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Gene Review

SPP1  -  secreted phosphoprotein 1

Ovis aries

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Disease relevance of OPN


High impact information on OPN

  • The marker OarAE101 was linked to secreted phosphoprotein 1 (SPP1, which maps to chromosome 4q21-23 in man) in the test pedigrees and independent families (Zmax > 9.7) [3].
  • The geographic localization of cells expressing mRNA for alpha 1(I) procollagen, ALP, OP, and BGP implies subspecialization of osteoblasts in bone formation [4].
  • Similarly, only a proportion of cuboidal cells expressed OP mRNA early in bone formation, but the number of cells expressing OP mRNA increased with time [4].
  • The spindle-shaped cells in the granulation tissue expressed mRNA for alpha 1(I) procollagen, ALP, and OP but not BGP, suggesting that they may be osteoblast precursor cells. alpha 1(I) procollagen mRNA was strongly expressed by all cells on the surface of bone, with a peak intensity at 3W and then reducing sharply by 6W [4].
  • The temporal and spatial distribution of osteoblast gene markers was examined by in situ hybridization with nonradioactive digoxigenin probes for alpha 1(I) procollagen, alkaline phosphatase (ALP), osteopontin (OP), and bone Gla protein (BGP) [4].

Biological context of OPN

  • Secreted OPN is then available as ligand for alpha(v)beta(3) integrin heterodimer on trophectoderm and uterus to 1) stimulate changes in morphology of conceptus trophectoderm and 2) induce adhesion between luminal epithelium and trophectoderm essential for implantation and placentation [1].
  • The potential involvement of OPN in the implantation adhesion cascade in sheep was investigated by examining temporal, spatial, and potential functional relationships between OPN, Muc-1, and integrin subunits during the estrous cycle and early pregnancy [5].
  • Osteopontin (OPN) is a component of the extracellular matrix that interacts with cell surface receptors, including integrins, to mediate cell adhesion, migration, differentiation, survival, and immune function [6].
  • Collectively, the present results support the hypothesis that ovine OPN is a component of histotroph secreted by the uterine GE that accumulates at the uterine-placental interface to influence maternal-fetal interactions throughout gestation in sheep [7].
  • Intrauterine infusion of roIFNtau did not affect OPN gene expression or secretion in any of the steroid treatments [8].

Anatomical context of OPN

  • Therefore, the present study determined temporal and spatial alterations in OPN mRNA and protein expression in the ovine uterus between Days 25 and 120 of pregnancy [7].
  • In pregnant ewes, OPN mRNA was also expressed by the glandular epithelium [9].
  • The OPN mRNA in total ovine endometrium increased 30-fold between Days 40 and 80 of gestation [7].
  • Osteopontin (OPN) is an acidic phosphorylated glycoprotein component of the extracellular matrix that binds to integrins at the cell surface to promote cell-cell attachment and cell spreading [8].
  • Osteopontin (OPN) is a phosphorylated and glycosylated, secreted protein that is present in various epithelial cells and biological fluids [7].

Associations of OPN with chemical compounds

  • Therefore, progesterone and/or interferon-tau (IFNtau) may regulate OPN expression in the uterine GE [8].
  • These results provide a physiological framework for the role of OPN, a potential mediator of implantation in sheep, as a bridge between integrin heterodimers expressed by Tr and uterine LE responsible for adhesion for initial conceptus attachment [5].
  • Immunoreactive OPN was localized to luminal and glandular epithelia of both cyclic and pregnant ewes, and to trophectoderm of Day 19 conceptuses [1].
  • OPN is an acidic glycoprotein that fragments upon freezing and thawing or treatment with proteases including thrombin [9].
  • Functional analysis of potential OPN interactions with conceptus and endometrial integrins was performed on LE and Tr cells in vitro using beads coated with OPN, poly-L-lysine, or recombinant OPN in which the Arg-Gly-Asp sequence was replaced with RGE or RAD [5].

Other interactions of OPN

  • In sheep and humans, OPN is proposed to be a secretory product of uterine glandular epithelium (GE) that binds to uterine luminal epithelium (LE) and conceptus trophectoderm to mediate conceptus attachment, which is essential to maintain pregnancy through the peri-implantation period [7].
  • Until now the expression patterns of integrin alpha V beta 3 and osteopontin in the pregnant bovine uterus were unknown [10].

Analytical, diagnostic and therapeutic context of OPN

  • Three forms of immunoreactive OPN proteins (70, 45, and 24 kDa) were detected by 1D PAGE and Western blot analysis of endometrial extracts [1].
  • In both cyclic and pregnant ewes, in situ hybridization analysis showed that OPN mRNA was localized on unidentified immune cells within the stratum compactum of the endometrium [9].
  • In situ hybridization and immunofluorescence analyses revealed that the predominant source of OPN mRNA and protein throughout pregnancy was the uterine GE [7].
  • In Western ligand blotting (immunoblotting) experiments, the 72-kDa protein bound not only BSP but also radiolabeled fibronectin, fibrinogen, vitronectin, thrombospondin, and, to some extent, collagen [2].
  • Immunocytochemistry and conventional stains were used to detect lineage-typical markers: fat vacuoles and peroxisome proliferation-acitivated receptor gamma2 (PPAR) served to detect adipoblasts, whereas osteopontin (OP) was used to characterize osteoblasts [11].


  1. Ovine osteopontin: II. Osteopontin and alpha(v)beta(3) integrin expression in the uterus and conceptus during the periimplantation period. Johnson, G.A., Burghardt, R.C., Spencer, T.E., Newton, G.R., Ott, T.L., Bazer, F.W. Biol. Reprod. (1999) [Pubmed]
  2. Identification of a Staphylococcus aureus extracellular matrix-binding protein with broad specificity. McGavin, M.H., Krajewska-Pietrasik, D., Rydén, C., Höök, M. Infect. Immun. (1993) [Pubmed]
  3. The ovine Booroola fecundity gene (FecB) is linked to markers from a region of human chromosome 4q. Montgomery, G.W., Crawford, A.M., Penty, J.M., Dodds, K.G., Ede, A.J., Henry, H.M., Pierson, C.A., Lord, E.A., Galloway, S.M., Schmack, A.E. Nat. Genet. (1993) [Pubmed]
  4. In situ hybridization to show sequential expression of osteoblast gene markers during bone formation in vivo. Zhou, H., Choong, P., McCarthy, R., Chou, S.T., Martin, T.J., Ng, K.W. J. Bone Miner. Res. (1994) [Pubmed]
  5. Muc-1, integrin, and osteopontin expression during the implantation cascade in sheep. Johnson, G.A., Bazer, F.W., Jaeger, L.A., Ka, H., Garlow, J.E., Pfarrer, C., Spencer, T.E., Burghardt, R.C. Biol. Reprod. (2001) [Pubmed]
  6. Osteopontin expression in uterine stroma indicates a decidualization-like differentiation during ovine pregnancy. Johnson, G.A., Burghardt, R.C., Joyce, M.M., Spencer, T.E., Bazer, F.W., Pfarrer, C., Gray, C.A. Biol. Reprod. (2003) [Pubmed]
  7. Osteopontin is synthesized by uterine glands and a 45-kDa cleavage fragment is localized at the uterine-placental interface throughout ovine pregnancy. Johnson, G.A., Burghardt, R.C., Joyce, M.M., Spencer, T.E., Bazer, F.W., Gray, C.A., Pfarrer, C. Biol. Reprod. (2003) [Pubmed]
  8. Progesterone modulation of osteopontin gene expression in the ovine uterus. Johnson, G.A., Spencer, T.E., Burghardt, R.C., Taylor, K.M., Gray, C.A., Bazer, F.W. Biol. Reprod. (2000) [Pubmed]
  9. Ovine osteopontin: I. Cloning and expression of messenger ribonucleic acid in the uterus during the periimplantation period. Johnson, G.A., Spencer, T.E., Burghardt, R.C., Bazer, F.W. Biol. Reprod. (1999) [Pubmed]
  10. Immunohistochemical localization of integrin alpha V beta 3 and osteopontin suggests that they do not interact during embryo implantation in ruminants. Kimmins, S., Lim, H.C., MacLaren, L.A. Reprod. Biol. Endocrinol. (2004) [Pubmed]
  11. Ovine cord blood accommodates multipotent mesenchymal progenitor cells. Jäger, M., Bachmann, R., Scharfstädt, A., Krauspe, R. In Vivo (2006) [Pubmed]
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