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M M Roberson

Publications and source records attributed to M M Roberson.

11 recordsLinked to original sources
PubMed1988

Endogenous lectin secretion into the extracellular matrix of early embryos of Xenopus laevis.

An endogenous galactoside-binding lectin with subunit molecular weight of 43,000-45,000, previously detected in unfertilized eggs of Xenopus laevis, persists at high levels in embryos through gastrulation. During embryonic development the lectin is found in cytoplasmic vesicles, and then is secreted into extracellular matrix which is prominent around the blastopore and on the roof of the blastocoel. The lectin is also found in the extracellular material in the developing neural fold. The presence of lectin at sites of active morphogenetic movements raises the possibility that it participates in the formation of an extracellular matrix that influences these processes.

Animals↗
PubMed1986

Secretion of a cytoplasmic lectin from Xenopus laevis skin.

The skin of Xenopus laevis contains a soluble beta-galactoside-binding lectin with a approximately 16,000-mol-wt subunit. It resembles similar lectins purified from a variety of tissues from other vertebrates, and differs from two other soluble X. laevis lectins from oocytes and serum that bind alpha-galactosides. The skin lectin is concentrated in the cytoplasm of granular gland and mucous gland cells, as demonstrated by immunohistochemistry with the electron microscope. Upon injection with epinephrine, there is massive secretion of the cytoplasmic lectin from the granular gland cells.

Amino Acids↗
PubMed1985

Galactoside-binding serum lectin of Xenopus laevis. Estrogen-dependent hepatocyte synthesis and relationship to oocyte lectin.

Xenopus laevis serum contains a lectin which binds alpha- and beta-galactosides. It was purified to homogeneity by affinity chromatography and consists of a single subunit with Mr approximately 69,000, associated in a multimer. The lectin is synthesized and secreted by hepatic parenchymal cells, and its synthesis is increased about 2-fold by estrogen treatment, both in vivo and in primary cell cultures. The serum lectin has the same carbohydrate binding properties as an oocyte lectin from X. laevis described previously, is immunologically cross-reactive, and shows similarities in its peptide map. However, marked differences in amino acid composition preclude the possibility that the serum lectin is a precursor of the oocyte lectin.

Amino Acids↗
PubMed1984

Localization of soluble endogenous lectins and their ligands at specific extracellular sites.

Soluble lectins of chicken, rat, frog, and the cellular slime mold, Dictyostelium discoideum, were purified and specific antibodies raised against these proteins were used to immunohistochemically localize the lectins in and around the tissues in which they were synthesized. Within cells, some of these soluble lectins (chicken-lactose-lectin-II in intestinal goblet cells, discoidin II in prespore cells) appear to be concentrated within vesicles whereas others (e.g., rat beta-galactoside lectin in pulmonary alveolar and smooth muscle cells) appear to be free in the cytoplasm. All of these lectins are eventually secreted to extracellular sites in developing or adult tissues. The sites include mucin (chicken-lactose-lectin-II in intestine); developing extracellular matrix (chicken-lactose-lectin-I in muscle; Xenopus laevis lectin in blastula stage embryos); slime (discoidin I); developing spore coat (discoidin II); and a specialized extracellular matrix, elastic fibers (rat beta-galactoside lectin in lung). In cases where this has been studied in detail (discoidin I, discoidin II, and chicken-lactose-lectin-II), the lectin is associated with a complementary extracellular ligand, at least transiently. Lectin-ligand interactions presumably confer specialized properties in these particular extracellular domains.

Animals↗
PubMed1983

Xenopus laevis lectin is localized at several sites in Xenopus oocytes, eggs, and embryos.

The endogenous lectin of Xenopus laevis oocytes, unfertilized eggs, and blastula-stage embryos was immunohistochemically localized using a highly specific antiserum. Each tissue was examined with several techniques, including paraformaldehyde or glutaraldehyde fixation, frozen or plastic sections, and immunofluorescence or immunoperoxidase staining. In oocytes and unfertilized eggs, lectin was detected in association with yolk platelets, cortical granules, and the vitelline envelope. In embryos, cortical granules had disappeared and lectin was found in the cleavage furrows between the embryonic cells. The distribution of the lectin suggests that it plays more than one role in this developing system.

Animals↗
PubMed1982

Lectin from embryos and oocytes of Xenopus laevis. Purification and properties.

Soluble extracts of Xenopus laevis blastula stage embryos, oocytes, and adult liver contain lectin activities detected by agglutination of trypsinized, glutaraldehyde-fixed rabbit erythrocytes. Lectin from the embryos and oocytes was purified by affinity chromatography on a column derivatized with melibiose. Trace contaminants were removed either by preparative isoelectric focusing or by gel filtration. Based on its behavior on Sepharose 6B the purified oocyte lectin has an apparent molecular weight of approximately 480,000. On sodium dodecyl sulfate polyacrylamide gel electrophoresis under reducing conditions there were two major bands with molecular weight ranges of about 43,000 and 45,000, with diffuse trails. Since the purified lectin contains about 20% saccharides by weight and since both bands are glycosylated, diffuseness might be due to variable glycosylation. Heterogeneity was indicated by isoelectric focusing in polyacrylamide gels, which showed four protein bands with isoelectric points ranging from 4.4 to 4.9. Lectins from both embryos and oocytes comprised about 1 to 2% of the total soluble protein and could not be distinguished by sodium dodecyl sulfate polyacrylamide gel electrophoresis. However, the specific hemagglutination activity of the purified oocyte lectin was, on the average, 7-fold higher. Levels in crude extracts of liver were 3 orders of magnitude lower than those from oocytes. The hemagglutination activities of the lectins from embryos, oocytes, and adult liver required Ca2+ and were blocked by similar concentrations of both alpha- and beta-galactosides.

Amino Acids↗
PubMed1981

Heparin-inhibitable lectins: marked similarities in chicken and rat.

Extracts of young rat lung contain a heparin-inhibitable lectin that closely resembles one recently purified from chicken liver. Both lectins interact with heparin and N-acetyl-D-galactosamine, and were purified by gel filtration on Sepharose CL-2B followed by affinity chromatography on heparin-Sepharose. They both behave as high molecular weight aggregates that can be dissociated into two peptides with apparent molecular weights of 13,000 and 16,000 by gel electrophoresis in SDS. Samples of purified lectin contained up to 20% DNA by weight, and the degree of lectin aggregation and hemagglutination activity was greatly reduced by treatment with micrococcal nuclease without inhibiting heparin-binding activity. Association of lectin with DNA is an artifact of homogenization in high salt, since only 2% of the lectin is found associated with a purified nuclear fraction.

Animals↗
PubMed1980

Carbohydrate-binding component of amphibian embryo cell surfaces: restriction to surface regions capable of cell adhesion.

Superficial cells from early amphibian embryos display regional specializations of their cell surfaces. That portion of the plasma membrane facing the perivitelline space (apical surface) is nonadhesive, whereas, in the same cell, the lateral and basal portions of the plasma membrane will adhere to other cells. These adhesive differences are maintained on single cells that have been dissociated from the intact embryo. Extracts of cleavage-stage Rana pipiens embryos are capable of agglutinating formalinized sheep erythrocytes. The hemagglutination activity can be blocked by a yeast mannan and a family of glycoproteins containing high levels of mannose, indicating the presence of a lectin with oligomannosyl specificity. The cell surface location of this carbohydrate-binding component can be demonstrated by the ability of the formalinized sheep erythrocytes to form rosettes with living dissociated embryonic superficial cells. Rosette formation is blocked by the same inhibitors that are effective in blocking the activity of the crude extracts. The formalinized sheep erythrocytes form rosettes only to those cell surface regions of the superficial cells that are capable of adhering to other amphibian embryo cells. Receptors for concanavalin A, a lectin that binds D-mannose and D-glucose residues, have also been shown to be present exclusively over the adhesive regions of the superficial cells. The involvement of a carbohydrate-binding component with oligomannosyl specificity in the adhesive mechanisms of these cells is suggested by this restriction of both the embryonic amphibian lectin and its possible receptors (concanavalin A receptors) to adhesive regions of the cell surface.

Animals↗