Cholesterol Synthesis and Nerve Regeneration

Abstract: In this report, we examine the requirement of cholesterol biosynthesis and its axonal transport for goldfish optic nerve regeneration. Cholesterol, labeled by intraocular injection of [³H]mevalonolactone. exhibited a delayed appearance in the optic tectum. Squalene and other minor components were labeled but not transported. Following optic nerve crush, the amount of labeled cholesterol transport was elevated, while retinal labeling was not altered relative to control fish. A requirement for cholesterol biosynthesis is inferred from the inhibition of neurite outgrowth in retinal explants caused by the cholesterol synthesis inhibitor, 20, 25-diazacholes-terol. The inhibition of growth could be overcome by addition of mevalonolactone, but not cholesterol, to the medium. Intraperitoneal administration of 200 nmol of dia-zacholesterol resulted in 92-98% inhibition of retinal cholesterol synthesis and accumulation of labeled des-mosterol and other lipids in fish retina and brain which persisted for 2 weeks. Diazacholesterol-treated fish showed no reduction in the amount of lipid-soluble radioactivity transported following intraocular injection of [³H]mevalonolactone, but there were alterations in the chromatographic pattern of the transported labeled lipids. In contrast to its effects on neurite outgrowth in vitro , diazacholesterol did not inhibit optic nerve regeneration in vivo , as measured both by arrival of labeled rapidly transported protein at the tectum and by time required for the return of visual function.     

Mitochondrial DNA polymorphism and phylogenetic relationships inHevea brasiliensis

Using fourteen random mitochondrial DNA probes, we have examined restriction fragment length polymorphism (RFLP) in wild and cultivatedHevea brasiliensis. A total of 395 accessions, including 345 from various prospectings collected in Brazil, Colombia and Peru and 50 cultivated clones, were analyzed. Two other species (H. benthamiana andH. pauciflora) were also included in the study for comparison. The high level of mitochondrial polymorphism allowed us to divide all the accessions analyzed into 212 distinct genotypes. The genetic variability of cultivated clones was limited to four genotypes forming two clusters. In contrast, considerable genetic variation was found in the wild collections. In almost all cases, accessions displaying the same RFLP profile were restricted to the same geographical area (same or neighbor administrative districts). In addition, accessions whose genetic closeness was predicted by RFLP profiles were also clustered according to geographical origin. In a few cases, however, similar RFLP profiles were found for accessions originating from geographically distant districts. This discrepancy can be explained either by seed dispersion (by river) or possibly by similar genetic events occurring independently in different geographical locations. Chloroplast DNA RFLP was also analyzed in 217 accessions, representative of 126 distinct mitochondrial genotypes. Very few differences were found, indicating that the chloroplast genome is more highly conserved than the mitochondrial genome.     

Elongation of the First Internode of the Pea Seedling during Etiolation : Interaction of Environment and Genotype

In the present study, 40 lines of peas, Pisum sativum L., from the Weibullsholm collection were examined for elongation response of the first internode to growth in soil, sand, or in darkness in air. The results obtained establish that appearance of the first (lowest) node of the epicotyl at the surface of soil was usual in only a few of the lines tested (L25, L1088, L1570). By contrast, appearance of the first node at the surface of sand as a result of enhancement of first internode extension occurred in 80% of the lines tested. In many lines, extension in sand or soil was more than in darkness in air, a surprising observation given that the known response of the pea epicotyl to pressure is to produce the extension inhibitor, ethylene. Results of two crosses, one of tall×dwarf and one of tall×tall, point to the conclusion that the Le/le locus exercises only partial control over first internode extension and that other, as yet unknown, loci are implicated.     

Erythroid and granulocytic colony growth in cultures supplemented with human serum lipoproteins.

The ability of human serum to support erythroid and granulocytic colony formation has been investigated. It was found that normal human serum could replace fetal calf serum in the cultures and was able to support the growth of these hemopoietic colonies. Serum fractions enriched for low density lipoproteins, either by precipitation with Heparin-Mn++ or by ultracentrifugation, was found to contain this growth supporting activity of human serum.     

Existence of Three Subtypes of Bradykinin B2 Receptors in Guinea Pig

We describe the binding of [3H]bradykinin to homogenates of guinea pig brain, lung, and ileum. Analysis of [3H]bradykinin binding kinetics in guinea pig brain, lung, and ileum suggests the existence of two binding sites in each tissue. The finding of two binding sites for [3H]bradykinin in ileum, lung, and brain was further supported by Scatchard analysis of equilibrium binding in each tissue. [3H]Bradykinin binds to a high-affinity site in brain, lung, and ileum (KD = 70-200 pM), which constitutes approximately 20% of the bradykinin binding, and to a second, lower-affinity site (0.63-0.95 nM), which constitutes the remaining 80% of binding. Displacement studies with various bradykinin analogues led us to subdivide the high- and lower-affinity sites in each tissue and to suggest the existence of three subtypes of B2 receptors in the guinea pig, which we classify as B2a, B2b, and B2c. Binding of [3H]bradykinin is largely to a B2b receptor subtype, which constitutes the majority of binding in brain, lung, and ileum and represents the lower-affinity site in our binding studies. Receptor subtype B2c constitutes approximately 20% of binding sites in the brain and lung and is equivalent to the high-affinity site in brain and lung. We suggest that a third subtype of B2 receptor (high-affinity site in ileum), B2a, is found only in the ileum. All three subtypes of B2 receptors display a high affinity for bradykinin, whereas they show different affinities for various bradykinin analogues displaying agonist or antagonist activities.(ABSTRACT TRUNCATED AT 250 WORDS)     

Arterial supply and venous drainage of the brain of the black bear (Ursus americanus). I. Gross anatomical distribution

A morphological study of the intracranial vessels of the Black bear (Ursus americanus) was undertaken. The object was to provide basic information related to the vascular pattern in these animals as compared with other carnivores and with the human. Vascular casts were prepared from 6 animals. The vasculature of the brain disclosed patterns comparable to other species previously studied.     

Snx3 Regulates Recycling of the Transferrin Receptor and Iron Assimilation

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Highlights? Snx3 is highly expressed in vertebrate hematopoietic tissues ? Silencing of Snx3 results in anemia and hemoglobin defects in vertebrates ? Snx3 and Vps35 physically interact with Tfrc ? Snx3 is required for endosomal recycling of Tf-Tfrc complex     

Ciprofloxacin is an inhibitor of the Mcm2-7 replicative helicase

Most currently available small molecule inhibitors of DNA replication lack enzymatic specificity, resulting in deleterious side effects during use in cancer chemotherapy and limited experimental usefulness as mechanistic tools to study DNA replication. Towards development of targeted replication inhibitors, we have focused on Mcm2-7 (minichromosome maintenance protein 2–7), a highly conserved helicase and key regulatory component of eukaryotic DNA replication. Unexpectedly we found that the fluoroquinolone antibiotic ciprofloxacin preferentially inhibits Mcm2-7. Ciprofloxacin blocks the DNA helicase activity of Mcm2-7 at concentrations that have little effect on other tested helicases and prevents the proliferation of both yeast and human cells at concentrations similar to those that inhibit DNA unwinding. Moreover, a previously characterized mcm mutant (mcm4chaos3) exhibits increased ciprofloxacin resistance. To identify more potent Mcm2-7 inhibitors, we screened molecules that are structurally related to ciprofloxacin and identified several that compromise the Mcm2-7 helicase activity at lower concentrations. Our results indicate that ciprofloxacin targets Mcm2-7 in vitro, and support the feasibility of developing specific quinolone-based inhibitors of Mcm2-7 for therapeutic and experimental applications.