[Genetic analysis of the hybridization zone between two subspecies Mus musculus domesticus and Mus musculus musculus in Bulgaria]. / Analyse génétique de la zone d'hybridation entre les deux sous-espèces de souris Mus musculus domesticus et Mus musculus musculus en Bulgarie.

The hybrid zone between the two subspecies of mice Mus musculus domesticus and Mus musculus musculus, which has been studied extensively in Denmark, crosses Europe to the Black Sea through the Alps and the Balkans. Two hundred and seventy-nine animals were captured in 22 localities along a transect across the Balkans. The animals were characterized for seven diagnostic nuclear loci by protein electrophoresis and by restriction pattern analysis of their mitochondrial DNA. The nuclear data show a sharp transition between the two subspecies, most of the variations in allele frequencies (from 0.9 to 0.1) occurring within a 36-km section of the transect. The introgression varies from one locus to the other and is more pronounced, in terms of distance, in M. m. musculus territory. Mitochondrial DNA introgression is important but occurs in one direction only, i.e. from M. m. musculus to M. m. domesticus, while a cytoplasmic transfer from M. m. domesticus to M. m. musculus has been reported. A previous study showed that no Y chromosome introgression occurs. The different behaviour of these three types of markers could be due to the interaction between selection against hybrid genomes and meiotic recombination. Objectively, it would appear that the genes that can introgress are neutral or nearly so and have been separated from deleterious genes they were linked to by recombination. This could explain the differential introgression between autosomal loci. The mitochondrial and Y chromosomes undergo no or very little recombination and each is transmitted as a whole. Their degree of introgression is thus indicative of the intensity of selection resulting from the amount of functional differentiation between the two taxa, which seems to be strong for the Y chromosome and weak for mitochondrial DNA. We propose that the asymmetry of nuclear introgression is due to different population structures. As M. m. musculus is relatively less structured, the rapid spreading of introgressed genes would be favoured. Such a scheme, however, can hardly account for the unidirectionality of the mitochondrial flow, which could be due to sex-dependent behaviour.

The effect of liposome-entrapped specific cell growth inhibitor (chalone) on tumour cell proliferation.

The effect of specific cell growth inhibitor (chalone) on the mitotic activity of ascites ISM applied entrapped in liposomes compared to the non-entrapped 'free' form was investigated. The 'free' chalone injected intraperitoneally in BALB/c ascites ISM-bearing mice (1500 mg per kg body weight) decreased the mitotic activity of the tumour by 66 per cent 2.5 h after administration. Five hours after administration, complete restoration of the mitotic index to the control level was observed. Chalone encapsulated into Bangham liposomes (1000 mg per kg body weight) in otherwise identical conditions produced 44 per cent inhibition after 2.5 h, while at 5 h post-injection the mitotic inhibition was still present increasing up to as much as 50 per cent. No such effect was evident by chalone encapsulated in freeze-thawed liposomes (500 mg per kg body weight). The chalone under study specifically inhibits the cell division of the originating tumour cells and has no effect on its DNA synthesis or on the mitosis of the basal layer of the oesophagus and crypts of the intestinal epithelium. The results obtained provide evidence that liposome-entrapped chalone prolongs the inhibition of tumour cell mitosis in comparison to the 'free' one even in a reduced dose. Some possible applications of this approach concerning cancer research and treatment are discussed.

Isolation and partial characterization of IgM-like immunoglobulins from the serum of carp (Cyprinus carpio L.), frog (Rana ridibunda Pall.) and tortoise (Testudo graeca Pall.).

1. IgM-like immunoglobulin fractions have been isolated by combinations of precipitation procedures and gel-filtration from the serum of three vertebrate species, representative of the classes of Pisces (Cyprinus carpio L.), Amphibia (Rana ridibunda Pall.) and Reptilia (Testudo graeca Pall.). 2. The homogeneity of the isolated fractions has been confirmed electrophoretically and immunoelectrophoretically. 3. Electrophoretic mobility of IgM, similar for the three species studied has been observed in polyacrylamide gel; in agar gel immunoelectrophoresis carp and frog IgM mobilities are almost identical, in contrast to the markedly slower cathodic migration of tortoise IgM.

[Role of adhesive lymphoid cell subpopulation in areactivity to hepatoma 22a]. / Izuchenie roli prilipaiushchei subpopuliatsii limfoidnykh kletok v areaktivnosti k gepatome 22a.

The role of adhesive fraction of T lymphocytes in nonreactivity of mice to hepatoma 22a was studied. It was shown that the removal of the adhesive fraction from the spleen suspension enriched with T lymphocytes promotes intensification of cell immunity in tumor-tolerant mice.

[Detection of stage specific and organ specific human brain antigens during embryogenesis]. / Obnaruzhenie stadiospetsificheskikh i organospetsificheskikh antigenov mozga cheloveka v émbriogeneze.

The rabbit antisera were obtained against the water soluble antigens of the brain of 8--10 weeks old human foetuses. Three groups of specific antigens were identified in the brain of human foetuses: 1) antigens common for the embryonic brain and other organs of the same age; 2) antigens common for the embryonic brain and some organs of the adult organism; 3) stage (phase)-specific brain antigens present only in the brain between the 8th and 10th weeks of pregnancy.