Presynaptic effectors contributing to cAMP-induced synaptic potentiation in Drosophila

cAMP analogs and activation of adenylyl cyclase by forskolin strongly potentiate synaptic transmission at the Drosophila neuromuscular junction. These effects are generally attributed to activation of cAMP-dependent protein kinase. Recent reports on crustacean and mammalian synapses have implicated other cAMP-dependent effectors in synaptic potentiation. Drosophila neuromuscular junctions were tested for effects of two known cAMP-dependent effectors: hyperpolarization-activated, cyclic nucleotide-regulated channels (HCNCs) and guanine nucleotide exchange protein activated by cAMP (Epac). Forskolin-induced enhancement of synaptic transmission was drastically reduced by a blocker of HCNCs, but not completely eliminated. A specific agonist for Epac modestly enhanced synaptic potentials. This agonist also stabilized their amplitudes in the presence of a blocker of HCNCs. The observations implicate HCNCs and Epac in cAMP-dependent potentiation that does not require cAMP-dependent protein kinase, indicating that additional previously unexplored factors contribute to synaptic plasticity in Drosophila. Genetic and molecular techniques available for Drosophila can be used to define the underlying molecular basis for cAMP-dependent synaptic potentiation.     

The regulation of mitochondrial DNA copy number in glioblastoma cells

As stem cells undergo differentiation, mitochondrial DNA (mtDNA) copy number is strictly regulated in order that specialized cells can generate appropriate levels of adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS) to undertake their specific functions. It is not understood whether tumor-initiating cells regulate their mtDNA in a similar manner or whether mtDNA is essential for tumorigenesis. We show that human neural stem cells (hNSCs) increased their mtDNA content during differentiation in a process that was mediated by a synergistic relationship between the nuclear and mitochondrial genomes and results in increased respiratory capacity. Differentiating multipotent glioblastoma cells failed to match the expansion in mtDNA copy number, patterns of gene expression and increased respiratory capacity observed in hNSCs. Partial depletion of glioblastoma cell mtDNA rescued mtDNA replication events and enhanced cell differentiation. However, prolonged depletion resulted in impaired mtDNA replication, reduced proliferation and induced the expression of early developmental and pro-survival markers including POU class 5 homeobox 1 (OCT4) and sonic hedgehog (SHH). The transfer of glioblastoma cells depleted to varying degrees of their mtDNA content into immunocompromised mice resulted in tumors requiring significantly longer to form compared with non-depleted cells. The number of tumors formed and the time to tumor formation was relative to the degree of mtDNA depletion. The tumors derived from mtDNA depleted glioblastoma cells recovered their mtDNA copy number as part of the tumor formation process. These outcomes demonstrate the importance of mtDNA to the initiation and maintenance of tumorigenesis in glioblastoma multiforme.     

Peripheral generation and modulation of crustacean motor axon activity at high temperatures

Summary We have examined the effects of temperature changes on the stretcher muscle and its motor supply in a crab (Pachygrapsus crassipes). An increase in temperature caused a decrease in the amplitude of evoked excitatory junctional potentials (ejp's). Above a critical threshold a single action potential in the excitor (E) or specific inhibitor (SI) axon provoked multiple spikes in the appropriate axon and concomitant ejp's or inhibitory junctional potentials (ijp's) in the stretcher muscle fibers. The critical temperature for generation of peripheral spikes was dependent upon the crab's thermal history.In preparations in which a shock to the E axon evoked repetitive firing, stimulation of the SI axon at about the same time as the E axon abolished or curtailed the peripherally generated E axon responses. No reciprocal modulation of SI activity by the E axon was observed. GABA abolished the peripheral generation of E spikes and picrotoxin prevented SI modulation of E activity. We suggest that the site of SI modulation is at the axo-axonal synapses, possibly at the fine E axon branches and the bottlenecks along the E axon where inhibitory synapses have been observed.Abbreviations CI common inhibitor (axon) - E excitor (axon) - ejp excitatory junctional potential - ijp inhibitory junctional potential - SI specific inhibitor axon This work was supported by grants awarded to Dr. Atwood from the National Research Council of Canada and the Muscular Dystrophy Association of Canada.     

A second locus for familial high myopia maps to chromosome 12q.

Myopia, or nearsightedness, is the most common eye disorder worldwide. "Pathologic" high myopia, or myopia of <=-6.00 diopters, predisposes individuals to retinal detachment, macular degeneration, cataract, or glaucoma. A locus for autosomal dominant pathologic high myopia has been mapped to 18p11.31. We now report significant linkage of high myopia to a second locus at the 12q21-23 region in a large German/Italian family. The family had no clinical evidence of connective-tissue abnormalities or glaucoma. The average age at diagnosis of myopia was 5.9 years. The average spherical-component refractive error for the affected individuals was -9.47 diopters. Markers flanking or intragenic to the genes for the 18p locus, Stickler syndromes type I and II (12q13.1-q13.3 and 6p21.3), Marfan syndrome (15q21.1), and juvenile glaucoma (chromosome 1q21-q31) showed no linkage to the myopia in this family. The maximum LOD score with two-point linkage analysis in this pedigree was 3.85 at a recombination fraction of .0010, for markers D12S1706 and D12S327. Recombination events identified markers D12S1684 and D12S1605 as flanking markers that define a 30.1-cM interval on chromosome 12q21-23, for the second myopia gene. These results confirm genetic heterogeneity of myopia. The identification of this gene may provide insight into the pathophysiology of myopia and eye development.     

Variation in ribosomal RNA gene number in mouse chromosomes

Hybridization of 125-I-ribosomal RNA to mouse chromosomes in situ produced significant differences in grain count at known rDNA sites, depending on the strains from which they were derived. This is interpreted to mean that the number of rRNA genes in a given nucleolar chromosome, and in the entire genome, is polymorphic among strains and among outbred individuals.     

Localization of rDNA in the chimpanzee (Pan troglodytes) chromosome complement

In situ hybridization was used to identify the sites of rDNA in the chromosome complement of the chimpanzee (Pan troglodytes). The rDNA was present in the satellite regions of chimpanzee chromosomes 14, 15, 17, 22 and 23. Four of these (14, 15, 22, 23) are homologous to human chromosomes carrying rDNA: 13, 14, 21 and 22.     

The chromosomal location of ribosomal DNA in the mouse

In situ hybridization of I¹²⁵-labelled ribosomal RNA to mouse chromosomes was used to determine the location of the rDNA loci. The results demonstrate the presence of rDNA sites on chromosomes 15, 18 and 19.