Localization of a nuclear envelope-associated protein by indirect immunofluorescence microscopy using antibodies against a major polypeptide from rat liver fractions enriched in nuclear envelope-associated material

The location of a specific major polypeptide present in nuclear pore complex-enriched fractions from rat liver was examined by indirect immunofluorescence microscopy using chicken antibodies against this polypeptide. In both whole cell preparations of cultured cells grown on cover slips (mouse 3 T 3, rat kangaroo PtK2) and in frozen sections through liver and mammary gland tissue a strongly preferential, if not exclusive, binding to the nuclear periphery of interphase cells was observed. The specificity of this localization was demonstrated in these cells by the decoration of chromatin with antibodies against histones and of elements of the endoplasmic reticulum--outer mitochondrial membrane--system with antibodies to cytochrome b5. In addition, the localization was examined by electron microscopy using frozen sections and "immunoperoxidase" techniques. The results suggest that this polypeptide is contained in a protein specific for the nuclear periphery, probably closely associated with the peripheral chromatin.

The dissociation of nuclear proteins from superhelical DNA

Structures retaining many of the morphological features of nuclei may be released by gently lysing human cells in solutions containing non-ionic detergents and high concentrations of salt. These nucleoids contain superhelical DNA. Using a double-labelling procedure we have compared, at different salt concentrations, the amounts and types of protein associated with human nucleoides containings superhelical or relaxed DNA. We find that the slightly lysine-rich histones (H2A and H2B) but not the arginine-rich histones (H3 and H4) dissociate more slowly from nucleoids containing superhelical DNA than from those containing relaxed DNA. A protein of apparent molecular weight of 22000 also binds more tightly to superhelical DNA. We conclude that this protein and the slightly lysine-rich histones transmute free energy of supercoiling into binding energy when they bind to superhelical DNA.

Characterization of nuclear structures containing superhelical DNA

Structures resembling nuclei but depleted of protein may be released by gently lysing cells in solutions containing non-ionic detergents and high concentrations of salt. These nucleoids sediment in gradients containing intercalating agents in a manner characteristic of DNA that is intact, supercoiled and circular. The concentration of salt present during isolation of human nucleoids affects their protein content. When made in I-95 M NaCl they lack histones and most of the proteins characteristic of chromatin; in 1-0 M NaCl they contain variable amounts of histones. The effects of various treatments on nucleoid integrity were investigated.

Affinity chromatography of DNA-binding proteins from human, murine and man-mouse hybrid cell lines

About 60 proteins from human and murine cell lines were isolated by their ability to bind to different preparations of DNA. In the intact cell, the majority of these proteins are to be found in the cell nucleus. The electrophoretic mobilities of the DNA-binding proteins from human, murine and man-mouse hybrid cell lines were compared in two-dimensional acrylamide gels. Few, if any, species-specific differences were found. These observations suggest that the structures of the vast majority of the proteins that interact with DNA are conserved through evolution. A molecular basis is thus provided for the intracellular of hybrid cells derived from different animal species.

Meiosis in the male of Culex pipiens and Aedes albopictus and fertilization in the Culex pipiens-complex

As a result of close somatic pairing of the chromosomes visible leptotene stages do not occur in either Culex pipiens or Aedes albopictus. Bouquet stages were not observed during early meiotic prophase. The sperm of C. pipiens consist of a head 14 μ long and a tail 200 μ long. More than 80% of sperm treated with 3H-Tdr could be sufficiently labeled by feeding fourth instar larvae 10 μCi/ml/larva 3H-Tdr for about 3 days. An almost complete label could be found in the sperm head and only some few grains in the DNA of the mitochondrial bodies of the tail.In the C. pipiens female, meiosis is activated by the entrance of the sperm and karyogamy is effected about 50 minutes after oviposition. During the meiotic divisions the sperm moves to the center of the egg and fuses with the pronucleus. If supernumerary sperm are present they most often are found near the micropylar pole of the egg.Although the frequency of polyspermy is low, one or two sperm are usually present in the fertilized eggs.In incompatible crosses with strains of different geographical origins (♂ Hamburg ♀ Paris) the egg is activated by the sperm and the meiotic divisions begin but the sperm does not succeed in fusing with the pronucleus. The developing embryos are haploid and embryogenesis leads to irregular differentiation; 99.9% of the embryos die. Apparently reactions between sperm and egg cytoplasm prevent karyogamy. The different models of cross-reactions in the C. pipiens-complex are discussed; mitochondrial DNA is suggested to be involved in fertilization.

[Genetic investigations on the incompatibility in the Culex pipiens complex]

In crosses between populations of the mosquito Culex pipiens of different geographical origin three crossing types have been found (1) crosses with normal offspring (2) crosses with reduced offspring and (3) crosses that show almost total incompatibility. In the case of incompatible crosses 99.9% of the developing embryos are lethal and only about 0.1% of the embryos hatch and develop into fertile diploid females. The origin of the exceptional diploid females has been investigated by means of the marker genes Kuf, r, w, var, y and ru. These females develop from a diploid oocyte or from a diploid nucleus that originated by fusion of the pronucleus and the last polar body. This has been concluded from the frequency of homozygous and heterozygous offspring from heterozygous females, the frequency of equational separation of different genes and the distribution of cross-over gametes in the exceptional females. Based on the genetical data it is argued that induced meiotic parthenogenesis takes place. The sperm does not play any part in the production of the diploid females and the lethal embryos. After the activation of the egg the sperm moves to the center of the egg but it does not succeed to fuse with the pronucleus. As a result the pronucleus starts to develop into a haploid embryo in about 99.9% and only in a few cases is the diploidy restored by a change in the meiotic process in the egg.