Segmentation and moral status in vivo and in vitro: a scientific perspective

A basic consideration in research on human embryos is the controversy about when the embryo acquires moral status. The author refutes the contention that segmentation is the determinant of moral status. She notes that segmentation, as a stage in embryonic development, does not coincide with the development of "irreversible individuality" upon which the segmentation argument depends. Dawson also finds a lack of clarity in the meaning of "individuality." These problems, she maintains, prevent segmentation from being morally important and render the proposed 14-day limit on embryo research unnecessary. Dawson concludes that to introduce a time restriction on embryo research is premature because it is based on an inadequate philosophical argument.     

A review of the molecular basis of hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency

Hypoxanthine-guanine phosphoribosyltransferase (HPRT, EC 2.4.2.8) is a purine salvage enzyme that catalyses the conversion of hypoxanthine and guanine to their respective mononucleotides. Partial deficiency of this enzyme can result in the overproduction of uric acid leading to a severe form of gout, whilst a virtual absence of HPRT activity causes the Lesch-Nyhan syndrome which is characterised by hyperuricaemia, mental retardation, choreoathetosis and compulsive self-mutilation. The HPRT-encoding gene is located on the X chromosome in the region q₂₆–q₂₇ and consists of nine exons and eight introns totalling 57 kb. This gene is transcribed to produce an mRNA of 1.6 kb, which contains a protein encoding region of 654 nucleotides. With the advent of increasingly refined techniques of molecular biology, it has been possible to study the HPRT gene of individuals with a deficiency in HPRT activity to determine the genetic basis of the enzyme deficiency. Many different mutations throughout the coding region have been described, but in the absence of precise information on the three-dimensional structure of the HPRT protein, it remains difficult to determine any consistent correlation between the structure and function of the enzyme.     

Effects of spines and thorns on Australian arid zone herbivores of different body masses

Summary We investigated the effects of thorns and spines on the feeding of 5 herbivore species in arid Australia. The herbivores were the rabbit (Oryctolagus cuniculus), euro kangaroo (Macropus robustus), red kangaroo (Macropus rufus), sheep (Ovis aries), and cattle (Bos taurus). Five woody plants without spines or thorns and 6 woody plants with thorns were included in the study. The spines and thorns were not found to affect the herbivores' rates of feeding (items ingested/min), but they did reduce the herbivores' rates of biomass ingestion (g-dry/item). The reduction in biomass ingested occurred in two ways: at a given diameter, twigs with spines and thorns had less mass than undefended plants, and the herbivores consumed twigs with smaller diameters on plants with spines and thorns. The relative importance of the two ways that twigs with spines and thorns provided less biomass varied with herbivore body mass. Reduced twig mass was more important for small herbivores, while large herbivores selected smaller diameters. The effectiveness of spines and thorns as anti-herbivore defenses did not vary with the evolutionary history of the herbivores (i.e. native vs. introduced). Spines and thorns mainly affected the herbivores' selection of maximum twig sizes (reducing diameter and mass), but the minimum twig sizes selected were also reduced.     

中国平脉树螽属五新种记述：直翅目：螽斯科：树螽亚科

本文报道中国平脉树螽属5个新种。每个新种皆有详细的形态描述和形态特征图。所有模式标本存于北京农业大学昆虫标本室。     

Immunocytochemical localization of transient DNA strand breaks in differentiating myotubes using in situ nick-translation

We have localized DNA strand breaks during in vitro chicken myogenesis by repairing nicks in nuclei of fixed cell monolayers in situ with biotin-11-dUTP, followed by immunocytochemical detection of incorporated biotin with rabbit anti-biotin and FITC-labeled goat anti-rabbit antibodies. No accumulations of biotin sufficient for immunocytochemical detection were observed in 23-hr cultures of dividing cells. In 33- and 43-hr cultures, biotin was first detected in only 3% of the nuclei, all of which appeared to be in fusing myoblasts or small myotubes. In contrast, cultures of young, highly fused myotubes (56 hr) exhibited 18% biotinylated nuclei; virtually all of these nuclei, most of which were grouped as aggregates, were within myotubes. In older cultures (73 and 94 hr) incorporation of biotin into myotube nuclei markedly decreased, while increases were noted in nuclei of mononuclear cells. These results indicate that extensive single-stranded DNA nicking occurs in nuclei of young myotubes, followed by repair as terminal differentiation ensues.     

Effects of chelating agents on the Ca2+-stimulated ATPase of rat liver plasma membranes

Using strictly controlled ionic conditions we have demonstrated, in agreement with previous findings (Lotersztajn et al. (1981) J. Biol. Chem. 256, 11209-11215; Lotersztajn, S. and Pecker, F. (1982) J. Biol. Chem. 257, 6638-6641) a Ca2+-stimulated ATPase in rat liver plasma membranes which is detectable at low free Mg2+ concentrations (normally fulfilled by endogenous levels) but not at free Mg2+ concentrations greater than about 10(-5) M. The findings reported here also suggest that this (Ca2+ + Mg2+)-ATPase is activated by EGTA or one of its liganded species. Furthermore, this is probably an intrinsic property of the enzyme as it was found to be independent of the isolation technique. The stimulation by EGTA appears to be a function both of free Ca2+ concentration and of one or more liganded species of EGTA and it is also inhibited at high free Mg2+ concentrations (approx. 10(-5) M). The specificity of the EGTA effect on ATPase activity is studied with respect to other, widely used, chelating agents namely HEEDTA, EDTA and CDTA. Of these, only CDTA shares the effect, although the concentration dependence of the activation is different from EGTA, suggesting that there is some degree of structural specificity involved rather than a generalised effect of complexed Ca2+.     

X-Linked Female-Sterile Loci in DROSOPHILA MELANOGASTER

We have examined the number of X-linked loci specifically required only during oogenesis. Complementation analyses among female-sterile (fs) mutations obtained in two mutagenesis screens--GANS' and MOHLER's--indicate that any fs locus represented by two or more mutant alleles in GANS' collection are usually present in MOHLER's collection. However, when a locus is represented by a single allele in one collection, it is generally not present in the other collection. We propose that this discrepancy is due to the fact that most "fs loci" represented by less than two mutant alleles are, in fact, vital (zygotic lethal) genes, and that the fs alleles are hypomorphic mutations of such genes. In support of this hypothesis we have identified lethal alleles at 12 of these "fs loci." The present analysis has possibly identified all maternal-effect lethal loci detectable by mutations on the X chromosome and has allowed us to reevaluate the number of "ovary-specific fs" loci in the Drosophila genome. Finally, germline clone analysis of a large number of fs mutations was performed in order to estimate the relative contribution of germline and somatic cell derivatives to oogenesis and to embryonic development. All the maternal-effect lethal loci tested are germline-dependent.     

Amino acid sequence data of alpha-tubulin from myxamoebae of Physarum polycephalum

About 96% of the amino acid sequence of an alpha-tubulin from the slime mould Physarum polycephalum has been determined. Of 430 sequenced amino acids, 30 differ from the deduced amino acid sequence of a recently published alpha-tubulin complementary DNA from the plasmodial form of P. polycephalum. The myxamoebal alpha-tubulin differs from all other known alpha-tubulins in one of the last three C-terminal amino acids that are Gly-Glu-Tyr instead of the usual Glu-Glu-Tyr. These last three amino acids are preceded by 11 residues that appear to be particularly susceptible to mutation. No heterogeneity was found whilst sequencing the myxamoebal alpha-tubulin, indicating that only one type of alpha-tubulin is present in myxamoebae. This alpha-tubulin appears to be less conserved than the previously described plasmodial alpha-tubulin, supporting the hypothesis that the structural constraints on tubulin in axonemes have a significant effect on its rate of mutation.