Expression of the fragile (X) chromosome in an interspecific somatic cell hybrid

Interspecific somatic cell hybrids were constructed between a Chinese hamster lung cell line deficient in hypoxanthine phosphoribosyltransferase and two lymphoblastoid cultures (GM 4025 and GM 3200) from unrelated males affected with the fragile (X) syndrome. Thirteen independent colonies survived selection in hypoxanthine-azaserine, while only one colony survived selection in hypoxanthine-aminopterin-thymidine. One hybrid formed from GM 4025 was found to contain a human X chromosome as the only detectable human chromosome in the majority of cells analyzed. Induction of fragile (X) expression in this hybrid at frequencies up to 20% was achieved by treatments with 5-fluoro-2'-deoxyuridine (5 X 10(-8) M or 1 X 10(-7) M) or methotrexate (5 X 10(-6) or 1 X 10(-5) for 12 h. Use of the somatic cell hybrid system may allow study of the fragile (X) from different patients on a homogeneous xenogeneic background and may provide a better system for characterization of the fragile (X) at the biochemical and molecular level.     

Surface labelling of oligodendrocytes with anti-myelin serum in cell cultures from the rat brain

Summary Antiserum produced in rabbits against purified myelin contains antibodies that bind to the surface of cells having multiple branched processes in live cultures of cerebral hemispheres of newborn rats. The identity of these cells was determined by double immunolabelling experiments with other specific antigenic markers (W1 Wolfgram protein, myelin basic proteins, glial fibrillary acidic protein). It was demonstrated that the cells are a subclass of oligodendrocytes which have reached a certain degree of maturation; nearly all of them contain basic proteins. Indeed, a number of oligodendrocytes, that contain the W 1 protein, and may or may not have processes, are not surface-labelled in similar conditions. The usefulness of such an anti-myelin serum in the isolation of pure oligodendrocytes is discussed.J.L.N. is Chargé de Recherche au CNRSDirector: Professor Guy Vincendon     

Ocrl1, a PtdIns(4,5)P(2) 5-phosphatase, is localized to the trans-Golgi network of fibroblasts and epithelial cells.

PtdIns(4,5)P(2) and PtdIns(4,5)P(2) 5-phosphatases play important roles in diverse aspects of cell metabolism, including protein trafficking. However, the relative importance of the PtdIns(4,5)P(2) 5-phosphatases in regulating PtdIns(4,5)P(2) levels for specific cell processes is not well understood. Ocrl1 is a PtdIns(4,5)P(2) 5-phosphatase that is deficient in the oculocerebrorenal syndrome of Lowe, a disorder characterized by defects in kidney and lens epithelial cells and mental retardation. Ocrl1 was originally localized to the Golgi in fibroblasts, but a subsequent report suggested a lysosomal localization in a kidney epithelial cell line. In this study we defined the localization of ocrl1 in fibroblasts and in two kidney epithelial cell lines by three methods: immunofluorescence, subcellular fractionation, and a dynamic perturbation assay with brefeldin A. We found that ocrl1 was a Golgi-localized protein in all three cell types and further identified it as a protein of the trans-Golgi network (TGN). The TGN is a major sorting site and has the specialized function in epithelial cells of directing proteins to the apical or basolateral domains. The epithelial cell phenotype in Lowe syndrome and the localization of ocrl1 to the TGN imply that this PtdIns(4,5)P(2) 5-phosphatase plays a role in trafficking. (J Histochem Cytochem 48:179-189, 2000)     

Parathyroid hormone-related peptide mediates hypercalcemia in an islet cell tumor of the pancreas.

Hypercalcemia occurring in a patient with an islet cell carcinoma of the pancreas suggests the diagnosis of Multiple Endocrine Neoplasia Type I and associated hyperparathyroidism. We describe a patient with an islet cell carcinoma and hypercalcemia in whom low concentrations of PTH, the absence of skeletal metastases, hypophosphatemia, and elevated nephrogenous cAMP alternatively suggested the syndrome of humoral hypercalcemia of malignancy. The peptide PTHrP was measured in the patient's serum during the course of therapy by an immunoradiometric assay directed toward the midportion of the molecule. Hypercalcemia was treated with an investigational aminobisphosphonate. The concentration of PTHrP[56-86] increased over time and fell after the patient received chemotherapy directed toward the islet cell tumor.     

Cell free synthesis of rat brain myelin proteolipids and their identification by immunoprecipitation

Rat-brain poly(A)-containing RNAs were prepared by affinity chromatography on Poly(U)-Sepharose and translated in the rabbit reticulocyte lysate system in the presence of [³⁵S]-methionine. By using antimyelin proteolipids antibodies, immunoreactive polypeptides of 23.5 K and 19 K were isolated from the translation products : they had electrophoretic mobilities similar to those of the rat brain myelin proteolipids apoproteins.