Mapping Approaches to Gene Identification in Humans

Although a number of human genes that cause disease have been traced through the defective product, most genetic defects are recognized only by phenotype. When the biochemical defect is unknown, a gene can be located only through molecular approaches based on coinheritance (genetic linkage) of the disease phenotype with a particular allele of a polymorphic DNA marker that has already been mapped to a specific chromosomal region. Linkage studies in affected families have already localized genes for several important diseases, including cystic fibrosis. Finding a genetic linkage in families in which a disease segregates requires that the human genetic map have a large number of polymorphic markers; when the map is dense enough, any disease gene can be located by linkage to a known marker. Many DNA segments with a high degree of polymorphism are being found and mapped as markers in normal reference pedigrees. Genetic linkage mapping has implications even broader than its application to prenatal diagnosis or therapeutic strategy; analyzing mutations in important genes will illuminate basic mechanisms in molecular biology and the early events that lead to cancer and other disorders.     

Plague Meningitis—A Retrospective Analysis of Cases Reported in the United States, 1970-1979

Meningitis caused by Yersinia pestis developed in 6 (6%) of a total of 105 patients with plague reported to the Centers for Disease Control from 1970 to 1979. Five of the six cases occurred in children aged 10 to 15 years. All six patients received antibiotic therapy before meningitis developed, which appeared between the 9th and 14th days after the onset of acute illness in five of the six patients. There were no neurologic sequelae. The antigenic and biochemical profiles of the Y pestis strains isolated from cerebrospinal fluid in the meningitis cases did not differ from those of the Y pestis strains obtained from blood and bubo aspirates in the other 99 patients, and neither did in vitro studies suggest antibiotic resistance. While plague meningitis is an uncommon complication of acute plague infection, physicians in the western United States should be aware that it may develop as much as 14 days after antibiotic therapy for the acute plague infection has been initiated.     

The mouse Fc receptor for IgG (Ly-17) : molecular cloning and specificity

A cDNA clone encoding the mouse Ly-17⁺ Fc receptor for IgG, isolated from a myelomonocytic cell line, was sequenced and expression of mRNA and the functional FcR investigated. The receptor is a 301 amino acid transmembrane glycoprotein with two homologous extracellular domains that are also homologous to members of the Ig superfamily. The receptor has four sites of N-linked glycosylation and a long 94 amino acid cytoplasmic tail. Northern analysis, immune complex binding, and serological studies demonstrate that the receptor encoded by the cDNA clone binds mouse IgG_1/2b and rabbit IgG complexes.     

Effect of gibberellic acid on pod set in soybean

Field-grown soybean plants (Glycine max (L.) Merr. cv. Evans) were treated with gibberellic acid (GA₃; 10gl^–1) and/or (2-chloroethyl)-trimethylammonium chloride (CCC; 0.8gl^–1) in 1983 and 1984, and subsequent anthesis, pod set, seed size, seed number, and seed yield were determined at one node. The treatments were applied to five leaves in the center of each plant (typically leaves 7–11) and reproductive development at the node in the center of those leaves was monitored. Gibberellin A₃ applied Early (about 3d before anthesis of the first flower at the monitored node) had no effect on the number of flowers produced, but decreased the fraction of flowers that set pods in both experimental years (by 32% in 1983 and 76% in 1984). Seed size was slightly decreased by the GA₃ treatment in 1983 but not in 1984. The Middle GA₃ treatment (applied about 3 days after the Early treatment) slightly decreased the number of pods set; and Late treatments (9 days after) had no effect. None of the monitored parameters were affected by CCC.The Early experiments were repeated with two additional genotypes, Lincoln and T210. Genotype T210 is a single-gene, dwarf mutant of Lincoln whose stem elongation and leaf expansion are insensitive to GA₃. Gibberellin A₃ affected the reproductive parameters in Lincoln very similarly to Evans but those in T210 were unaffected. This indicates that GA₃ exerts its effect by increasing the mass of vegetative tissue and thus diverting assimilates away from the pods. However, since the mutation in T210 might affect a receptor that is in flowers as well as shoots, it is possible that GA₃ exerted its effect on the normal genotypes directly on the developing pods, rather than indirectly by diverting photoassimilates.     

Transductional analysis of chromosome replication time

Summary Following transduction of exponentially growing cultures of Escherichia coli with phage P1, cells with recombinant phenotype begin to increase in number after an initial lag of about one generation time. We show that transductants for markers located at different positions on the chromosome begin to increse at different times, in reverse order to that in which they are replicated. The period over which this happens is equal in duration to the time taken to replicate the chromosome and we have used this relationship to calculate the C-period of E. coli K12 growing at 30°C. We exclude transduction-induced filamentation as the cause of the initial lag and suggest that the lag may result from the way in which donor DNA is inherited.     

Electrical Characteristics of the Tonoplast of Cham corallincr. A Study Using Permeabilised Cells

Use of permeabilised cells of Chara corallina provides a uniqueopportunity to study the electrical characteristics of the tonoplastwhilst being able to control ionic conditions on the outsideof the membrane. Current-voltage (I/V) analysis over wide voltagespans, and admittance measurements at 5 Hz showed that manypermeabilised cells had a similar conductance and capacitanceto the tonoplast of intact cells. Cells developed two regionsof negative-slope conductance upon addition of external Cl^–,which suggests the existence of potential-dependent Cl^–channels in the Chara tonoplast. With Cl^– concentrationssimilar to those expected in vivo, the resting potential wasmore sensitive to changes in external K⁺ than Cl^–; however,a decrease in external K⁺ did not significantly alter the shapeof the I/V relation. ¹Present address: Biopysics Laboratory, School of BiologicalSciences, A12, University of Sydney, Sydney, N.S.W., 2006, Australia ²Permanent address: Department of botany, Faculty of Science,University of Tokyo, Hongo, Tokyo 113, Japan (Received May 6, 1987; Accepted September 21, 1987)     

Polymorphism and Gene Conversion in Mouse α-Globin Haplotypes

We have cloned and characterized three distinct alpha-globin haplotypes obtained from inbred strains of the mouse, Mus domesticus. We report here the complete nucleotide sequence of the six alpha-globin genes that the haplotypes contain. Our analysis of these genes and those from one other previously described haplotype indicates that recurrent gene conversion events have played a major role in their history. The pattern of nucleotide substitutions suggests that conversions have occurred both within and between haplotypes. Limited segments of coding and noncoding DNA have been involved in these gene conversion events. In two of the haplotypes, the nonallelic genes of each maintain DNA sequence identity over discrete intervals and encode the same alpha-globin polypeptide. On the other hand, the coding regions of some genes have accumulated replacement changes that result in distinct alpha-globins. In one instance, these changes appear to reflect positive selection of advantageous mutations.     

Heparin potentiates the action of plasma membrane-associated growth stimulatory activity

Plasma membranes prepared from mouse liver have been previously shown to contain growth stimulatory activity as determined with cultured mouse fibroblasts. This growth stimulatory activity, termed plasma membrane-associated growth stimulatory activity (PMGA), is highly mitogenic in the presence of platelet-poor plasma. We now demonstrate that the growth stimulatory action of PMGA is dramatically enhanced by the addition of heparin. The half-maximal effect of heparin was observed at 1-3 micrograms/ml. The synergistic effect was seen in two distinct assays; the stimulation of DNA synthesis in quiescent cells, and an increase of cell number over a 3-day culture period. Heparin, by itself, does not have any measurable influence on the growth of fibroblasts. The action of heparin is not unique to this glycosaminoglycan, as several other highly sulfated polysaccharides, including dextran sulfate, pentosan polysulfate, and fucoidan, also exhibited the highly synergistic effect. Among other glycosaminoglycans examined, chondroitin sulfate B and heparan sulfate had a small, but significant, effect on enhancing the growth stimulatory action of PMGA. Chondroitin sulfate A, chondroitin sulfate C, hyaluronic acid dextran, and poly-L-glutamic acid, however, had no detectable effect. Further experiments suggested that the effect of heparin is twofold, namely, both a potentiation of growth stimulatory activity and a protection of PMGA activity. The data presented here suggest that the association of various cell surface components, such as PMGA and specific proteoglycans, can modulate the growth potential of a cell.     

Sterol Composition and Ecdysteroid Content of Eggs of the Root-knot Nematodes Meloidogyne incognita and M. arenaria

Free and esterified sterols of eggs of the root-knot nematodes Meloidogyne incognita races 2 and 3 and M. arenaria race 1 were isolated and identified by gas-liquid chromatography-mass spectrometry. The major sterols of eggs of each race were 24-ethylcholesterol (33.4-38.8% of total sterol), 24-ethylcholestanol (18.3-25.3%), 24-methylcholesterol (8.6-11.7%), 24-methylcholestanol (7.7-12.5%), and cholesterol (4.6-11.6%). Consequently, the major metabolic transformation performed by Meloidogyne females or eggs upon host sterols appeared to be saturation of the sterol nucleus. The free and esterified sterols of the same race did not differ appreciably, except for a slight enrichment of the steryl esters in cholesterol. Although the sterol composition of Meloidogyne eggs differed from that of other life stages of other genera of plant-parasitic nematodes, the three Meloidogyne races could not be distinguished from each other by their egg sterols. Ecdysteroids, compounds with hormonal function in insects, were not detected by radioimmunoassay in the Meloidogyne eggs either as free ecdysteroids or as polar conjugates.