The developing kidney is a classic model system used to study mechanisms of organogenesis in mammals. Morphogenesis is regulated by epithelial-mesenchymal tissue interactions and involves inductive signaling across interactive tissue layers, ureter bud and metanephrogemc mesenchyme. As a response to induction a developmental program is activated in mesenchymal cells, and nephrons will develop as a result of mesenchymalepithelial transformation and subsequent simple morphogenesis which follows the process. Molecular genetic experimentation where gene function has been disrupted by gene targeting has proven to be fruitful in revealing the molecular mechanisms of kidney development and attracted attention again to this model system. These experiments indicated that sequentially activated genes regulate organogenesis and that cell signaling between epithelial ureter and kidney mesenchymal tissue is a key morphogenetic regulator. Molecular mediators from such gene families as transcription factors, cell adhesion molecules, kinases and secreted signaling molecules play an important role and are involved in the translation of cell behavior into morphogenesis. Recent data indicates that members of the Wnt gene family encoding secreted growth and differentiation factors act as classic tubule inducing signals. They are essential factors that control tubule induction and development in vitro and in vivo. A hypothetical model for some of the molecular mediators of tubule induction in vivo is presented.
The legume lectins are a family of carbohydrate binding proteins found in the Leguminosae plants and are used as a model system for studying protein-carbohydrate interactions. The different legume lectins show a remarkable range of sugar specificities, despite the high sequential and structural similarity of their subunits. Moreover, their subunits can associate into a number of different multimers. The unique variability of quaternary structure has implications for the formation of cross-linked lattices and binding of hydrophobic ligands.
The extracellular matrix serves as a scaffold for cell attachment (for review: Gumbiner, 1996), growth cone guidance during neurite outgrowth (for review: Luckenbill-Edds, 1997), cell migration (for review: Lauffenberger and Horwitz, 1996), cell polarity (for review: Drubin and Nelson, 1996) and cell death (for review: Adams and Watt, 1993) all underlying critical events in ontogenetic development and differentiation (for review: Adams and Watt, 1993). The molecular architecture of the extracellular matrix is created through specific interactions between laminins, collagen type IV, nidogen/entactin, and heparan- and chondroitin sulfate proteoglycans (Sanes, 1989; Timpl, 1989; Timpl and Brown, 1994; Yurchenco and O'Rear, 1994; Timpl and Brown, 1996; Timpl, 1996). Crucial molecules involved in the architecture of this defined supra-molecular assembly are members of the steadily growing laminin family (Burgeson et al., 1994; Engvall and Wewer, 1996). In this review we will focus on the unique molecular structure of laminins which enable self-interactions as well as interactions with different types of ligands, such as sulfated carbohydrates, other members of the extracellular matrix (nidogen/entactin, fibulins, perlecan, agrin and α-dystroglycan/cranin) and glycoproteins involved in cell adhesion (integrins and cell adhesion glycoproteins of the immunoglobulin superfamily). In particular, the involvement of carbohydrates in the interactions between laminin and its ligands will be discussed.
Polysialic acid (polySia), a polymer of sialic acid residue, is recognized as an oncodevelopmental antigen. In 1978, Salmonidae fish eggs were reported to have α2, 8-linked polysialylated glycoproteins (PSGPs) within the cortical alveoli. Subsequent studies showed the presence of another type of α2, 8-linked polysialylated glycoproteins, KDN-gps, in which deaminated neuraminic acid (KDN) is polymerized, in the vitelline envelope and ovarian fluid of salmonid fish. Even though it is expected that polySia chains of the PSGP and KDN-gp are somehow involved in cell adhesion and/or recognition events during fertilization and early embryogenesis, the precise function of these polySia chains remains largely unknown. To understand the biological significance of polySia structures during fertilization and embryonic development, research has been initiated to identify polySia-containing glycoproteins in sea urchin gametes. Sea urchins have been used for long time to study fertilization and early embryogenesis, because (i) it is relatively easy to collect their gametes and to observe their fertilization and their subsequent development and (ii) because the development of embryos can be synchronized. In fact, novel type of polySia structures in sea urchin egg jelly coat glycoprotein (polySia-gp) and the egg receptor glycoprotein for sperm were identified, respectively. Interestingly both polySia-gp and the egg receptor protein have a unique α2, 5-Oglycolyl-linked poly(Neu5Gc) chain in which each Neu5Gc residue is linked through the hydroxyl group of the glycolyl moiety of the penultimate Neu5Gc residue. The polySia chain in the egg receptor for sperm has an additional feature; a nonreducing terminal Neu5Gc is sulfated at the hydroxyl group of C9. Most interestingly, sulfated polySia chains found as a component of the receptor protein for sperm inhibited fertilization; the nonsulfated form of this polySia chains has little inhibitory activity. Recent finding regarding the structure and function of polySia chains in sea urchin eggs are mainly described in this review.
When an affinity ligand is linked to a soluble ionic matrix, the conjugate can specifically change the electrophoretic mobility of a protein which has affinity for the ligand. We refer to the conjugate as an “affinophore” and the electrophoresis using the affinophore “affinophoresis”. Succinylated glutathione is useful as a matrix for monoliganded affinophores. Iodoacetylated p-aminophenyl glycosides can be coupled to the thiol of the matrix to form affinophores for lectins. The affinophore having a mannoside as a ligand induced mobility change of pea lectin. The analysis of the competitive inhibition of the affinophoresis by neutral sugars using capillary electro-phoresis allowed the determination of the affinity constants for these sugars with very small amounts of a lectin sample and with high precision. The principle of the analysis, preparation of the affinophore and salient points of the experimental procedure ares described.
The links from the FCCA home page to useful information sites such as “Glyco Words” and “2D/3D-Sugar Map” are increasing. PubMed is also linked with the FCCA home page. As PubMed is a useful and free site for searching literature, many readers have taken advantage of this. Although journals on biochemistry, medicine, and pharmacy are available on the PubMed web page, journals on chemistry such as J. Am. Chem. Soc. and J. Org. Chem. are not available. Journals such as Carbohydrate Res. Glycoconjugate J., and Glycobiology etc. can be searched on the PubMed web page. In this manuscript, we intend to show how to access and search PubMed. In addition, the method of creating a database from the information obtained from PubMed will also be shown.