Search PubMed⌕ Search

Biomedical subjects

M H Johnson

Publications and source records attributed to M H Johnson.

At least 163 records · Page 9Linked to original sources
PubMed1992

Reliability of detection by polymerase chain reaction of the sickle cell-containing region of the beta-globin gene in single human blastomeres.

Human preimplantation embryos at various stages of development have been analysed using the polymerase chain reaction to amplify a 680 base pair fragment of the beta-globin gene. Successful amplification was achieved more frequently with DNA from intact embryos containing between one and 11 cells, single cumulus cells, oocytes which had failed to fertilize and polar bodies than from single blastomeres disaggregated from intact embryos and treated in an identical manner. The distribution of nuclei demonstrated using the nuclear chromophore diamino-phenyl-indole showed considerable inter-blastomere variation; however, no clear correlation between staining pattern and successful amplification was observed. The reason for the unreliable amplification of DNA from single blastomeres is unclear but this finding has important implications for preimplantation diagnosis of genetic disease.

Blastomeres↗
PubMed1992

Gene activity and cleavage arrest in human pre-embryos.

There is a high rate of spontaneous cleavage arrest around the four- to eight-cell stage of human development in vitro. Since this coincides with the time of activation of the embryonic genome it has been suggested that cleavage arrest may occur as a consequence of failure of gene activation. Gene expression in human pre-embryos is associated with an alpha-amanitin sensitive, qualitative change in protein synthesis. In order to ascertain the role of gene expression in cleavage arrest, we have examined the protein synthetic patterns of human pre-embryos which have undergone spontaneous cleavage arrest in vitro. Of 54 cleavage-arrested embryos, 27 demonstrated evidence of synthesis of proteins sensitive to alpha-amanitin, suggesting that cleavage arrest is not always accompanied by failure of activation of the genome. Our results would also suggest that activation of gene expression is simply related to neither cell number nor time spent in culture since fertilization, but may be related to continuing karyokinesis.

Amanitins↗
PubMed1992

Quantitative analysis of cellular glutathione in early preimplantation mouse embryos developing in vivo and in vitro.

The relative levels of reduced glutathione (GSH) have been measured fluorimetrically in individual eggs and early embryos from two mouse strains, one of which shows developmental arrest in vitro. GSH levels fell by approximately 20-25% at fertilization and by approximately 45% by the late 2-cell and early 4-cell stages. No differences were observed between strains or between embryos cultured in vitro or in vivo. Addition of exogenous H2O2 or diethylmaleate depleted GSH. GSH levels were not affected significantly after inhibition of GSH-peroxidase by mercaptosuccinate nor of catalase by aminotriazole. Mercaptosuccinate did not inhibit development but catalase inhibition caused arrest at the 2-cell stage. Addition of exogenous GSH or thioredoxin did not promote development of 'blocking' embryos through the 2-cell block. It is concluded that early embryos lack a mercaptosuccinate sensitive peroxidase activity for removing H2O2, which may be removed by catalase or the glutathione-S-transferase system. It is suggested that GSH may have a role in detoxifying peroxidated lipids. The results are consistent with a role for reactive oxygen species in the 2-cell block.

Amitrole↗
PubMed1992

Can the mouse embryo provide a good model for the study of abnormal cellular development seen in human embryos?

Mouse 2-cell embryos arrested in development, either due to the effect of in vitro culture conditions ('2-cell block') or after exposure to the protein synthesis inhibitor anisomycin, were examined to determine the effect of the level of protein synthesis on development. The rate of protein synthesis was found directly to reflect the developmental potential of the embryos. Embryos cultured in the highest dose of the drug failed to divide and had the lowest rate of protein synthesis over the period of investigation, whereas untreated viable 2-cell embryos in the control group had the highest rate of protein synthesis and developed normally. Measurement of the nuclear DNA showed that both arrested and non-arrested embryonic cells completed DNA replication. Furthermore, drug-arrested embryos, like embryos which 'block' in culture, remained morphologically intact when left in culture. Disruption of the nuclear integrity and formation of micronuclei, as is frequently observed in arrested human embryos, was not seen in mouse embryos. These results indicate that developmentally arrested mouse embryos may not be a good model for studying cellular dysfunction in early human development. Experimentation using human material is required to address directly the problem of abnormal human development.

Animals↗
PubMed1992

Can autism be predicted on the basis of infant screening tests?

The authors examined infant hearing and vision screening tests for a group of children subsequently diagnosed as autistic and compared them with a group of children suffering from non-specific developmental delay, as well as with a random sample of records. Four categories (motor, vision, hearing and language, social) were investigated at three ages: six, 12 and 18 months. The random sample group had a low incidence of reported problems at all ages. The learning-disabled group had a sharp increase in reported abnormalities in all categories at 12 months. The autistic group had a selective increase in the social category alone at 18 months.

Autistic Disorder↗
PubMed1992

Cochlear implants in children: reliability of computed tomography.

Preoperative temporal bone computed tomography (CT) can demonstrate anatomic details relevant to surgical management and is therefore essential in the presurgical evaluation of patients receiving cochlear implants. The purpose of this study was to evaluate preoperative CT studies and compare them to surgical findings in 34 children who received the Nucleus multichannel cochlear implant. The focus of this report is to discuss the dependability of CT scans in predicting surgical findings at the time of cochlear implantation. Results indicate that agreement of CT interpretations with surgical findings is partially related to the etiology of hearing loss and the experience of the surgeon and neuroradiologist. Advantages and limitations of the CT scans in predicting surgical findings are discussed.

Adolescent↗
PubMed1992

Synthesis and phosphorylation of uvomorulin during mouse early development.

The cell adhesion molecule, uvomorulin, is synthesised in both the 135 x 10(3) M(r) precursor and 120 x 10(3) M(r) mature forms on maternal mRNA templates in unfertilized and newly fertilized mouse oocytes. Synthesis on maternal message ceases during the 2-cell stage to resume later on mRNA encoded presumptively by the embryonic genome. Uvomorulin is detectable by immunoblotting at all stages upto the blastocyst stage, but shows variations in its total amount and processing with embryonic stage. Whilst only trace levels of phosphorylated uvomorulin are detectable in early and late 4-cell embryos, uvomorulin in 8-cell embryos is phosphorylated.

Animals↗
PubMed1992

Cell cycle progression of parthenogenetically activated mouse oocytes to interphase is dependent on the level of internal calcium.

Nuclear maturation of the mouse oocyte becomes arrested in metaphase of the second meiotic division (MII). Fertilization or parthenogenetic activation induces meiotic completion, chromosomal decondensation and formation of a pronucleus. This completion of meiosis is probably triggered by a transient increase in cytosolic calcium ions. When activated just after ovulation by a low concentration of the calcium ionophore A23187, the majority of the mouse oocytes go through a metaphase to anaphase transition and extrude their second polar body but they do not proceed into interphase; instead their chromatids remain condensed and a microtubular metaphase spindle reforms (metaphase III). However, a high percentage of these oocytes will undergo a true parthenogenetic activation assessed by the formation of a pronucleus, when exposed to a higher concentration of the calcium ionophore. The capacity of the mouse oocyte to pass into metaphase III is lost with increasing time post-ovulation. Direct measurement of intracellular calcium with Fura-2 reveals higher levels of cytosolic calcium in aged oocytes and/or using higher concentrations of calcium ionophore for activation. It is concluded that the internal free calcium level determines the transition to interphase.

Animals↗
PubMed1992

How does transferrin overcome the in vitro block to development of the mouse preimplantation embryo?

Transferrin promotes development of mouse embryos through the two-cell block in vitro. Uptake of transferrin into blastocysts was shown to occur by both receptor-mediated and nonspecific pathways, but neither pathway was used to a detectable extent by embryos before the eight-cell stage. Conversely, the dialysis of culture medium, non-permissive for development through the two-cell block, against a solution of transferrin rendered it capable of supporting development. It was therefore concluded that transferrin exerts its supportive effect on development in vitro via its chelating effects.

Animals↗
PubMed1992

Effects of glucose, glutamine, ethylenediaminetetraacetic acid and oxygen tension on the concentration of reactive oxygen species and on development of the mouse preimplantation embryo in vitro.

Analysis over the first 48 h of development in vitro from the one-cell stage to the early four-cell stage indicated that (i) ethylenediaminetetraacetic acid (EDTA) exerts the major beneficial effect on culture to the blastocyst stage of F1 and MF1 embryos, (ii) glutamine assists development of MF1, but not F1, embryos to the blastocyst stage and probably functions as part of a metabolic response to oxidative damage to mitochondria and (iii) exposure to glucose at some time during early cleavage is essential for full development to blastocysts. None of the culture conditions examined affected significantly the increase in concentration of reactive oxygen species in late two-cell embryos in vitro, although F1 embryos in vitro often had lower peroxide concentrations than MF1 embryos. A decline in oxygen tension from 20 to 50% had no consistent effect on culture to the blastocyst stage or production of reactive oxygen species. Aminooxyacetate, an inhibitor of transaminase activity, prevented non-blocking embryos from developing beyond G2 of the second cell cycle. It is concluded that the chelation of transitional metals provides the most effective method of overcoming the block to development in vitro.

Animals↗
PubMed1992

Hb Rancho Mirage [beta 143(H21)His----Asp]; a variant in the 2,3-DPG binding site showing normal oxygen affinity at physiological pH.

Hb Rancho Mirage was detected in a 17-year-old male in association with a mild anemia. Hemoglobin electrophoresis revealed the variant had a mobility between Hbs A and J on cellulose acetate (pH 8.6) and a mobility like Hb F on citrate agar (pH 6.4). A substitution of His----Asp was found at position 143 in the beta chain, a residue that contributes to the anionic 2,3-DPG binding site in Hb. This variant exhibited normal oxygen affinity at physiologic pH and reduced affinity at alkaline pH. This suggested a subtle shift in the allosteric equilibrium due most likely to the introduction of a negative charge that stabilized the 2,3-DPG pocket. Both homotrophic (heme-heme) and heterotropic (2,3-DPG and protons) effects were reduced; this might be a consequence of an alteration in the carboxyl terminal region of the beta-subunits. Although a His----Asp substitution would be considered to cause reasonable disruption of the 2,3-DPG and C-terminal conformation of the beta- subunits, the properties of Hb Rancho Mirage suggest that, in fact, there appear to be no major perturbation of the critical C-terminal residues.

2,3-Diphosphoglycerate↗
PubMed1992

Computed tomography of acute cerebral trauma.

Hounsfield's development of computed tomography (CT) in 1972 revolutionized the care of patients with acute craniocerebral trauma. CT evaluation facilitates early surgical and medical intervention and has significantly improved patient outcome. This review describes the role of CT in assessing acute head trauma. Despite the growing role of magnetic resonance imaging in the acute, subacute, and chronic phases of brain injury as well as in many other central nervous system disorders, CT retains its unique capacity to image acutely ill patients rapidly and accurately.

Acute Disease↗
PubMed1991

Congenital cystic eye with multiple ocular and intracranial anomalies.

We describe a newborn with congenital cystic eye, contralateral persistent hyperplastic primary vitreous, and cerebrocutaneous abnormalities. The cerebrocutaneous abnormalities consisted of agenesis of the corpus callosum, midbrain deformity, malformed sphenoid bone, right upper eyelid coloboma, and a left periocular hamartoma. The results of karyotype analysis of the patient and his parents were normal. The association of congenital cystic eye with contralateral persistent hyperplastic primary vitreous has not been previously reported, to our knowledge. Although no unifying diagnosis exists for the collection of anomalies demonstrated in this patient, the term cranial ectodermopathy broadly classifies most of the defects.

Abnormalities, Multiple↗
PubMed1991

Zona pellucida modifications in the mouse in the absence of oocyte activation.

Mouse oocytes arrested in metaphase II exhibit zona hardening and a reduced fertilization rate after exposure to the cryoprotectant dimethylsulfoxide (Johnson J, In Vitro Fertil Embryo Transfer 6:168-175, 1989) but do not undergo parthenogenetic activation (Johnson and Pickering, Development 100:313-324, 1987). This paper shows that dimethylsulfoxide causes proteolytic modification of the zona pellucida glycoprotein ZP2 and inhibition of sperm binding. These effects of dimethylsulfoxide are caused by premature exocytosis of the cortical granules, a process that is initiated usually on fertilization. A model for the mechanism of action of dimethylsulfoxide is proposed based on the combined effects of cytoskeletal modification and osmotic shock. The presence of serum before and during the exposure to dimethylsulfoxide was found to reduce significantly these deleterious effects on the mouse zona pellucida without inhibiting the cortical granule release. These results highlight the suitability of dimethylsulfoxide as a tool to study the mechanisms leading to cortical granule release. Use of dimethylsulfoxide allows the separation of oocyte parthenogenetic activation from cortical granule release, and addition of serum allows separation of cortical granule release from the action of the cortical granule contents. Their use allows a dissection of the mechanisms underlying each of these three related events.

Animals↗
PubMed1991

Newborns' preferential tracking of face-like stimuli and its subsequent decline.

Goren, Sarty, and Wu (1975) claimed that newborn infants will follow a slowly moving schematic face stimulus with their head and eyes further than they will follow scrambled faces or blank stimuli. Despite the far-reaching theoretical importance of this finding, it has remained controversial and been largely ignored. In Experiment 1 we replicate the basic findings of the study. In Experiment 2 we attempt a second replication in a different maternity hospital, and extend the original findings with evidence suggesting that both the particular configuration of features, and some aspects of the features themselves, are important for preferential tracking in the first hour of life. In Experiment 3 we use a different technique to trace the preferential tracking of faces over the first five months of life. The preferential tracking of faces declines during the second month. The possible causes and consequences of this observation are discussed.

Attention↗