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Biomedical subjects

M Dorizzi

Publications and source records attributed to M Dorizzi.

14 recordsLinked to original sources
PubMed1988

Temperature-dependent gonadal differentiation in the turtle Emys orbicularis: concordance between sexual phenotype and serological H-Y antigen expression at threshold temperature.

As in many other turtles, the sexual differentiation of gonads in embryos of Emys orbicularis is temperature-sensitive, 100% phenotypic males being obtained below 27.5 degrees C and 100% phenotypic females above 29.5 degrees C. The expression of the serologically defined H-Y (SD-H-Y) antigen at both low and high temperatures has been shown to be different in gonads and in blood : in gonads, it is closely associated with ovarian structure, whereas in blood it is independent of sexual phenotype and appears to indicate sexual genotype. Both sexes differentiate at 28.5 degrees C, suggesting that at this intermediate (threshold) temperature, sexual differentiation of gonads conforms with sexual genotype. To test this hypothesis, the expression of SD-H-Y antigen has been carried out in blood cells of Emys individuals raised from eggs incubated at the threshold temperature (28.5 degrees C). All phenotypic males typed SD-H-Y negative, whereas most phenotypic females typed SD-H-Y positive. From this concordance between sexual phenotype of gonads and SD-H-Y phenotype of blood, we postulate that a ZZ male/ZW female mechanism of genotypic sex determination is revealed at the threshold temperature for gonad differentiation in Emys.

Animals↗
PubMed1984

A memory effect in DNA replication.

A study of the polymerization/excision ratio in the replication of poly(dA), primed with oligo(dT), was carried out with E. coli DNA polymerase I, at various primer and enzyme concentrations. The variations in this ratio suggest that 1) the DNA polymerase is able to switch between two states of low and high exonuclease activities and 2) after dissociating from the template, the DNA polymerase drifts towards the low exonuclease state. The recovery of the high exonuclease state would require several successive incorporations.

DNA Polymerase I↗
PubMed1982

H-Y antigen expression in temperature sex-reversed turtles (Emys orbicularis).

H-Y antigen has been used as a marker for the heterogametic sex and is assumed to be an organizing factor for the heterogametic gonad. In the turtle Emys orbicularis, H-Y antigen is restricted to the female cells, indicating a female heterogamety (ZZ/ZW) sex-determining mechanism. Moreover, the sexual differentiation of the gonads is temperature sensitive, and complete sex reversal can be obtained at will. In this framework the relationships between H-Y antigen, temperature, and gonadal phenotype were studied. Mouse H-Y antiserum was absorbed with blood and gonadal cells of control wild male and female adults, and with blood and gonadal cells from three lots of young turtles from eggs incubated at 25-26 degrees C (100% phenotypic males), at 30-30.5 degrees C (100% phenotypic females), or at 28.5-29 degrees C (majority of females with some males and intersexes). The residual activity of H-Y antiserum was then estimated using an immunobacterial rosette technique. In adults, both blood cells and gonadal cells were typed as H-Y negative in males and as H-Y positive in females. In each of the three lots of young, blood cells were H-Y negative in some individuals and H-Y positive in others. The proposed interpretation is that the H-Y negative individuals were genotypic males (ZZ) and the H-Y positive were genotypic females (ZW). The gonads of these animals were then pooled in different sets according to their sexual phenotype and to the presumed genotypic sex (i.e., blood H-Y phenotype). Testicular cells were typed as H-Y negative in genotypic males as well as in the presumed sex-reversed genotypic females; likewise, ovarian cells were typed as H-Y positive in genotypic females as well as in the presumed sex-reversed genotypic males. These results provide additional evidence that H-Y antigen expression is closely associated with ovarian structure in vertebrates displaying a ZZ/ZW sex-determining mechanism.

Animals↗
PubMed1982

Polymerization/excision kinetics of Escherichia coli DNA polymerase I. Stability in kinetic behaviour and variations of the rate constants with temperature and pH.

1. The incorporation and excision kinetics of Escherichia coli DNA polymerase I in the replication of (dA)n with dUTP and (dI)n with dCTP was studied at various temperatures and pH. When the incorporation/excision ratio (dy/dx) is plotted against the concentration of deoxynucleoside triphosphate [S] two kinds of curves are obtained. With (dI)n, dy/dx increases with [S], then reaches an asymptotic value. This behaviour, consistent with a kinetic amplification or kinetic proofreading mechanism, is observed at all temperatures and pH. With (dA)n, dy/dx increases with [S] but in a convex, instead of a concave manner. In this case, we approximated the curves by straight lines at the origin, in conformity with the prediction of the frayed-unfrayed model. Again a single behaviour is consistently observed at all temperatures and pH. 2. The data were analyzed in terms of ratios or products of three kinetic constants: ki for incorporation, ke for excision and, in the (dI)n system, theta for the processing of the incoming dNTP. The dNMP production in the (dI)n system is dominated by the ke theta term which increases with temperature and pH. Temperature influences excision more than incorporation, the net result being a linear decrease of ki/ke with temperature. The effect is more pronounced with (dI)n than with (dA)n and is probably related to the stability of the template-primer complex. The ki/ke term shows a bell-shaped dependency with pH in the (dI)n system. With (dA)n it remains constant between pH 7.5 and 8.5 then decreases with a transition midpoint at pH 9.0. We suggest that the pH profiles may reflect the ionization of the template in the first case, and of the substrate in the second.

Bacterial Proteins↗
PubMed1977

Aminoacylation of tRNA Trp from beef liver, yeast and E. coli by beef pancrease tryptophan-tRNA ligase. Stoichiometry of tRNATrp binding.

The Michaelis constants and the maximum velocities in the aminoacylation reaction of tRNATrp from beef liver, yeast and E. coli by pure beef pancreas tryptophan-tRNA ligase show that this mammalian enzyme recognizes and charges the two eucaryotic tRNAs with the same efficiency. The rate of aminoacylation of the procaryotic tRNATrp by the enzyme is three orders of magnitude lower. The pH optimum of aminoacylation is 8 for both eucaryotic tRNAs. The optimum magnesium concentration is different. The rate is maximum when magnesium concentration is stoichiometric to ATP concentration for tRNATrp from beef liver and 10 mM above ATP concentration for tRNATrp from yeast. The number of binding sites on the enzyme for the two eucaryotic tRNAs has been measured by equilibrium filtration on Sephadex G-100 and found equal to two.

Adenosine Triphosphate↗
PubMed1976

Purification of tRNATrp, tRNAVal, and partial purification of tRNAIle and tRNAMfet from beef liver.

tRNATrp from beef lever has been purified by classical chromatographical methods. Total tRNA, prepared on a large scale (total aminoacid acceptance 1280 pmol/A260 unit) was submitted to chromatography on benzoylated-DEAE cellulose, then DEAE Sephadex. The major species accepting tryptophan issued from the second chromatography was aminoacylated with [14C] tryptophan and chromatographed on benzoylated-DEAE cellulose. The tRNA carrying the radioactive label was eluted in the ethanolic region. After stripping, the resulting tRNATrp has an acceptance of 1800 pmol/A260 unit. No isoacceptors could be demonstrated by chromatography of the pure species on RCP 5 in 6 M urea. The yield in pure tRNATrp was currently in the range of 25 to 30 percent of the total tryptophan acceptance of the starting curde tRNA.

Amino Acids↗
PubMed1975

Increase in the proportion of cells with the C'3 receptor in BALB/c mice bearing mammary tumors.

Transplantation of mammary tumors originally induced by dimethylbenzanthracene caused splenomegaly and an increase in the total population of spleen cells paralleling the increase in tumor size. At least part of the hypercellularity was due to in situ proliferation as evidenced by the increased number of blast forms and mitotic figures. The cells were characterized with respect to parameters generally associated with B-cells; surface immunoglobulins as detected by immunofluorescence and C'3 receptors as determined by rosette formation with sheep red blood cells (SRBC) coated with rabbit anti-SRBC and mouse complement. There was no change in the percentage of B-cells with surface immunoglobulin in tumor-bearing mice compared with the control animals. However, there was a profound change in the representation of cells bearing C'3 receptors. The percentage of the cells increased dramatically with tumor growth. Various possibilities regarding the nature and function of these cells are considered.

Animals↗