Biomedical subjects

A P Alves

Publications and source records attributed to A P Alves.

6 recordsLinked to original sources

PubMed2006

Inheritance of resistance to the Cry1Ab Bacillus thuringiensis toxin in Ostrinia nubilalis (Lepidoptera: Crambidae).

Laboratory selection with Cry1Ab, the predominant Bacillus thuringiensis (Bt) toxin in transgenic corn, Zea mays L., produced >1000-fold resistance in two laboratory strains of European corn borer, Ostrinia nubilalis (Hübner). We tested the offspring of various crosses to determine the mode of inheritance of resistance to Cry1Ab. Patterns of inheritance of resistance were similar in the two resistant strains. The progeny of reciprocal F1 crosses (resistant male x susceptible female and vice versa) responded alike in bioassays, indicating autosomal inheritance. The median lethal concentrations (LC50 values) of F1 were intermediate between the resistant and susceptible parents, indicating approximately additive inheritance. However, the dominance of resistance increased as the concentration of Cry1Ab decreased. Analysis of progeny from backcrosses (F1 x susceptible strain) suggests that resistance was controlled by more than one locus. In particular, the fit of observed to expected mortality improved as the number of putative loci increased from 1 to 10. The polygenic nature of resistance in these two laboratory strains suggests that major genes for resistance to Cry1Ab were not common in the founding populations of O. nubilalis. A low initial frequency of major genes for Cry1Ab resistance might be an important factor in delaying evolution of resistance to Bt corn in this pest.

Animals↗

PubMed1999

Structure of the sulfated alpha-L-fucan from the egg jelly coat of the sea urchin Strongylocentrotus franciscanus: patterns of preferential 2-O- and 4-O-sulfation determine sperm cell recognition.

The egg jelly coats of sea urchins contains sulfated polysaccharides responsible for inducing the sperm acrosome reaction which is an obligatory event for sperm binding to, and fusion with, the egg. Here, we extend our study to the sea urchin Strongylocentrotus franciscanus. The egg jelly of this species contains a homofucan composed of 2- O -sulfated, 3-linked units which is the simplest structure ever reported for a sulfated fucan. This polysaccharide was compared with other sulfated alpha-L-fucans as inducers of acrosome reaction in conspecific and heterospecific sperm. Although all these fucans are linear polymers composed of 3-linked alpha-L-fucopyranosyl units, they differ in the proportions of 2-O- and 4-O-sulfation. The reactivity of the sperm of each species is more sensitive to the egg jelly sulfated fucan found in their own species. The reactivity of the sperm does not correlate with the charge density of the fucan, but with the proportion of 2-O- and 4-O-sulfation. The pattern of sulfation may be an important feature for recognition of fucans by the sperm receptor contributing to the species-specificity of fertilization.

Acrosome Reaction↗

PubMed1998

Females of the sea urchin Strongylocentrotus purpuratus differ in the structures of their egg jelly sulfated fucans.

The egg jelly coats of sea urchins contain sulfated fucans which bind to a sperm surface receptor glycoprotein to initiate the signal transduction events resulting in the sperm acrosome reaction. The acrosome reaction is an ion channel regulated exocytosis which is an obligatory event for sperm binding to, and fusion with, the egg. Approximately 90% of individual females of the sea urchin Strongylocentrotus purpuratus spawned eggs having only one of two possible sulfated fucan electrophoretic isotypes, a slow migrating (sulfated fucan I), or a fast migrating (sulfated fucan II) isotype. The remaining 10% of females spawned eggs having both sulfated fucan isotypes. The two sulfated fucan isotypes were purified from egg jelly coats and their structures determined by NMR spectroscopy and methylation analysis. Both sulfated fucans are linear polysaccharides composed of 1-->3-linked alpha-L-fucopyranosyl units. Sulfated fucan I is entirely sulfated at the O -2 position but with a heterogeneous sulfation pattern at O -4 position. Sulfated fucan II is composed of a regular repeating sequence of 3 residues, as follows: [3-alpha-L-Fuc p -2,4(OSO3)-1-->3-alpha-L-Fuc p -4(OSO3)-1-->3-alpha-L-Fuc p -4(OSO3)-1]n. Both purified sulfated fucans have approximately equal potency in inducing the sperm acrosome reaction. The significance of two structurally different sulfated fucans in the egg jelly coat of this species could relate to the finding that the sperm receptor protein which binds sulfated fucan contains two carbohydrate recognition modules of the C-type lectin variety which differ by 50% in their primary structure.

Acrosome↗

PubMed1997

Sulfated polysaccharides from the egg jelly layer are species-specific inducers of acrosomal reaction in sperms of sea urchins.

We have characterized the fine structure of sulfated polysaccharides from the egg jelly layer of three species of sea urchins and tested the ability of these purified polysaccharides to induce the acrosome reaction in spermatozoa. The sea urchin Echinometra lucunter contains a homopolymer of 2-sulfated, 3-linked alpha-L-galactan. The species Arbacia lixula and Lytechinus variegatus contain linear sulfated alpha-L-fucans with regular tetrasaccharide repeating units. Each of these sulfated polysaccharides induces the acrosome reaction in conspecific but not in heterospecific spermatozoa. These results demonstrate that species specificity of fertilization in sea urchins depends in part on the fine structure of egg jelly sulfated polysaccharide.

Acrosome↗

PubMed1994

Sulfated fucans from echinoderms have a regular tetrasaccharide repeating unit defined by specific patterns of sulfation at the 0-2 and 0-4 positions.

Sulfated fucans from echinoderms (sea cucumber and sea urchin) have a linear backbone of 1-->3-linked alpha-L-fucopyranose with some sulfate substitution at the 2- and 4-positions. NMR spectroscopy indicates that both polysaccharides have a tetrasaccharide repeat unit in which the separate residues differ only in the extent and position of their sulfate substitution. The sea urchin fucan has the structure, [formula: see text] This type of regular structure has not previously been described, and is in contrast with the random arrangement of substituents on the similar 1-->3-linked alpha-L-fucopyranose backbone of the fucoidans from brown algae.

Animals↗

PubMed1993

Known heat-shock proteins are not responsible for stress-induced rapid degradation of ribosomal protein mRNAs in yeast.

We have previously shown that the heat-induced enhanced decay of yeast mRNAs encoding ribosomal proteins (rp-mRNAs) requires ongoing transcription during the heat treatment [Herruer et al. (1988) Nucl. Acids Res. 16, 7917]. In order to determine whether this requirement reflects the need for heat-shock protein (hsp), we analysed the effect of heat shock on rp-mRNA levels in several yeast strains in which each of the heat-shock genes encoding hsp26, hsp35 or hsp83 had been individually disrupted. In all three strains we still observed increased degradation of rp-mRNAs immediately after the temperature shift, demonstrating that hsp26, hsp35 and hsp83 are not required for this effect. Accelerated turnover of rp-mRNA was also found to occur upon raising the growth temperature of a mutant strain that contains a disruption of the gene specifying the heat-shock transcription factor and in wild-type yeast cells treated with canavanine, an arginine analogue that will be incorporated into all known hsps and that is known to cause misfolding of the polypeptide chain. Latter observation suggests that enhanced rp-mRNA decay is a more general stress-related phenomenon. Taken together, these data strongly indicate that the trans-acting factor required for the increase in the rate of degradation of rp-mRNAs upon stress is not one of the known yeast hsps.

Canavanine↗