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M Tosić

Publications and source records attributed to M Tosić.

3 recordsLinked to original sources
PubMed1998

Myelin basic protein immunoreactivity in the human embryonic CNS.

Myelin basic protein (MBP) is a major myelin constituent produced by oligodendrocytes in the central nervous system (CNS). Expression of MBP was considered to be a marker for oligodendrocyte differentiation and myelination in the developing CNS. In this study, expression of myelin basic protein (MBP) and its messenger RNA (mRNA) was examined in human embryos and fetuses ranging in age from 5 to 20 gestational weeks (g.w.). We were able to demonstrate that MBP antibody labels cells in both human nervous and non-nervous tissues beginning from early embryonic life (5-6 g.w.). MBP positive (MBP+) cells were rounded, with either no cell processes or only 1-2 short processes, and were located in caudal regions of the CNS. MBP+ cells were also observed in the non-nervous tissue, such as leptomeninges, choroid plexus, and connective tissues. A number of MBP+ cells in nervous and non-nervous tissues were morphologically similar to macrophages and showed a positive reaction to macrophage-microglia markers: lectin (RCA-1) and the monoclonal antibody (EBM-11) to human macrophage antigen CD68, whereas they were negative for neuronal, astroglial, or marker for oligodendrocyte progenitors. At the same embryonic age, 5 g.w. and onward, the MBP mRNA was observed in the CNS by in situ hybridization. The results of this study show that MBP immune reaction is spread in a large area of the CNS prior to myelin appearance. In addition, for the first time it has been demonstrated that the same population of cells could be labelled with both MBP and macrophage markers. These results indicate that MBP, or MBP-related proteins, could represent a link between the immune and nervous system during early development. Thus, besides the well established role in myelination, these proteins might have an additional and still unknown function in development.

Central Nervous System↗
PubMedDate not supplied

Density- and frequency-dependent selection at the Mdh-2 locus in Drosophila pseudoobscura.

We have studied differences in the number of Drosophila pseudoobscura produced in a culture when the flies differ with respect to two alleles (F and S) at the Mdh-2 locus, which codes for a malate dehydrogenase enzyme. The studies were done at low and at high density in two- and three-genotype combinations (S/S, F/F and S/F), with one-genotype cultures as controls.--Density affects the fitness of the Mdh-2 genotypes. Different genotypes are differently affected, and the genotype of the competitors also makes a difference on the fitness of a given genotype. When three genotypes are present in a culture, particularly at high density, intergenotypic competition is less intense than intragenotypic competition at several frequency combinations. That is, there is "overcompensation": the three genotypes together exploit the environmental resources better than one genotype alone.--The fitness of the genotypes is frequency dependent in both two-genotype and three-genotype combinations. An inverse relationship between frequency and fitness is observed at high density. This may lead to a stable polymorphism, because the fitness of a genotype increases as its frequency decreases.--Forty independent strains, sampled from a natural population, were used in the experiments. This ensures that more than 95% of the variation present in the genome in the natural population is also present in the experimental cultures. It also ensures that the genetic background on the Mdh-2 alleles is randomized in the same way as it is in nature. However, the possibility remains that Mdh-2 alleles in nature are nonrandomly associated with alleles at closely linked loci. If linkage disequilibrium is present in the experiments because it exists in nature, then the observed effects (such as frequency-dependent selection) would affect the Mdh-2 locus in nature as well.

Alleles↗