Mitochondrial DNA and bindin gene sequence evolution among allopatric species of the sea urchin genus Arbacia

Sea urchins of the genus Arbacia (order Stirodonta) have discontinuous allopatric distributions ranging over thousands of kilometers. Mitochondrial DNA (mtDNA) sequences were used to reconstruct phylogenetic relationships of four Arbacia species and their geographic populations. There is little evidence of genetic structuring of populations within species, except in two cases at range extremes. The mtDNA sequence differentiation between species suggests that divergence occurred about 4-9 MYA. Gene sequences encoding the sperm protein bindin and its intron were obtained and compared with the mtDNA phylogeny. Sea urchins among the well-studied echinoid order Camarodonta, with degrees of mtDNA divergence similar to those of Arbacia species, are known to have remarkable variation in bindin. However, in Arbacia, little variation in deduced amino acid sequences of bindin was found, indicating that purifying selection acts on the protein. In contrast, bindin intron sequences showed much differentiation, including numerous insertion/deletions. Fertilization experiments performed between a divergent pair of Arbacia species from the Atlantic and Pacific Oceans revealed no evidence of blocks to gamete recognition. In Arbacia, fertilization specificities may have evolved relatively slowly as a result of extensive gene flow within species, greater functional constraint on the bindin polypeptide, or reduced selective pressure for species recognition in singly occurring species.      

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.      

Antioxidant defense and trace element imbalance in patients with postradiation syndrome

More than 6000 residents of Latvia were involved in recovery work in Chernobyl. They were healthy men exposed to substantial ionizing radiation (0.01–0.5 Gy). Now, these recovery workers suffer from “postradiation syndrome”: dizziness and poor memory, headache, local pains, and so forth. The biochemical mechanism of “postradiation syndrome” has not been completely established. In this Phase I study, we have investigated how exposure to radiation impacts antioxidative defense and trace element concentrations in the blood of recovery workers. Thirty-five patients with postradiation syndrome (men, age range 33–50 yr) and 15 healthy men similar in age as control subjects were studied for the effects on plasma chemiluminescence, the activity of antioxidant enzymes, and the concentration of ceruloplasmin and concentrations of selenium (Se), zinc (Zn), and copper (Cu) in blood. The results revealed that plasma chemiluminescence was significantly increased (3.5-fold to 5.5-fold), the activity of catalase in erythrocytes was significantly elevated, and the activity of glutathione peroxidase in plasma was significantly reduced in examined patients. Concentrations of Zn and Cu were significantly higher and the concentration of Se was lower in these patients. We conclude that the patients exposed to ionizing radiation have diminished blood antioxidant defense associated with pronounced Se deficiency and imbalance of Zn and Cu. Presented in part on the SFRR (Europe) Summer Meeting in Dresden, July 2–5, 1999.     

The interaction between nerve cells and carbon nanotube networks made by CVD process investigation

In this research we investigate neuroblastoma cells cultivated on single-walled carbon nanotubes networks made by CVD method on silicon substrates. The complex analysis of grown cells made by atomic force, electron microscopy and Raman spectroscopy was carried out and the effect of nanotube growth process on proliferation factor was investigated. It is shown that despite of a weak decrease in proliferation, cell morphology remains unchanged and no physical or chemical interaction between carbon nanotubes and cells is observed. The results of the research can be used to investigate the interaction between conductive nano- materials and cells for the development of neural replacement implants. Also they can be useful in bio-electronic interface investigation of signal propagation in neurons.     

Model of active transport of ions in biomembranes based on ATP-dependent change of height of diffusion barriers to ions

A closed model of the active transport was constructed taking into account ATP-dependent opening and closing of barriers to ions and the relationship between the membrane potential and the work of ionic pumps under the condition of electroneutrality inside the cell. The internal consistency of the model was verified by the fulfillment of Onsager's reciprocity relation. It was demonstrated that at the limit of large energy barriers the operation of the system of the active transport is equivalent to the "turning segment" model, which was proposed by the authors earlier. Values of the resting potential and the intracellular concentration of ions were obtained for different types of cells. These results were in qualitative agreement with relevant experimental data.     

A factor which modifies the interaction of steroids with glucocorticoid receptors

A mechanism which determines the difference in the ability of deoxycorticosterone (DOC) to inhibit the binding of 3H-triamcinolone acetonide (3H-TA) to glucocorticoid receptors of rat heart and liver cytosols was investigated. DOC was found to strongly inhibit the binding of 3H-TA by heart cytosol, but to exert only a slight inhibitory effect towards the live cytosol binding. This difference was not due to the influence of the enzymes sensitive to molybdate ions, the presence of DOC-degrading enzymes or contamination of liver cytosol by blood serum. The liver cytosol devoid of the glucocorticoid receptor activity by heating was found to contain a factor modifying the "in vitro" interaction of DOC with the heart cytosol glucocorticoid receptors (receptor modifying factor, RMF). This factor is coeluted with the high molecular weight fraction during gel filtration, is precipitated at 50-70% ammonium sulphate saturation, can be absorbed by DEAE-Sephacel from cytosol at pH 7.4 under hypotonic conditions and extracted at about 0.06 M KC1. The sensitivity to proteases and the lack of sensitivity to nucleases point to the proteinic nature of the factor. It was assumed that in terms of the interaction of some steroids with glucocorticoid receptors, the tissue specificity can, at least partly, be explained by the differences in RMF concentration.