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G G Gundersen

Publications and source records attributed to G G Gundersen.

43 records · Page 3Linked to original sources
PubMed1986

Microtubule arrays in differentiated cells contain elevated levels of a post-translationally modified form of tubulin.

Tyrosinated (Tyr) and detyrosinated (Glu) alpha-tubulins are post-translationally modified species that differ by a single amino acid at their respective C-termini. We have examined the distribution of these two species by immunofluorescence in proliferating and differentiated cells using antisera specifically reactive with each of the forms. In proliferating PtK1 cells, Tyr tubulin was the predominant form in almost every cytoplasmic microtubule (MT); only a few MTs contained detectable Glu tubulin. In contrast, staining of centrioles and primary cilia of PtK1 cells suggested that Glu tubulin was the predominant form in these stable assemblies of MTs. An examination of the distribution (by immunofluorescence) and relative amount (by immunoblot analysis) of the two forms of tubulin in the stable assemblies of MTs present in cultured neuronal cells (neurites), sperm and tracheal cells (axonemes and basal bodies), and platelets and erythrocytes (marginal bands) revealed that, in general, the MTs in these arrays contained substantially elevated levels of Glu tubulin in comparison with the levels in MTs of cultured cells. The one exception, the marginal band of toad erythrocytes, which contained only Tyr tubulin, demonstrates that an elevated level of Glu tubulin is not an obligate feature of a stable array of MTs. Nonetheless, an elevated level of Glu tubulin may be a useful indicator of stable MTs in differentiated cells. It is important to note that commonly used sources of tubulin (e.g., brain or flagella) necessarily yield tubulin that differs strikingly from tubulin of proliferating cells in its content of Glu tubulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Hapten-mediated immunopurification of membrane proteins labeled with fluorescein derivatives.

The behavior of cell surface components labeled with fluorochromes can be studied by fluorescence microscopy and spectroscopy; further structural analyses would be facilitated by purification of the labeled components. We have developed a protocol for identifying the targets for labeling with fluorescein derivatives, by using 125I- diiodofluorescein isothiocyanate ( 125IFC ) and for isolating the labeled components with anti-IFC immunoadsorbents. Anti-IFC antibodies obtained from rabbits immunized with IFC-hemocyanin were purified by affinity chromatography and coupled to CNBr-activated Sepharose 4B. The anti-IFC immunoadsorbents could then be used to isolate the entire set of 125IFC -proteins from crude detergent extracts of labeled sea urchin sperm, with a 70% yield and a purification of more than 250 fold. Nonspecific binding of unlabeled proteins to the immunoadsorbent was insignificant. When the immunoadsorbent IFC-protein complex was used directly as an immunogen, antibodies were obtained that reacted with the underivatized proteins that were targets for IFC labeling, as indicated by immunoblotting after gel electrophoresis. The antibodies also reacted with the surface of unlabeled sperm as shown by immunofluorescence. Thus, by treating the IFC-sperm proteins as a class, we obtained antibodies that recognized the unlabeled proteins in situ or in cell extracts. This approach should be generally useful in obtaining reagents directed against specific cell surface components.

Animals↗
PubMed1984

Distinct populations of microtubules: tyrosinated and nontyrosinated alpha tubulin are distributed differently in vivo.

A unique post-translational modification of tubulin has previously been described in which a tyrosine residue is reversibly added to the C terminus of the alpha-tubulin subunit. We have prepared peptide antibodies that specifically react (shown by competitive immunoassay and Western blots) with the tyrosinated (Tyr) and nontyrosinated (Glu) forms of alpha-tubulin. Immunofluorescence with these antibodies demonstrated that the distributions of Tyr and Glu tubulin in fixed cells were markedly different. Tyr tubulin was found throughout the interphase network of microtubules and in the metaphase spindle, whereas Glu tubulin was present in a limited subset of interphase microtubules and was absent from the astral fibers of the metaphase spindle. Double immunofluorescence showed that Glu and Tyr microtubules comprised distinct subsets of the total cellular microtubules. These results suggest that tyrosination is involved in the establishment of separate populations of microtubules that may functionally distinct.

Animals↗
PubMed1984

Sperm surface proteins persist after fertilization.

Certain sperm components labeled with fluorescein isothiocyanate or its radioactive derivative, 125I-diiodofluorescein isothiocyanate (125IFC), are transferred at fertilization to the egg, where they persist throughout early cleavage stages at a localized site in the embryo cytoplasm (Gabel, C. A., E. M. Eddy, and B. M. Shapiro, 1979, Cell, 18:207-215; Gundersen, G. G., C. A. Gabel, and B. M. Shapiro, 1982, Dev. Biol., 93:59-72). By using image intensification we have extended these observations in the sea urchin to the pluteus larval stage, in which greater than 60% of the embryos have localized fluorescent sperm components. Because of the unusual persistence of the sperm components in the embryo, a characterization of the nature of the labeled species in sea urchin sperm was undertaken. Approximately 10% of the 125IFC was in sperm polypeptides of Mr greater than 15,000. These proteins were on the sperm surface as shown by their sensitivity to externally added proteases. The remainder of the 125IFC in sperm was in several low-molecular-weight species, none of which was 125IFC-derivatized phospholipid. To determine if any labeled sperm polypeptides remained intact in the embryo after fertilization, 125IFC-labeled sperm proteins were recovered from one-cell and late gastrula stage embryos by using an anti-IFC immunoadsorbent. Most of the labeled sperm proteins were degraded shortly after fertilization; however, distinct sets of labeled polypeptides were recovered from both one-cell and gastrula stage embryos. Six of the labeled polypeptides recovered from both embryonic stages had identical SDS gel mobilities as labeled sperm polypeptides. Other polypeptides in the embryos appeared to arise from limited proteolysis of sperm proteins. Thus, in this physiological cell fusion system, individual sperm proteins are transferred to the egg at fertilization, and some persist intact or after specific, limited degradation long after gamete fusion, until at least the late gastrula stage.

Animals↗
PubMed1979

Lower bounds for eigenvalues of self-adjoint problems.

The equation y'' + [lambda - q(x)]y = 0 on (0, infinity) or (-infinity, infinity), in which q(x) --> infinity as x --> infinity or x --> +/- infinity, has a complete set of eigenfunctions with discrete eigenvalues {lambda(n)}(n=0) (infinity). We derive an inequality that contains lambda(n), by using a quick and elementary method that does not employ a comparison theorem or assume anything special. Explicit lower bounds for lambda(n) can often be easily obtained, and three examples are given. The method also gives respectable lower bounds for lambda(n) in the classical Sturm-Liouville case.

Journal Article↗