo.     

The murine plasma cell antigen PC-1: purification and partial amino acid sequence

The murine plasma cell alloantigen PC-1 is selectively expressed on B lymphocytes in their terminal phase of differentiation into antibody-secreting cells. Previous work on an analytical scale has shown that PC-1 consists of two apparently identical disulfide-bonded polypeptides, each of Mr 115,000. In this paper, we describe the generation of a monoclonal antibody to PC-1 and its use in the preparative isolation of PC-1 by affinity chromatography. Final purification to apparent homogeneity was achieved by preparative polyacrylamide gel electrophoresis. It was estimated that NS-1 myeloma cells possess 1 to 4 X 10(5) PC-1 monomers per cell on their surface. The yield of PC-1 after purification was approximately 10(5) monomers per cell. Purified PC-1 was digested with trypsin, and the resulting peptides were separated by reversed-phase high-performance liquid chromatography. Purified peptides were sequenced with a gas-phase sequencer.