Hereditary retinoblastoma: can balanced insertion entirely explain the differences of expressivity among families?

Summary Although the retinoblastoma gene has been isolated and sequenced, the difference in penetrance and expressivity among families has not yet been fully explained. Balanced chromosomal insertion involving the 13q14 regions has been shown to account for some families with several unaffected carriers. Since there could be cases with karyotypically undetectable insertions, we tested whether this mechanism was general enough to explain the whole difference in expressivity among families. Using 166 pedigrees, reported in nine series available in the literature (including our own), we conclude that balanced insertion cannot entirely explain the familial data, even if we allow for a reduced viability of unbalanced gametes. Other mechanisms are proposed and discussed in this paper.     

Identification of interferon-gamma as the lymphokine that mediates leukotriene B4-induced immunoregulation

Leukotriene B4 (LTB4) has been shown to modulate lymphocyte responses in both a positive and a negative way, depending on the particular cell subsets it interacts with. Recent evidence also indicates that LTB4 can directly affect the production of cytokines such as interleukin 1 (IL 1) or interleukin 2 (IL 2) and interferon-gamma (IFN-gamma). In this report, we present evidence that human T cells pulsed with LTB4 modulate IL 1 production by human monocytes by secreting IFN-gamma. In fact, we found that LTB4-pulsed T cells were capable of inducing a suppression of lymphocyte proliferation if allowed to interact with monocytes, but that this suppression was reversed to an enhancing effect when monocytes were treated with the cyclooxygenase inhibitor indomethacin. Furthermore, LTB4-pulsed T cells released a soluble factor that would mediate both effects. This factor was found to be IFN-gamma, because affinity-purified IFN-gamma could reproduce the effects, and a rabbit polyclonal anti-serum to human IFN-gamma could block the activities of supernatants from LTB4-pulsed T cells. LTB4 was also shown to enhance IFN-gamma production by T4+ T cells and to inhibit IFN-gamma production by T8+ T cells. These results suggest that LTB4 may regulate immune cell functions by inducing IFN-gamma production by T4+ cells.     

Differential regulation by dexamethasone of glucocorticoid receptor messenger RNA concentrations in neuronal cultures derived from fetal rat hypothalamus and cerebral cortex

1. Differential regulation, by dexamethasone, of glucocorticoid receptor gene expression was studied in three different neuronal cultures derived from hypothalamus amygdala, and cerebral cortex. 2. Cellular glucocorticoid receptor (GR) mRNA concentration was measured by hybridization using a 32P-labeled RNA probe complementary to a 2.2-kb fragment of the glucocorticoid receptor mRNA. Changes in the amount of GR mRNA were evaluated in relation to the content of beta-actin mRNA. 3. In cells derived from either hypothalamus or cerebral cortex, we observed a complex pattern of GR mRNA concentrations which were characterized by cyclic variations of GR mRNA content during continuous treatment with dexamethasone for up to 72 hr. 4. In contrast to cells derived from the hypothalamus where a persistent 30-40% reduction in GR mRNA levels was seen for up to a least 72 hr, we observed, in cells derived from the cerebral cortex, a sustained increased (1.4-fold) of the GR mRNA at this same time interval.     

Enhancer and promoter elements directing activation and glucocorticoid repression of the alpha 1-fetoprotein gene in hepatocytes.

Mutations were introduced in 7 kilobases of 5'-flanking rat alpha 1-fetoprotein (AFP) genomic DNA, linked to the chloramphenicol acetyltransferase gene. AFP promoter activity and its repression by a glucocorticoid hormone were assessed by stable and transient expression assays. Stable transfection assays were more sensitive and accurate than transient expression assays in a Morris 7777 rat hepatoma recipient (Hepa7.6), selected for its strong AFP repression by dexamethasone. The segment of DNA encompassing a hepatocyte-constitutive chromatin DNase I-hypersensitive site at -3.7 kilobases and a liver developmental stage-specific site at -2.5 kilobases contains interacting enhancer elements sufficient for high AFP promoter activity in Hepa7.6 or HepG2 cells. Deletions and point mutations define an upstream promoter domain of AFP gene activation, operating with at least three distinct promoter-activating elements, PEI at -65 base pairs, PEII at -120 base pairs, and DE at -160 base pairs. PEI and PEII share homologies with albumin promoter sequences, PEII is a near-consensus nuclear factor I recognition sequence, and DE overlaps a glucocorticoid receptor recognition sequence. An element conferring glucocorticoid repression of AFP gene activity is located in the upstream AFP promoter domain. Receptor-binding assays indicate that this element is the glucocorticoid receptor recognition sequence which overlaps with promoter-activating element DE.     

Alport syndrome: a genetic study of 31 families

Thirty one families with Alport syndrome including 3 families with associated syndromes were studied. The location of the COL4A5 gene, responsible for the Alport syndrome, was determined by linkage analysis with eight probes of the Xq arm and by a radiation hybrid panel. Concordant data indicated the localization of the Alport gene between DXS17 and DXS11. Four deletions and one single base mutation of the COL4A5 gene were detected. Homogeneity tests failed to show any evidence of genetic heterogeneity superimposed on clinical heterogeneity for ophthalmic signs and end-stage renal disease age.     

Assignment by in situ hybridization of a fibroblast growth factor receptor gene to human chromosome band 10q26

Summary A 2.3-kb cDNA probe for the human bek fibroblast growth factor receptor was used to determine the chromosomal localization of the corresponding gene by in situ hybridization. The results show that this gene, a form of which is amplified in some poorly differentiated stomach cancers, is localized on chromosome region 10q26. The two previously identified fibroblast growth factor receptor genes are thus not on the same chromosome, as the related fig (fms-like gene) fibrovblast growth factor receptor gene has previously been mapped to human chromosome region 8p12.     

Structure of the B880 holochrome of Rhodospirillum rubrum as studied by the radiation inactivation method

Chromatophores from photoreaction centerless strain F24 of Rhodospirillum rubrum were subjected to different doses of gamma radiation. Target theory was applied to the induced decay of the B880 holochrome pigments as analyzed by absorption spectroscopy of the membranes and of organic solvent extracts. Destruction of bacteriochlorophyll is associated with a target size of 7 kDa. This indicates that each one of the two different 6-kDa holochrome polypeptides binds one molecule of this pigment. The target size of spirilloxanthin, 12 kDa, suggests that both polypeptides contribute to the binding site of this carotenoid. The 880 nm absorption band and the oxidation-induced 1225 nm band have a target size of 14 kDA. Therefore, these bands are due to interaction between two bacteriochlorophyll molecules, each one of which resides on a different polypeptide. This 14-kDa complex decays into a bacteriochlorophyll monomer associated with a target size of 7 kDa. The absolute absorption spectra of the protein-bound bacteriochlorophyll pair and monomer are presented.     

Isolation and partial characterization of the messenger RNA encoding the B880 holochrome protein of Rhodospirillum rubrum

The B880 holochrome messenger RNA was extracted from cultures of the photosynthetic bacterium Rhodospirillum rubrum. It was purified by chromatography on Sepharose 4B followed by sucrose density gradient centrifugation. The purified fractions were shown to program an Escherichia coli cell-free system into synthesizing both the alpha and the beta polypeptides of the holochrome. The translation products were identified by immunoprecipitation with specific antibodies raised against these polypeptides. The latter are effective competitors with the translation products for antigen-antibody complex formation. The purest mRNA preparations contained approximately 33% holochrome messenger RNA activity. Its most probable size, as determined by agarose gel electrophoresis in the presence of 6 M urea or methylmercuric hydroxide, is approximately 620 nucleotides. Since the combined sizes of the alpha and beta polypeptides add up to only 106 amino acid residues, we conclude that the holochrome mRNA is most probably polycistronic.