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S L Varmuza

Publications and source records attributed to S L Varmuza.

10 recordsLinked to original sources
PubMed2001

Xenopus adenine nucleotide translocase mRNA exhibits specific and dynamic patterns of expression during development.

We report the isolation and characterization of the Xenopus homolog to human T1 ANT (adenine nucleotide translocase). The 1290-nucleotide sequence contains initiation and termination signals, and encodes a conceptual protein of 298 amino acids. The sequence shares high amino acid identity with the mammalian adenine translocases. The transcript is present in unfertilized eggs, and it is expressed at higher levels during formation of the antero-posterior dorsal axis in embryos. Although low levels are expressed constitutively except in endodermal cells, adenine nucleotide translocase (ANT) expression is dynamically regulated during neurulation. At this stage, expression in ectoderm rapidly diminishes as the neural folds form, and then ANT expression increases slightly in mesoderm. At the culmination of neurulation, the neural tube briefly expresses ANT, and thereafter its expression predominates in the somitic mesoderm and also the chordoneural hinge. In addition, ANT expression is particularly high in the prosencephalon, the mesencephalon, the branchial arches, eye, and the otic vesicle. Treatment of embryos with retinoic acid has the effect of diminishing constitutive expression of ANT, but microinjection studies demonstrate that immediate and local repression cannot be induced in dorsal structures.

Amino Acid Sequence↗
PubMed1998

Expression and regulation of genes associated with cell death during murine preimplantation embryo development.

The newly fertilized preimplantation embryo depends entirely on maternal mRNAs and proteins deposited and stored in the oocyte prior to its ovulation. If the oocyte is not sufficiently equipped with maternally stored products, or if zygotic gene expression does not commence at the correct time, the embryo will die. One of the major abnormalities observed during early development is cellular fragmentation. We showed previously that cellular fragmentation in human embryos can be attributed to programmed cell death (PCD). Here, we demonstrate that the PCD that occurs during the 1-cell stage of mouse embryogenesis is likely to be regulated by many cell death genes either maternally inherited or transcribed from the embryonic genome. We have demonstrated for the first time the temporal expression patterns of nine cell death regulatory genes, and our preliminary experiments show that the expression of these genes is altered in embryos undergoing fragmentation. The expression of genes involved in cell death (MA-3, p53, Bad, and Bcl-xS) seems to be elevated, whereas the expression of genes involved in cell survival (Bcl-2) is reduced. We propose that PCD may occur by default in embryos that fail to execute essential developmental events during the first cell cycle.

Animals↗
PubMed1995

Two isoforms of Xenopus retinoic acid receptor gamma 2 (B) exhibit differential expression and sensitivity to retinoic acid during embryogenesis.

We report the isolation of two retinoic acid receptor isoforms (RAR gamma), which differ only in the 5'untranslated and putative N-terminus A regions. The two isoforms appear to serve as early markers for the presumptive neural axis; however, their expression patterns differ. RAR-gamma 2.1 is first expressed at gastrulation at the dorsal lip and subsequently along the presumptive neural axis. RAR- gamma 2.2 represents the full-length sequence of a receptor cDNA already partially characterized and present as a maternal transcript [Ellinger-Ziegelbauer and Dreyer (1991); Genes Dev 5:94-104, (1993): Mech Dev 41:31-46; Pfeffer and DeRobertis, (1994) Mech Dev: 45:147-153]. Unlike RAR-gamma 2.2, the 2.1 variant is not expressed either in pre-somitic mesoderm or notochord. RAR-gamma 2.1 is strongly expressed in branchial arches and to a lesser extent in the neural floor plate. The two isoforms also exhibit differential sensitivity to retinoic acid. Constitutive expression of RAR gamma 2.2 following neurulation appears to be depressed by treatment with retinoic acid, but domains of highest expression, namely, the head and tail, remain relatively unaffected, as do patterns of expression prior to late neurulation. By contrast, RAR-gamma 2.1 is not transcribed in retinoid-inhibited structures. Using microinjection techniques, we show that changes of RAR-gamma 2.1 expression in presumptive head structures occur as an early and local consequence of retinoic acid administration. Since RAR-gamma 2.1 expression is inhibited by retinoic acid, we tested to see if other treatments that perturb axis formation had any effect. Surprisingly, UV irradiation did not suppress that its inhibition by retinoic acid is not due solely to inhibition of anterior neural development. These experiments demonstrate a new subdivision of isoforms that undergo differential expression during development and that exhibit differential sensitivity to retinoic acid and to UV. This sensitivity and the presence of this isoform variant in regions that are known to exhibit polarizing activity strengthen the hypothesis that these receptors play a primary role during morphogenesis.

Amino Acid Sequence↗
PubMed1995

Recombinant human leukemia inhibitory factor does not enhance in vitro human blastocyst formation.

OBJECTIVE: To assess the effect of human recombinant leukemia inhibitory factor in different doses on human blastocyst formation. SETTING: A university-based tertiary referral center (The Toronto Hospital). INTERVENTIONS: Nontransferable human embryos (n = 473) at the two- to six-cell stage were obtained from patients undergoing IVF and were split randomly into five groups. Embryos in group A (n = 164) were cultured as the control group in Ham's F-10 (GIBCO-BRL, Grand Island, NY) + 10% human sera. Embryos in groups B, C, D, and E (n = 54, 78, 87, and 80, respectively) were cultured in the same medium supplemented with human recombinant leukemia inhibitory factor in four different concentrations (5, 7.5, 10, and 20 ng/mL, respectively). Morphological assessment of embryo development was recorded daily. MAIN OUTCOME MEASURE: Human blastocyst formation. RESULTS: No significant difference was detected in the rate of blastocyst formation of embryos in the study groups when compared with embryos in group A. CONCLUSIONS: This study shows that 5 to 20 ng/mL of recombinant leukemia inhibitory factor in standard medium does not enhance in vitro human blastocyst formation. It is possible that recombinant leukemia inhibitory factor may play a role at later stages of human embryogenesis and during implantation.

Blastocyst↗
PubMed1985

Signals for site-specific cleavage of HSV DNA: maturation involves two separate cleavage events at sites distal to the recognition sequences.

Mature Herpes Simplex Virus (HSV) genomes are cleaved from concatemeric precursors by a site-specific mechanism. These cleavage events are probably coupled to the encapsidation process. Sequences within the terminal repeat of HSV DNA are necessary for the cleavage and packaging reactions, and are also thought to be responsible for high frequency genome isomerization events. Here we present evidence to show that two viral DNA cleavage and packaging signals reside within a 250 bp subfragment of the terminal repeat, that the termini of mature viral DNA are generated by a process involving two separate DNA cleavages at sites distal to the cleavage signals, and that the sequences between these two cleavage sites are duplicated by the DNA maturation system.

Base Sequence↗
PubMed1984

Unstable heterozygosity in a diploid region of herpes simplex virus DNA.

We have examined the behavior of a herpes simplex virus strain KOS isolate in which the two inverted repeats flanking the short segment of viral DNA differ in length by approximately 60 base pairs. We find that individual viral DNA molecules exist which contain the two distinguishable repeats, demonstrating that heterology between the repeats is tolerated. However, viruses heterozygous for the two different repeats are unstable, segregating both classes of homozygotes at a high frequency. We propose that this segregation is a consequence of the high-frequency recombination events which also result in genome segment inversion.

Animals↗
PubMed1980

Supersensitivity in rat caudate nucleus: effects of 6-hydroxydopamine on the time course of dopamine receptor and cyclic AMP changes.

The intranigral administration of 6-hydroxydopamine resulted in the destruction of dopaminergic nerve terminals in the rat caudate nucleus and a 98% decrease in dopamine content. The time courses of the effects of this treatment on dopamine stimulated cyclic 3',5'-AMP accumulation in slices of caudate nucleus and on dopamine receptors in two behaviorally distinct denervation syndromes were determined in an investigation of the mechanisms underlying supersensitivity in this system. The density of dopamine receptors was determined by measuring the high affinity binding of the dopamine receptor antagonist [3H]haloperidol. The density of dopamine receptors was decreased 4 days after the lesion surgery and this effect was probably due to the loss of presynaptic receptors. The density of dopamine receptors and the acumulation of cyclic AMP then increased, with a slower time course, reaching peak levels 10 days after lesioning. The maximal increase in density of dopamine receptors was 70% in both denervation syndromes, while the maximal increase in dopamine-stimulating cyclic 3',5'-AMP levels was 300% at maximally stimulating concentration. The equilibrium dissociation constant (Kd) for haloperidol remained unchanged for 3 weeks following denervation, but there was a slight increase in Kd 40 days post-surgery. The turning behaviour in both syndromes was correlated with a decrease in doapmine levels. The present results are consistent with the notion that the supersensitivity to dopamine that occurs in caudate nucleus following 6-hydroxydopamine lesions has both pre- and post-synaptic components in both syndromes.

Animals↗
PubMed1978

Phenylalanyl synthetase function in cultured fibroblasts from subjects with progeria.

Since progeria cells contain a diversity of altered proteins, some aspects of phenylalanyl synthetase function were examined in semipurified extracts of cultured skin fibroblasts using mixed rabbit tRNA as acceptor. No significant differences were found in the Km and Vmax for phenylalanine or ATP in progeria cells compared with controls. Initial velocities of both progeria and control synthetases were lower at late passage owing to either reduced enzyme content or reduced catalytic efficiency. Reverse phase 5 chromatography of tRNAs acylated by progeria and control synthetases gave a single peak of labeled phenylalanine tRNA in all cases with no secondary peaks evident. Total activity of phenylalanyl synthetase in progeria cells was similar to that of control cells at early passage while late-passage control cells had lower specific activities of these synthetases per unit protein.

Adenosine Triphosphate↗