Contraceptive potential of antibodies to the zona pellucida

The notion of a contraceptive vaccine based on gamete-specific surface antigens was first proposed over a decade ago, as the result of in-vitro and in-vivo studies, and in recent years has been the subject of intensive research. In particular, the zona pellucida has attracted much attention as a potential target for immunological intervention in the fertilization process. Such is the rapidly-expanding nature of research into the biochemical and biological characterization of this structure, that a review of the implications for the development of a contraceptive vaccine seems timely.     

Mutagenicity of bi-, tri- and tetra-cyclic aromatic hydrocarbons in the "taped-plate assay" and in the conventional salmonella mutagenicity assay

Aromatic hydrocarbons in the range of 1-4 nuclear rings were examined for mutagenicity in the so-called "taped-plate assay". This modification of the Ames assay is particularly equipped for the detection of volatile mutagens. Of the many compounds tested only phenanthrene, pyrene, benzo[c]phenanthrene and benzoacenaphthylene were positive in this assay. The present data underline the exceptional behaviour of fluoranthene by being a rather potent bacterial mutagen with a volatile nature (as found in a previous study).     

Genome instability in interspecific cell hybrids I. Unstable expression of genes in divergent cell hybrids

Somatic cell hybrids between cells of widely divergent mammalian species display a range of chromosomal and genetic anomalies which may be the equivalent of the “genomic shock” phenomena observed in many plant and animal interspecific hybrids. Mouse-kangaroo hybrids show extreme segregation and fragmentation of the kangaroo chromosomes. Here 1 show that, in addition to the chromosomal instability, some hybrids display unstable expression of three genes borne on the kangaroo active maternal X chromosome. These genes (HPRT, G6PD andPGK) may be co-ordinately inactivated at high frequency, then reactivated once more. I suggest that this reversible inactivation in interspecific hybrids may be the result of an unstable change at an X inactivation centre located in the kangaroo X_q.     

Images of purple membrane at 2.8 A resolution obtained by cryo-electron microscopy

Improvements in technique have produced electron micrographs of purple membrane that provide, after computer analysis, reproducibly measurable diffraction peaks extending to 2.8 A (1 A = 0.1 nm). The improvements include better specimen preparation, a more stable cryo-electron microscope with better alignment and the addition of an image-processing step, which gives weights to local areas of the image according to the local strength of the periodic component of the image. These improvements have enabled the calculation of a directly phased projection map at 2.8 A resolution.     

Clinical skills of medical residents: a review of physical examination.

Students are introduced to techniques of physical examination at medical school. However, their skills are deficient at the time of graduation, and with the increasing shift of clinical teaching away from the bedside and into the conference room it is expected that these skills will weaken in succeeding generations of physicians. A practical and satisfactory method of addressing this problem during internship and residency training has not been forthcoming because of the lack of a regular forum for the teaching of clinical skills in busy tertiary referral hospitals and the shortage of teachers with the necessary skills and commitment to teaching a large number of house staff. We describe a program whose unique hierarchical approach has permitted a detailed ongoing review of physical examination. One clinician was able to teach 24 residents by instructing a small group of senior residents, who in turn, after practising with clinical clerks, taught groups of junior residents.     

Nucleolytic action of chondroitinase ABC on the lumbar disc of the rabbit

Nucleolysis using chondroitinase ABC was studied using the rabbit's intervertebral lumbar disc. The purpose was to find a possible alternative to chymopapain which is commonly used in the management of sciatica due to disc herniation. The injection of 1 U of the enzyme into the nucleus pulposus gave significant histological and biochemical changes in all twelve discs studied.     

Neural function: metabolism and actions of inositol metabolites in mammalian brain

In the nervous system, a variety of cell types respond to external stimuli through the inositol lipid signalling pathways. The stimulus-coupled sequence of intracellular events has been investigated in a homogeneous model system, the cloned mammalian neural cell line NG115-401L. The neural peptide bradykinin stimulates a rapid production of identified inositol phosphate isomers and an intracellular Ca2+ discharge followed by a persistent plasma membrane influx. The temporal sequence suggests that Ins(1,4,5)P3 or Ins(1,3,4,5)P4 or both may coordinate these events in a neuronal cell, as has been suggested in other cell types. Thapsigargin, an irritant and tumour-promoting plant product, produces calcium transients in the absence of inositol phosphate production, and may provide a new tool for investigating the interactions between inositol phosphates and changes in cellular calcium homeostasis. In the 401L line, high levels of radiolabelled InsP5 and InsP6 have been detected, which has led to the evaluation of their possible occurrence and actions in normal brain. Both InsP5 and InsP6 are produced from a radiolabelled myo-inositol precursor in intact mature brain in a region-specific manner. This suggests that both inositol polyphosphates may be end products of regionally regulated biosynthetic pathways. When microinjected into a nucleus of the brainstem, or iontophoretically applied to the dorsal horn of the spinal cord, both InsP5 and InsP6, but not Ins(1,3,4,5)P4 isomers, appear to be potent neural stimulants. These results suggest that the inositol lipid signalling pathways may generate both intracellular and extracellular signals in brain.     

Formation of novel hairpin structures by telomeric C-strand oligonucleotides.

Telomeres are specialized structures at the ends of chromosomes that are required for long term chromosome stability and replication of the chromosomal terminus. Telomeric DNA consists of simple repetitive sequences with one strand G-rich relative to the other, C-rich, strand. Evolutionary conservation of this feature of telomeric repeat sequences suggests that they have specific structural characteristics involved in telomere function. Absorbance thermal denaturation, chemical modification and non-denaturing gel electrophoretic analyses showed that telomeric C-strand oligonucleotides form stable non-Watson-Crick hairpin structures containing C.C+ base pairs. Formation of such hairpins may facilitate previously reported G-strand exclusive interactions.     

The I-CeuI endonuclease recognizes a sequence of 19 base pairs and preferentially cleaves the coding strand of the Chlamydomonas moewusii chloroplast large subunit rRNA gene.

The I-CeuI endonuclease is a member of the growing family of homing endonucleases that catalyse mobility of group I introns by making a double-strand break at the homing site of these introns in cognate intronless alleles during genetic crosses. In a previous study, we have shown that a short DNA fragment of 26 bp, encompassing the homing site of the fifth intron in the Chlamydomonas eugametos chloroplast large subunit rRNA gene (Ce LSU.5), was sufficient for I-CeuI recognition and cleavage. Here, we report the recognition sequence of the I-CeuI endonuclease, as determined by random mutagenesis of nucleotide positions adjacent to the I-CeuI cleavage site. Single-base substitutions that completely abolish endonuclease activity delimit a 15-bp sequence whereas those that reduce the cleavage rate define a 19-bp sequence that extends from position -7 to position +12 with respect to the Ce LSU.5 intron insertion site. As the other homing endonucleases that have been studied so far, the I-CeuI endonuclease recognizes a non-symmetric degenerate sequence. The top strand of the recognition sequence is preferred for I-CeuI cleavage and the bottom strand most likely determines the rate of double-strand breaks.     

Statistical analysis of in situ hybridization data: Derivation and use of the Zmax test

There are many situations in which grain distributions resulting from in situ hybridization of radioactively labeled probes to unique genes should be subjected to a statistical analysis. However, the problems posed by analysis of in situ hybridization data are not straightforward, and no completely satisfying method is currently available. We have developed a procedure in which the major and any number of minor site(s) of hybridization may be specifically located and the significance of each tested. This Z_max procedure first tests the overall distribution for departure from randomness and then identifies significantly overlabeled whole chromosomes (or chromosome arms or other large segments), a process that may be repeated to pinpoint significantly overlabeled regions within these chromosomes. We describe in detail the derivation of the Z_max statistic, present tables of significant Z_max levels, and show with examples how Z_max is used in tests of significance of in situ hybridization data.