[Transposition of the bobbed locus in Drosophila melanogaster]. / Transpozitsii lokusa bobbed u Drosophila melanogaster.

Due to the complete absence of ribosomal DNA (genetic symbol bb-), the Xbb- chromosome of Drosophila is lethal both in homozygous conditions and in compound with the Xbb- chromosome. However, in the cross between the C(1)RM/Ybb- females and the Xbb-/BSYbb+ males, characterized by the development of lethal Xbb-/Ybb- zygotes, two fertile males were detected. These males possessed all the markers of the Xbb- chromosome but lacked the Y chromosome BS marker. Genetic analysis of their progeny showed that genes responsible for restoration of viability and fertility of these exceptional males were associated with the X chromosome. The crossover tests showed that in one case these genes were tightly linked to the w locus (the bbAM1 allele), and in the second case they were located 12.6 map units to the right of the Tu locus (the bbAM7 allele). It has also been shown that the bb locus was transposed to the X chromosome within the short arm of Y chromosome. Transposition of the BSYbb+ chromosome-specific rDNA sequences to the X chromosome was confirmed by means of Southern blotting. These data indicate that replacement of the bb locus is realized by transposition rather than recombination.

Morphogenesis of rat cranial meninges. A light- and electron-microscopic study.

The meninges of albino Wistar rat embryos, aged between the 11th embryonic day (ED) and birth, were sectioned using a specially constructed device. This technique permits optimal microanatomical preservation of all tissues covering the convexity of the brain: skin, muscle, cartilage or bone, and the meninges. At ED11, the zone situated between the epidermis and the brain is occupied by a mesenchymal network. At ED12, part of this delicate network develops as a dense outer cellular layer, while the remainder retains its reticular appearance, thus forming an inner layer (the future meningeal tissue). At ED13, the dura mater starts to differentiate. At ED14, the bony anlage of the skull can be identified, and along with the proceeding maturation of dura mater some fibrillar structures resembling skeletal muscle fibers appear in the developing arachnoid space. At ED15-17, a primitive interface zone - dura mater/arachnoid - is formed, comprised by an outer electronlucent and an inner electron-dense layer marking the outer aspect of the arachnoidal space. At ED18-19, the innermost cellular row of the inner dural layer transforms into neurothelium, which is separated from the darker arachnoidal cells by an electron-dense band. The arachnoidal trabecular zone with the leptomeningeal cells is formed at ED19. By the end of the prenatal period (ED20-21), its innermost part organizes into an inner arachnoidal layer and an outer and inner pial layer. The results from this study indicate (i) that dura mater and leptomeninges develop from an embryonic network of connective tissue-forming cells, and (ii) that the formation of cerebrospinal fluid (CSF)-containing spaces accompanies the differentiation of the meningeal cellular layers.

Ultrastructural localization of the membrane-bound Mg-adenosine triphosphatase activity in rat meninges.

The distribution of the membrane-bound magnesium ions-dependent adenosine triphosphatase (Mg-ATPase) activity has been studied ultracytochemically in rat meninges by the method of Wachstein and Meisel (1957). A device specially constructed to avoid preparation artefacts has been used to obtain sections from the parietal region of the head. The meninges display an intense though irregularly distributed ATPase activity marked by depositions of electron-dense reaction product (RP) which is almost absent in the outer and middle dural layers. In the borderline zone between dura mater and the arachnoid the RP deposits are found at the outer surface of the inner dural cells and at the contact sites between these cells and the dural neurothelium. The intercellular cleft(s) between the neurothelium and the outer arachnoidal layer, occupied by an "electron-dense band", remains free of RP. The strongest accumulations of reactions granules are observed on the surface of the leptomeningeal cells of the arachnoidal space. In the contact region between the inner arachnoidal and the outer pial layers the distribution of the RP is similar to the one observed in the interface zone dura mater/arachnoid, while the pial cells themselves are definitely reaction-positive. In all meningeal vessels RP is found at the lumenal and abluminal aspects of the endothelium as well as at the cell membranes of the perivascular cells. These results emphasize the importance of the dural neurothelium for the functions of the blood-cerebrospinal fluid (CSF)-barrier between the dural blood vessels and the CSF.

Electron microscopic study of cat meninges.

The intervascular portions of the encephalic dura mater, arachnoid membrane and pia mater were studied with special reference to their spatial relationships. The cell types were analyzed at electron microscopic level. An outer dural layer, composed of typically elongated fibroblasts and large intercellular spaces was identified. The middle dural layer was composed of collagenous connective tissue matrix together with some fibrocytes scattered in it. The inner dural layer showed epithelium-like arranged cells with light cytoplasm and long processes. The electron-dense band, measuring about 20 nm in width, located between dura mater and arachnoid was not so prominent as in the previously investigated experimental animals. The intercellular contacts among the cells of the outer arachnoid layer included maculae and zonulae adherentes and gap junctions mainly, while the tight junctions observed were quite rare. Following the arachnoid trabecular layer, an inner arachnoid layer could be hardly demonstrated. The pial cells were differentiated into 2 distinct layers, bordering the narrow and discontinuous pial space.

Comparative assessment of articular cartilage and synovial membrane in experimental haemarthrosis.

The changes in articular cartilage and synovial membrane of the knee joints were studied in two groups of rabbits and Wistar rats with experimental haemarthrosis, electron microscopically. Hamarthrosis was produced in group 1 by a single autologous blood injection, in group 2 by intraarticular fracture of the femoral condyles. Samples were taken from the intact articular cartilage, the menisci and the infrapatellar portion of the synovial membrane 12 h to 20 days after intervention. Blood resorption occurs only in the synovial membrane. Fragmentation of erythrocytes and erythrocytophagy by synovial macrophages is documented. The different stages of intracellular digestion of erythrocyte fragments are traced down. Synovial fibroblasts do not participate in erythrocytophagy, although they disclose morphological signs of enhanced functional activity. The findings show changes in the matrix and chondrocytes within the articular cartilage and menisci, and presence of free erythrocytes and lipoprotein complexes amidst the collagen fibres of the matrix. The chondrocytes are poor in cell organelles, while the intracytoplasmic filaments, lipid droplets and glycogen granules are augmented in number. There is no evidence of erythrocytophagy by cartilage cells. On single blood injection in the joint, the ensuing changes are reversible, and the normal synovial membrane structure is restored much quicker than the articular cartilage.