Changes in the histones of the sea urchin Strongylocentrotus purpuratus at fertilization

Both sperm and eggs of the sea urchin Strongylocentrotus purpuratus contain specific histones in place of some of the histones found during later development. Whether these specific histones are lost upon fertilization or are retained is not known. Therefore, we have examined the histones present in the zygote nucleus to determine the fate of the gamete histones. Nuclei of zygotes which have completed DNA replication in preparation for the first mitosis were isolated by sucrose density gradient centrifugation. Histones were extracted from the isolated nuclei, and were analyzed by acid-urea and SDS polyacrylamide gel electrophoreses, and by two-dimensional electrophoresis in which both gel electrophoresis systems were combined. Electrophoretic patterns of the zygote histones were compared with those of sperm, unfertilized eggs and embryos. The results show that the zygote histone pattern is identical with the unfertilized egg histone pattern. Neither the sperm histones H1, H2A, or H2B, nor the embryonic H1, H2A, or H2B, are present in the zygote pattern. The egg and the zygote do contain a unique H2A and H2B, but not an H1. After fertilization, sperm specific histones are not present on the DNA. Egg histones become associated with both the sperm DNA and the newly replicated DNA. The association of the embryonic histones with the DNA, therefore, occurs sometime later in development.     

Lévi-Strauss on the Oedipus Myth: A Reconsideration

The first half of the article presents a critique of Lévi-Strauss' well-known analysis of the Oedipus myth. A consideration of Greek beliefs suggests that Lévi-Strauss is incorrect in tying certain events in that myth to the "overvaluation of blood relations" and in asserting that the myth is concerned with the "affirmation/denial of man's autochthonous origins." The second half of the article presents a different structural analysis of the entire Theban Saga, of which the Oedipus myth is but a part. It concludes (1) that Lévi-Strauss is correct in identifying a series of events in the myth which indicate the devaluation of blood relations, but that these events specifically refer to the devaluation of patrilineal kin ties and that the range of events indicating the devaluation of patrilineal ties is broader than his analysis would suggest, and (2) there is another series of repeated events (unmentioned by Lévi-Strauss) which indicates the affirmation of patrilineal kin ties. The final hypothesis— that the opposition between the devaluation/affirmation of patrilineal kin ties underlies the Theban Saga— "makes sense" in terms of Greek history, as the period in which the Olympian myths look their present form is also the period in which the Greeks moved from a society organized along patrilineal kin ties to one organized around allegiance to the polis. [structuralism, Oedipus myth, myth and social structure, Lévi-Strauss, anthropological theory]     

The cell-wall phosphatase of cotton (Gossypium) is inhibited by kelthane.

Kelthane [4,4'-dichloro-alpha-(trichloromethyl)benzhydrol] was previously shown to decrease the limited tolerance of susceptible varieties of cotton (Gossypium) to Verticillium wilt. Kelthane was shown in the present study to inhibit the cell-wall p-nitrophenyl phosphatase of cotton. In view of information already establishing the cell wall as a primary site of action of Verticillium wilt, the data are interpreted as suggesting an as yet undefined interaction between Kelthane, cell-wall phosphatase and verticillium-resistance mechanisms of the cell wall.     

Adjacent repeating units of xenopus laevis 5S DNA can be heterogeneous in length

The distribution of length heterogeneity in adjacent repeating units of X. laevis 5S DNA has been examined by “cloning” 5S DNA in bacteria. Fragments of 5S DNA produced by partial digestion with Hind III and containing 1, 4, and 5 repeating units have been inserted at the single Hind III site of the tetracycline-resistance plasmid, pSC101, and the hybrid plasmids cloned in E. coli. Adjacent 5S DNA repeats in the cloned multi-repeat fragments can differ in length. This finding rules out some mechanisms which have been proposed to account for the parallel evolution of tandem repeated DNAs. The results are consistent with an unequal crossing-over mechanism and place some constraints on the molecular processes in this recombinatory event.     

RELATIVE IMPORTANCE OF CHOLINE TRANSPORT TO SPONTANEOUS AND POTASSIUM DEPOLARIZED RELEASE OF ACh

—The importance of extracellular choline transport to spontaneous and K⁺ depolarized release of ACh was studied using mouse brain cortex minces. The results suggest that extracellular choline transport is not essential to spontaneously released ACh but is essential to K⁺ depolarized ACh release. Similar cumulative amounts of choline and ACh were found in the incubation media following incubation of minces in either Krebs or 35 mm -K⁺ Krebs suggesting the same production of free choline during both conditions. Double reciprocal plots of choline accumulation by non-depolarized cortex minces yield high and low affinity components. Conversely, similar analysis of choline accumulation by depolarized minces yields a single Michaelis constant (68 μm ) similar to the low affinity (50 μm ) Michaelis constant determined for choline accumulation by non-depolarized minces. Kinetic analysis of ACh release as a function of extracellular choline concentration during K⁺ depolarization also yields a Michaelis constant of 68 μm These data suggest a link between choline transport and ACh release during K⁺ depolarization.     

REGIONAL DIFFERENCES IN HIGH AFFINITY CHOLINE TRANSPORT VELOCITY IN GUINEA-PIG BRAIN

The kinetic parameters of choline accumulation by synaptosomes prepared from different regions of guinea-pig brain (cortex, brainstem, and cerebellum) were determined. Choline was accumulated by a high affinity transport process for all regions tested and the apparent Michaelis constants were similar. However, the apparent maximal velocities of choline accumulation for the brain regions differed; the differences were related to the amount of acetylcholine formed by the respective regions. The results suggested that the maximal velocity of the high affinity transport process may reflect the density of cholinergic nerve endings within brain regions.     

The toxicity of tritium: the effects of tritiated amino-acids on preimplanted mouse embryos

The effects of tritiated amino-acids, arginine, lysine, histidine and aspartic acid on the growth and development of two-cell mouse embryos, cultured in vitro, were investigated. The LD50 for the dibasic amino acids, measured on the third day of growth, ranged from 30 to 130 nCi/ml. This was compared with the DNA precursor, thymidine, for which the LD50 was 80 nCi/ml.     

Down-regulation of miR-17 family expression in response to retinoic acid induced neuronal differentiation

Whole-genome microRNA and gene expression analyses were used to monitor changes during retinoic acid induced differentiation of neuroblasts in vitro. Interestingly, the entire miR-17 family was over-represented among the down-regulated miRNA. The implications of these changes are considerable, as target gene prediction suggests that the miR-17 family is involved in the regulation of the mitogen-activated protein kinase (MAPK) signaling pathway, synaptic plasticity and other markers of neuronal differentiation. Significantly, many of the target responses predicted by changes in miRNA expression were supported by the observed changes in gene expression. As expected, markers of neuronal differentiation such as anti-apoptotic protein B-cell lymphoma 2 (BCL2), myocyte enhancer factor-2D (MEF2D) and zipper protein kinase (MAP3K12; aka ZPK/MUK/DLK) were each up-regulated in response to differentiation. The expression of these genes was also reduced in response to miR-17 and miR-20a transfection, and more specifically they were also shown to contain functional miRNA recognition elements for members of the miR-17 family by reporter gene assay. This suggests that the miR-17 family have an integral role in fine-tuning the pathways involved in the regulation of neuronal differentiation.