Effect of aluminium on iron uptake and transferrin-receptor expression by human erythroleukaemia K562 cells.

Incubation of human erythroleukaemia K562 cells with Al-transferrin inhibited iron uptake from 59Fe-transferrin by about 80%. The inhibition was greater than that produced by a similar quantity of Fe-transferrin. Preincubation of cells for 6 h with either Al-transferrin or Fe-transferrin diminished the number of surface transferrin receptors by about 40% compared with cells preincubated with apo-transferrin. Al-transferrin did not compete significantly with Fe-transferrin for transferrin receptors and, when cells were preincubated for 15 min instead of 6 h, the inhibitory effect of Al-transferrin on receptor expression was lost. Both forms of transferrin also decreased the level of transferrin receptor mRNA by about 50%, suggesting a common regulatory mechanism. Aluminium citrate had no effect on iron uptake or transferrin-receptor expression. AlCl3 also had no effect on transferrin-receptor expression, but at high concentration it caused an increase in iron uptake by an unknown, possibly non-specific, mechanism. Neither Al-transferrin nor AlCl3 caused a significant change in cell proliferation. It is proposed that aluminium, when bound to transferrin, inhibits iron uptake partly by down-regulating transferrin-receptor expression and partly by interfering with intracellular release of iron from transferrin.     

Genetic heterogeneity in X-linked hydrocephalus: linkage to markers within Xq27.3.

X-linked hydrocephalus is a well-defined disorder which accounts for > or = 7% of hydrocephalus in males. Pathologically, the condition is characterized by stenosis or obliteration of the aqueduct of Sylvius. Previous genetic linkage studies have suggested the likelihood of genetic homogeneity for this condition, with close linkage to the DXS52 and F8C markers in Xq28. We have investigated a family with typical X-linked aqueductal stenosis, in which no linkage to these markers was present. In this family, close linkage was established to the DXS548 and FRAXA loci in Xq27.3. Our findings demonstrate that X-linked aqueductal stenosis may result from mutations at two different loci on the X chromosome. Caution is indicated in using linkage for the prenatal diagnosis of X-linked hydrocephalus.     

Mutations in somePolycomb group genes ofDrosophila interfere with regulation of segmentation genes

Mutations in severalPolycomb (Pc) group genes cause maternal-effect or zygotic segmentation defects, suggesting thatPc group genes may regulate the segmentation genes ofDrosophila. We show that individuals doubly heterozygous for mutations inpolyhomeotic and six otherPc group genes show gap, pair rule, and segment polarity segmentation defects. We examined double heterozygous combinations ofPc group and segmentation mutations for enhancement of adult and embryonic segmentation defects.Posterior sex combs andpolyhomeotic interact withKrüppel ² and enhance embryonic phenotypes ofhunchback andknirps, andpolyhomeotic enhanceseven-skipped. Surprisingly, flies carrying duplications ofextra sex combs (esc), that were heterozygous for mutations ofeven-skipped (eve), were extremely subvital. Embryos and surviving adults of this genotype showed strong segmentation defects in even-numbered segments. Antibody studies confirm that expression ofeve is suppressed by duplications ofesc. However,esc duplications have no effect on other gap or pair rule genes tested. To our knowledge, this is only the second triplo-abnormal phenotype associated withPc group genes. Duplications of nine otherPc group genes have no detectable effect oneve. Expression ofengrailed (en) was abnormal in the central nervous systems of mostPc group mutants. These results support a role forPc genes in regulation of some segmentation genes, and suggest thatesc may act differently from otherPc group genes.     

Epidermal growth factor stimulates vascular endothelial growth factor production by human malignant glioma cells: a model of glioblastoma multiforme pathophysiology.

Hypervascularity, focal necrosis, persistent cerebral edema, and rapid cellular proliferation are key histopathologic features of glioblastoma multiforme (GBM), the most common and malignant of human brain tumors. By immunoperoxidase and immunofluorescence, we definitively have demonstrated the presence of vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFr) in five out of five human glioma cell lines (U-251MG, U-105MG, D-65MG, D-54MG, and CH-235MG) and in eight human GBM tumor surgical specimens. In vitro experiments with glioma cell lines revealed a consistent and reliable relation between EGFr activation and VEGF production; namely, EGF (1-20 ng/ml) stimulation of glioma cells resulted in a 25-125% increase in secretion of bioactive VEGF. Conditioned media (CM) prepared from EGF-stimulated glioma cell lines produced significant increases in cytosolic free intracellular concentrations of Ca2+ ([Ca2+]i) in human umbilical vein endothelial cells (HUVECs). Neither EGF alone or CM from glioma cultures prepared in the absence of EGF induced [Ca2+]i increases in HUVECs. Preincubation of glioma CM with A4.6.1, a monoclonal antibody to VEGF, completely abolished VEGF-mediated [Ca2+]i transients in HUVECs. Likewise, induction by glioma-derived CM of von Willebrand factor release from HUVECs was completely blocked by A4.6.1 pretreatment. These observations provide a key link in understanding the basic cellular pathophysiology of GBM tumor angiogenesis, increased vascular permeability, and cellular proliferation. Specifically, EGF activation of EGFr expressed on glioma cells leads to enhanced secretion of VEGF by glioma cells. VEGF released by glioma cells in situ most likely accounts for pathognomonic histopathologic and clinical features of GBM tumors in patients, including striking tumor angiogenesis, increased cerebral edema and hypercoagulability manifesting as focal tumor necrosis, deep vein thrombosis, or pulmonary embolism.     

Eavesdropping by Bats: The Influence of Echolocation Call Design and Foraging Strategy

We used playback presentations to free-flying bats of 3 species to assess the influence of echolocation call design and foraging strategy on the role of echolocation calls in communication. Near feeding sites over water, Myotis lucifugus and M. yumanensis responded positively only to echolocation calls of conspecifics. Near roosts, these bats did not respond before young of the year became volant, and after this responded to presentations of echolocation calls of similar and dissimilar design. At feeding sites Lasiurus borealis responded only to echolocation calls of conspecifics and particularly to “feeding buzzes”. While Myotis, particularly subadults, appear to use the echolocation calls of conspecifics to locate feeding sites, L. borealis appears to use the calls of a foraging neighbour attacking prey to identify opportunities for ‘stealing’ food.     

A rat homolog of the mouse deafness mutant jerker (je)

An autosomal recessive deafness mutant was discovered in our colony of Zucker (ZUC) rats. These mutants behave like shaker-waltzer deafness mutants, and their inner ear pathology classifies them among neuroepithelial degeneration type of deafness mutants. To determine whether this rat deafness mutation (−) defines a unique locus or one that has been previously described, we mapped its chromosomal location. F₂ progeny of (Pbrc:ZUC × BN/Crl) A/a B/b H/h+/− F₁ rats were scored for coat color and behavioral phenotypes. Segregation analysis indicated that the deafness locus might be loosely linked with B on rat Chromosome (Chr) 5 (RNO5). Therefore, 40 −/− rats were scored for BN and ZUC alleles at four additional loci, D5Mit11, D5Mit13, Oprd1, and Gnb1, known to map to RNO5 or its homolog, mouse Chr 4 (MMU4). Linkage analysis established the gene order (cM distance) as D5Mit11–(19.3)–B–(17.9)–D5Mit13–(19.2)–Oprd1–(21.5) − (1.2) Gnb1, placing the deafness locus on distal RNO5. The position of the deafness locus on RNO5 is similar to that ofjerker (je) on MMU4; the phenotypes and patterns of inheritance of the deafness mutation and je are also similar. It seems likely that the mutation affects the rat homolog of je. The rat deafness locus should, therefore, be named jerker and assigned the gene symbol Je. Received: 13 June 1995 / Accepted: 4 January 1996     

Prenatal diagnosis of cystic fibrosis by assay of amniotic fluid microvillar enzymes

Summary Activities of the microvillar enzymes -glutamyl-transpeptidase (GGTP), aminopeptidase M (APM), phosphodiesterase and maltase have been examined in second-trimester amniotic fluid as possible aids to the early prenatal diagnosis of cystic fibrosis (CF). The two peptidases, GGTP and APM, gave best results. If the fifth percentile of the normal range is used as an action line, the sensitivity of a positive test (low GGTP value) is 78% and the predictability 84%. At the tenth percentile the sensitivity is 100% and the predictability 77%. These approximate figures apply only to pregnancies where there has been a previous affected child. Until the primary protein defect in CF is discovered, this may prove an acceptable form of prenatal diagnosis to the high-risk mother.     

Amorphous ferrous sulfide as a reducing agent for culture of anaerobes.

Amorphous ferrous sulfide, prepared by reacting ferrous ammonium sulfate and sodium sulfide, is an excellent reducing agent for the culture of anaerobes. It reduces resazurin and reacts much more rapidly with O2 than does either soluble sulfide (HS)- or cysteine. One of the end products of the oxidation of ferrous sulfide with O2 is red and serves as an indicator for the oxygen contamination of a culture medium. Amorphous ferrous sulfide served as a suitable reducing agent for the growth of species of Methanobacterium or Clostridium. Its use is recommended for enrichment or culture of anaerobes (e.g. autotrophs, fermentative organisms) from sediments and other habitats were organic reducing agents are undesirable and where soluble sulfide might be toxic.