Although ES cells may provide treatment for degenerative disease in the future, their unlimited self-renewal and high differentiation potential poses the risk of tumor induction after engraftment. Thus, more care must be taken before using ES cell transplantation as a therapeutic option for patients with degenerative disease.

Our data indicate that bone marrow-derived stromal cells of horses can be characterized as MSCs. Equine MSCs have a high transduction rate and migratory potential and adapt to scaffold material in culture. As an autologous cell population, equine MSCs can be regarded as a promising cell population for tissue engineering in lesions of the musculoskeletal system in horses.

No abstract

To address the functions of Rac1 in keratinocytes of the basal epidermal layer and in the outer root sheath of hair follicles, we generated transgenic mice expressing a dominant inhibitory mutant of Rac, N17Rac1, under the control of the keratin 14 promoter. These mice do not exhibit an overt skin phenotype but show protracted skin wound re-epithelialization. Investigation into the underlying mechanisms revealed that in vivo both proliferation of wound-edge keratinocytes and centripetal migration of the neo-epidermis were impaired. Similar results were obtained in mice with an epidermis-specific deletion of Rac1. Primary epidermal keratinocytes that expressed the N17Rac1 transgene were less proliferative than control cells and showed reduced ERK1/2 phosphorylation upon growth factor stimulation. Adhesion, spreading, random migration and closure of scratch wounds in vitro were significantly inhibited on collagen I and, to a lesser extent, on fibronectin. Stroboscopic analysis of cell dynamics (SACED) of N17Rac1 transgenic and control keratinocytes identified decreased lamella-protrusion persistence in connection with increased ruffle frequency as a probable mechanism for the observed impairment of keratinocyte adhesion and migration. We conclude that Rac1 is functionally required for normal epidermal wound healing and, in this context, exerts a dual function – namely the regulation of keratinocyte proliferation and migration.

Direct observation of the progress of a catalysed reaction in crystals of glycogen phosphorylase b has been made possible through fast crystallographic data collection achieved at the Synchrotron Radiation source at Daresbury, UK. In the best experiments, data to 2.7 A resolution (some 108 300 measurements; 21 200 unique reflections) were measured in 25 min. In a series of time-resolved studies in which the control properties of the enzyme were exploited in order to slow down the reaction, the conversion of heptenitol to heptulose-2-phosphate, the phosphorylysis of maltoheptaose to yield glucose-l-phosphate and the oligosaccharide synthesis reaction involving maltotriose and glucose-l-phosphate have been monitored in the crystal. Changes in electron density in the difference Fourier maps are observed as the reaction proceeds not only at the catalytic site but also the allosteric and glycogen storage sites. Phosphorylase b is present in the crystals in the T state and under these conditions exhibits low affinity for both phosphate =nd oligosaccharide substrates. There are pronounced conformational changes associated with the formation and binding of the high-affinity dead-end product, heptulose-2-phosphate, which show that movement of an arginie residue, Arg 569, is critical for formation of the substrate-phosphate recognition site. The results are discussed with reference to proposals for the enzymic mechanism of phosphorylase. The feasibility for time-resolved studies on other systems and recent advances in this area utilizing Laue diffraction are also discussed.

The structural relationships between substrate and pyridoxal phosphate in glycogen phosphorylase b (EC 2.4.1.1) have been studied by X-ray diffraction experiments at 3-A resolution. Recent work [Klein, H. W., Im, M. J., & Helmreich, E. J. M. (1984) in Chemical and Biological Aspects of Vitamin B6 Catalysis (Evangelopoulos, A. E., Ed.) pp 147-160, Liss, New York] has shown that phosphorylase in the presence of inorganic phosphate catalyzes the conversion of heptenitol to heptulose 2-phosphate. The latter compound is a dead-end product and a most potent inhibitor (Ki = 14 microM). The X-ray diffraction studies show that heptenitol binds at the catalytic site of phosphorylase in a position essentially identical with that observed for the glucopyranose moiety of glucose 1-phosphate. Incubation of a phosphorylase b crystal for 50 h in a solution containing the substrates heptenitol and inorganic phosphate and the activators AMP and maltohetaose resulted in the formation of a phosphorylated product bound at the active site. The structure of this product, as analyzed by a difference Fourier synthesis at 3 A, is consistent with that of heptulose 2-phosphate. Analysis of the surrounding soak solution by thin-layer chromatography showed that heptulose 2-phosphate was produced under these conditions. Heptulose 2-phosphate binds with its glucopyranose moiety in the same position as that for glucose 1-phosphate, but there is a marked difference in phosphate positions. The presence of the methyl group in the beta-configuration in heptulose 2-phosphate forces a change in the torsion angle O5-C1-O1-P from 117 degrees as observe in glucose 1-phosphate to -136 degrees in heptulose 2-phosphate. The "down" position of the phosphate (with respect to the crystallographic z axis) results in a change in the distance between the 5'-phosphorus atom of the pyridoxal phosphate and the phosphorus atom of the substrate from 6.8 (with glucose 1-phosphate) to 4.5 A (with heptulose 2-phosphate). The closest distance between the phosphate oxygen of the cofactor and a phosphate oxygen of heptulose 2-phosphate is 2.7 A, and it is assumed that there must be a hydrogen bond between them. These observations are consistent with the NMR experiments reported in the preceding paper in which sharing of a proton between heptulose 2-phosphate and pyridoxal 5'-phosphate is observed [Klein, H.W., Im, M. J., Palm, D., & Helmreich, E. J. M. (1984) Biochemistry (preceding paper in this issue)].(ABSTRACT TRUNCATED AT 400 WORDS)

Our data indicate that mesenchymal stem cells can prolong photoreceptor survival in the rhodopsin knockout mouse, also providing evidence of a therapeutical benefit in retinitis pigmentosa.

Grb2-associated binder-1 (Gab-1) has been identified recently in a cDNA library of glioblastoma tumors and appears to play a central role in cellular growth response, transformation, and apoptosis. Structural and functional features indicate that Gab-1 is a multisubstrate docking protein downstream in the signaling pathways of different receptor tyrosine kinases, including the epidermal growth factor receptor (EGFR). Therefore, the aim of the study was to characterize the phosphorylation of recombinant human Gab-1 (hGab-1) protein by EGFR in vitro. Using the pGEX system to express the entire protein and different domains of hGab-1 as glutathione S-transferase proteins, kinetic data for phosphorylation of these proteins by wheat germ agglutinine-purified EGFR and the recombinant EGFR (rEGFR) receptor kinase domain were determined. Our data revealed similar affinities of hGab-1-C for both receptor preparations (KM = 2.7 microM for rEGFR vs 3.2 microM for WGA EGFR) as well as for the different recombinant hGab-1 domains. To identify the specific EGFR phosphorylation sites, hGab-1-C was sequenced by Edman degradation and mass spectrometry. The entire protein was phosphorylated by rEGFR at eight tyrosine residues (Y285, Y373, Y406, Y447, Y472, Y619, Y657, and Y689). Fifty percent of the identified radioactivity was incorporated in tyrosine Y657 as the predominant peak in HPLC analysis, a site exhibiting features of a potential Syp (PTP1D) binding site. Accordingly, GST-pull down assays with A431 and HepG2 cell lysates showed that phosphorylated intact hGab-1 was able to bind Syp. This binding appears to be specific, because it was abolished by changing the Y657 of hGab-1 to F657. These results demonstrate that hGab-1 is a high-affinity substrate for the EGFR and the major tyrosine phosphorylation site Y657 in the C terminus is a specific binding site for the tyrosine phosphatase Syp.