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.     

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.     

The Gene Encoding the Catalytic Subunit Cα of cAMP-Dependent Protein Kinase (Locus PRKACA) Localizes to Human Chromosome Region 19p13.1

We have determined the chromosomal localization of the gene for the catalytic subunit Cα of cAMP-dependent protein kinase (locus PRKACA) to human chromosome 19 using polymerase chain reaction (PCR) and Southern blot analysis of two different somatic cell hybrid mapping panels. In addition, PCR analysis of a chromosome 19 mapping panel revealed the presence of a human Cα-specific amplification product only in cell lines containing the region 19p13.1 to 19q12. Finally, two-color fluorescencein situhybridization to metaphase chromosomes using the human Cα cDNA and human chromosome 19 inter-Alu-PCR product as probes localized the human Cα gene to chromosome region 19p13.1.     

Depolarization and Neurotransmitters Increase Neuronal Protein Tyrosine Phosphorylation

Abstract: In rat hippocampal slices and in neurons in primary culture, K⁺-induced depolarization increased markedly and rapidly tyrosine phosphorylation of a 110-kDa protein (pp110) and, to a lesser degree, of a 120-kDa protein (pp120), in a calcium-dependent fashion. Qlutamate, 1-aminocyclopentane- trans -1,3-dicarboxylic acid (an agonist of metabotropic glutamate receptors), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (an agonist of ionotropic glutamate receptors) stimulated also tyrosine phosphorylation of pp110 and pp120. These effects were not observed in astrocytes in primary culture. In hippocampal slices tyrosine phosphorylation of pp110 and pp120 was stimulated by Ca²⁺-ionophores and by phorbol esters and antagonized by a chelator of intracellular Ca²⁺and by drugs that inhibit protein kinase C. Stimulation of muscarinic and α₁,-adrenergic receptors increased also tyrosine phosphorylation of pp110 and pp120. These results demonstrate that membrane depolarization and stimulation of neurotransmitter receptors activate a tyrosine phosphorylation pathway in neurons. This pathway involves an increase in intracellular Ca²⁺ concentrations and the activation of protein kinase C. It may provide a biochemical basis for some neurotrophic effects of electrical activity and neurotransmitters and may contribute to the role of tyrosine phosphorylation in long-term potentiation.     

Three Linked Enzyme Loci in Fishes: Implications in the Evolution of Vertebrate Chromosomes

A three-point linkage group comprised of loci coding for adenosine deaminase (ADA), glucose-6-phosphate dehydrogenase (G6PDH), and 6-phosphogluconate dehydrogenase (6PGD) is described in fish of the genus Xiphophorus (Poeciliidae). The alleles at loci in this group were shown to assort independently from the alleles at three other loci—isocitrate dehydrogenase 1 and 2, and glyceraldehyde-3-phosphate dehydrogenase 1. Alleles at the latter three loci also assort independently from each other. Data were obtained by observing the segregation of electrophoretically variant alleles in reciprocal backcross hybrids derived from crosses between either X. helleri guentheri or X. h. strigatus and X. maculatus. The linkage component of χ² was significant (<0.01) in all crosses, indicating that the linkage group is conserved in all populations of both species of Xiphophorus examined. While data from X. h. guentheri backcrosses indicate the linkage relationship ADA—6%— G6PDH—24%—6PGD, and ADA—29%— 6PGD (30% when corrected for double cross-overs), data from backcrosses involving strigatus, while supporting the same gene order, yielded significantly different recombination frequencies. The likelihood of the difference being due to an inversion could not be separated from the possibility of a sex effect on recombination in the present data. The linkage of 6PGD and G6PDH has been shown to exist in species of at least three classes of vertebrates, indicating the possibility of evolutionary conservation of this linkage.