Astrocyte–neuron interactions in neurological disorders

Astrocytes have long been considered as just providing trophic support for neurons in the central nervous system, but recently several studies have highlighted their importance in many functions such as neurotransmission, metabolite and electrolyte homeostasis, cell signaling, inflammation, and synapse modulation. Astrocytes are, in fact, part of a bidirectional crosstalk with neurons. Moreover, increasing evidence is stressing the emerging role of astrocyte dysfunction in the pathophysiology of neurological disorders, including neurodegenerative disease, stroke, epilepsy, migraine, and neuroinflammatory diseases.     

Changes in cellular gene expression in rat thyroid epithelial cells transformed by the Kirsten murine sarcoma virus

We have exploited a recently characterized system of rat thyroid epithelial cells transformed by the wild-type (wt) and a temperature-sensitive (ts) mutant strain of the Kirsten murine sarcoma virus (Ki-MSV) in order to study the effects of the K-ras oncogene on the gene expression of differentiated thyroid epithelial cells. By using cDNAs isolated from normal thyroid glands as probes, we were able to identify three sets of cellular sequences whose expression is influenced by the v-K-ras oncogene. The first set of genes is irreversibly repressed by transformation with both the wt and the ts viruses. The second set of genes is repressed in the ts-Ki-MSV-transformed cells but not in the same cells grown at the nonpermissive temperature. A third set of genes is present at higher levels at the nonpermissive temperature than at the permissive temperature. This system has allowed us to isolate and characterize a number of cDNA clones belonging to each of these three sets of genes. These specific cDNAs are suitable probes to study phenotypical changes during transformation of epithelial cells.     

Gene deletion, a mechanism of induced mutation by arabinosyl nucleosides

9-β- -Arabinofuranosyl-2-fluoroadenine (F-ara-A) and 9-β- -arabinofuranosyladenine (ara-A) are purine nucleoside analogues which are incorporated into nucleic acids. This study demonstrates the mutagenic properties of F-ara-A and ara-A and provides evidence for mechanisms by which the arabinosyl nucleosides induce mutation. At the drug dosages that evoked exponential cell killing, F-ara-A and ara-A caused a significant increase in the number of 6-thioguanine-resistant mutants in Chinese hamster ovary cells. Southern analyses showed that 15 of 16 drug-induced mutants had lost all or part of the HPRT gene, whereas no loss of the gene was found in 4 spontaneous mutants. We conclude that both F-ara-A and ara-A induced mutation predominantly by causing deletion of genetic method. The remarkable frequency of gene deletion among these drug-induced mutations is discussed with respect to possible mechanisms of action of arabinosyl nucleosides in mutational studies.     

Human creatine kinase genes on chromosomes 15 and 19, and proximity of the gene for the muscle form to the genes for apolipoprotein C2 and excision repair.

The human chromosomal assignments of genes of the creatine kinase (CK) family--loci for brain (CKBB), muscle (CKMM), and mitochondrial (CKMT) forms--were studied by Southern filter hybridization analysis of DNAs isolated from a human x rodent somatic cell hybrid clone panel. Probes for the 3'-noncoding sequences of human CKBB and CKMM hybridized concordantly only to DNAs from somatic cell hybrids containing chromosomes 14 and 19, respectively. Thus the earlier assignment of the gene coding for the CKBB isozyme to chromosome 14 was confirmed by molecular means, as was the provisional assignment of CKMM to the long arm of chromosome 19. A probe containing canine sequences for CKMM cross-hybridized with human sequences on chromosomes 14 and 19, a result consistent with the assignments of CKBB and CKMM. A probe containing human sequences for CKMT enabled the provisional assignment of CKMT to human chromosome 15. Independent hybrids with portions of the long arm of chromosome 19 missing indicated the order of genes on the long arm of chromosome 19 as being cen-GPI-(TGFB, CYP1)-[CKMM, (APOC2-ERCC1)]-(CGB, FTL). The unexpectedly more distal location of APOC2 among the genes on the long arm--and APOC2's close association with CKMM--is discussed with respect to the close linkage relationship of APOC2 to myotonic muscular dystrophy.     

Linkage group VI of fish of the genus Xiphophorus (Poeciliidae): Assignment of genes coding for glutamine synthetase,uridine monophosphate kinase,and transferrin

Electrophoretic variation ascribable to three protein-coding loci, coding for glutamine synthetase (GS), uridine monophosphate kinase (UMPK), and transferrin (Tf), was observed in three species of fish of the genus Xiphophorus. Electrophoretic patterns in interspecific F1 hybrid heterozygotes suggested monomeric subunit structures of UMPK and Tf and a multimeric structure of undetermined subunit number of GS. Linkage analyses in backcross hybrids indicated a recombination map of GS-0%-Tf-10.8%-UMPK. This group (designated Xiphophorus linkage group VI) was shown to assort independently from the 14 enzyme loci assigned to linkage groups I-V and from 19 other informative markers within the limits of the data.     

Site-specific recombination of the tal-1 gene is a common occurrence in human T cell leukemia.

The tal-1 gene is altered as a consequence of the t(1;14) (p32;q11) chromosome translocation observed in 3% of patients with T cell acute lymphoblastic leukemia (T-ALL). tal-1 encodes a helix-loop-helix (HLH) domain, a DNA binding and dimerization motif found in a number of proteins involved in cell growth and differentiation. We now report that an additional 25% of T-ALL patients bear tal-1 gene rearrangements that are not detected by karyotype analysis. These rearrangements result from a precise 90 kb deletion (designated tald) that arises independently in different patients by site-specific DNA recombination. Since the deletion junctions resemble the coding joints of assembled immunoglobulin genes, tald rearrangements are likely to be mediated by aberrant activity of the immunoglobulin recombinase. Moreover, t(1;14)(p32;q11) translocations and tald rearrangements disrupt the coding potential of tal-1 in an equivalent manner, and thereby generate a common genetic lesion shared by a significant proportion of T-ALL patients.     

The tal gene undergoes chromosome translocation in T cell leukemia and potentially encodes a helix-loop-helix protein.

We have analyzed t(1;14)(p32;q11) chromosome translocations from two patients with T cell acute lymphocytic leukemia. The chromosome 1 breakpoints of these patients lie within a kilobasepair of each other, and thus define a genetic locus (designated tal) involved in T cell oncogenesis. Moreover, we have identified sequences within tal that potentially encode an amphipathic helix-loop-helix motif, a DNA-binding domain found in a variety of proteins that control cell growth and differentiation. The homology domain of tal is especially related to that of lyl-1, a gene on chromosome 19 that has also been implicated in T cell oncogenesis. Hence, tal and lyl-1 encode a distinct family of helix-loop-helix proteins involved in the malignant development of lymphocytes.     

Role for the Vacuolar H+-ATPase in Regulating the Cytoplasmic pH: An in Vivo Study Carried out in chl1, an Arabidopsis thaliana Mutant Impaired in NO-3 Transport

The effects of the growth in a medium containing NH₄NO₃ as nitrogensource were studied on cell sap pH, cytoplasmic pH and malatecontent in chl1, an Arabidopsis thaliana mutant impaired inchlorate and nitrate transport. In all the conditions testedthe pH of the cytoplasm in chl1 was more alkaline, and thatof the vacuole was more acidic as compared with those measuredin wt. Treatment with bafilomycin A1, a specific inhibitor ofthe vacuolar H⁺-ATPase, induced a small alkalinization of thevacuole, and a significant acidification of the cytoplasm, theseeffects being greater in chl1 than in wt. The greater responseof the mutant to bafilomycin Al suggests that, in the absenceof the inhibitor, the activity of the tonoplast H⁺-ATPase inchl1 is higher than in wt, this diversity being a possible reasonfor the differences in intracellular pH detected between thetwo strains. A possible role for the vacuolar H⁺-ATPase in regulatingthe cytoplasmic pH is discussed. (Received August 2, 1995; Accepted February 1, 1996)