Robust Selection of the Most Discriminative Variables in the Dichotomous Problem with Application to Some Respiratory Disease Data

A robust method for selection of variables with the greatest discriminatory power is presented in the paper. The method deals with the two groups of data problem. An application of the method to some respiratory disease data and comparisons with classical procedures are given, also.     

Macromolecular synthesis in organ cultures of neonatal rat lung

Organ cultures of newborn rat lungs synthesize and accumulate DNA, RNA, collagen and noncollagenous proteins almost at a linear rate for at least 5 days. During this period the synthesis of collagen consistently exceeds the synthesis of noncollagenous proteins in a pattern similar to neonatal lung growth in vivo. Although some morphological characteristics of lung architecture are distorted after culture, fundamental structural similarities to lungs growing in intact animals are retained. When these cultures are maintained in atmospheres rich in oxygen, increased collagen synthesis is observed, a response similar to that of lungs in intact animals exposed to high oxygen concentrations in vivo. Our studies suggest that lung organ cultures may be a suitable system for investigating the biochemical aspects of lung tissue-environmental interaction. These studies were supported in parts by NIH Grant HL-19668, a contract (68-03-2005) from the U.S. Environmental Protection Agency, and grants from the California Lung Association.     

Field studies on the population dynamics of Biomphalaria glabrata, intermediate host of Schistosoma mansoni on the West Indian Island of St. Lucia

Growth curves, calculated for field populations of B. glabrata, were not materially affected by habitat, altitude or season. A mean growth curve was therefore used to estimate the age-frequency distribution of snails in successive field samples. These data permitted the construction of ecological life tables and the estimation of r, the intrinsic rate of natural increase (or decrease) of the different populations. The calculated values of r were inserted in a simple model of unlimited population growth but the resultant curves poorly represented the observed data. A model for unlimited growth was more satisfactory for pond and marsh populations but, apparently, immigration made it less satisfactory for stream and banana drain populations. Nevertheless, r may still be of value in predicting repopulation rates in certain habitats after a mollusciciding which does not kill the entire snail population.     

Fine structure of early human embryos frozen with 1,2 propanediol

Previous studies by a French group (Fertil Steril 44:645–651, 1985) have shown that two-to eight-cell human embryos can survive slow freeze-thawing with propanediol in a biological freezer. These embryos were assessed for morphological appearance by phase-contrast microscopy. We assessed the structure of 25 frozen-thawed one- to 12-cell embryos, obtained from our in vitro fertilization (IVF) and GIFT programmes, by phase-contrast and electron microscopy, using the same method of cryopreservation. One-fourth of the embryos examined had all cells intact, and more than one-half the embryos had over 50% of their cells well preserved. Some of these embryos had unequal blastomeres and cytoplasmic fragments. Ultrastructural assessment revealed good preservation of fine structure in the intact blastomeres of all embryos and maintenance of cell-to-cell contacts. Most cytoplasmic organelles, cell membranes, and nuclei were well preserved compared to nonfrozen controls. The cells that were cryoinjured showed varying degrees of disorganization of the cell membrane, cytosol, and cellular membranes, including swelling and disruption of the nuclear envelope. Disruption of the zona was somewhat rare. Small cytoplasmic fragments were less prone to cryoinjury than blastomeres. The use of propanediol for embryo cryopreservation seems to be feasible; frozen embryos with more than 50% cells intact have produced 10 pregnancies after embryo transfer (Fertil Steril 46:268–272, 1986). Replacement of 17 frozen embryos in seven patients has resulted in a twin pregnancy in Singapore. However, the effects of freezing on the mitotic spindles of embryonic cells need to be investigated further.     

In vitro rooting of the apple rootstock M 26 in adult and juvenile growth phases and acclimatization of the plantlets

In order to obtain optimum conditions for in vitro propagation of the apple rootstock M 26 ( Malus pumila Mill.) in adult and juvenile growth phases, several rooting experiments were performed. Supraoptimal concentrations of indole-3-butyric acid (IBA) added to the rooting media resulted in profuse callus formation. Since extensive callus production is detrimental to the survival of the plantlets, modified culture conditions were established to reduce callus formation. A reduction of the time of exposure to IBA to 5 days and, thereafter, transfer to a hormone-free medium did not eliminate callus production. Exposure to darkness during the root initiation phase increased rooting. When the rooting medium was based on the Lepoivre formula instead of the Murashige and Skoog formula, callus formation was reduced. Optimum conditions for rooting were obtained at much lower concentration than earlier reported, being 1.25 μM for the juvenile and 0.5 μM for the adult growth phase in the range of IBA concentrations tested. Anatomical studies revealed that root initials are formed after 5 days of IBA-treatment. Therefore, we transferred shoots directly to non-sterile conditions after the root-inducing phase. This resulted in a 90% survival of the plantlets. Subculture on hormone-free medium can thus be eliminated when the optimum auxin concentration is known.     

Statistical evidence for remnants of the primordial code in the acceptor stem of prokaryotic transfer RNA

Summary The specificity of interaction of amino acids with triplets in the acceptor helix stem of tRNA was investigated by means of a statistical analysis of 1400 tRNA sequences. The imprint of a prototypic genetic code at position 3–5 of the acceptor helix was detected, but only for those major amino acids, glycine, alanine, aspartic acid, and valine, that are formed by spark discharges of simple gases in the laboratory. Although remnants of the code at position 3–5 are typical for tRNAs of archaebacteria, eubacteria, and chloroplasts, eukaryotes do not seem to contain this code, and mitochondria take up an intermediary position. A duplication mechanism for the transposition of the original 3–5 code toward its present position in the anticodon stern of tRNA is proposed. From this viewpoint, the mode of evolution of mRNA and functional ribosomes becomes more understandable.Offprint requests to: W. Moller     

Cytokinin-binding proteins

This article is focused on the modalities of reception of cytokinins which remain largely unknown. It summarizes the main steps of the different protocols used to study cytokinin-binding proteins (CBPs). We place emphasis on the significance and specificity of the detection according to the properties of the probes used: radioactive or photoreactive cytokinins, fluorescent anticytokinins, anti-idiotype antibodies. The purification procedures are also examined. The cellular localisation and the putative physiological roles of the numerous and different CBPs found are considered. The interest of genetic and molecular studies is discussed.     

Influence of retinoids and EGF on growth of embryonic mouse palatal epithelia in culture

Summary Retinoids and growth factors seem to be important for normal mammalian reproduction and development. High levels of retinoic acid are teratogenic and induce cleft palate in the mouse. Little is known concerning the mechanisms through which retinoids induce cleft palate. Palatal epithelia from CD-1 embryonic mice on Day 12 of gestation were isolated from the mesenchyme and cultured in serum-free media, with all-trans retinoic acid or 13-cis retinoic acid, with or without epidermal growth factor (EGF). The epithelia attached and grew, and the cells differentiated over a 72-h culture period. Binding of [¹²⁵I]EGF was observed in all cultures in a pattern that correlated with thymidine (TdR) uptake by the epithelia. EGF enhanced growth and [³H]TdR incorporation of the oral cells, but nasal cells generally did not proliferate. In this culture system, both retinoids suppressed [³H]TdR incorporation in a concentration-dependent manner for epithelia cultured with or without EGF. Medial cells are important to normal palatogenesis as they play a role in fusion of opposing shelves and subsequently many of these cells undergo programmed cell death. Death of medial cells in vitro is prevented by EGF and by the retinoids, either with or without EGF. This response occurs in the absence of a mesenchymal interaction, suggesting that the medial cell response to EGF and retinoids is not mediated by or dependent on the mesenchymal tissues. The survival of medial cells may be responsible for the failure of opposing shelves to fuse.     

Senescence in cut carnation flowers: Temporal and physiological relationships among water status, ethylene, abscisic acid and membrane permeability

Changes in water status, membrane permeability, ethylene production and levels of abscisic acid (ABA) were measured during senescence of cut carnation flowers ( Dianthus caryophyllus L. cv. White Sim) in order to clarify the temporal sequence of physiological events during this post-harvest period. Ethylene production and ABA content of the petal tissue rose essentially in parallel during natural senescence and after treatment of young flowers with exogenous ethylene, indicating that their syntheses are not widely separated in time. However, solute leakage, reflecting membrane deterioration, was apparent well before the natural rise in ethylene and ABA had begun. In addition, there were marked changes in water status of the tissue, including losses in water potential (ψ_w), and turgor (ψ_p), that preceded the rise in ABA and ethylene. As senescence progressed, ψ_w continued to decline, but ψ_p returned to normal levels. These temporal relationships were less well resolved when senescence of young flowers was induced by treatment with ethylene, presumably because the time-scale had been shortened. Thus changes in membrane permeability and an associated water stress in petal tissue appear to be earlier symptoms of flower senescence than the rises in ABA or ethylene. These observations support the contention that the climacteric-like rise in ethylene production is not the initial or primary event of senescence and that the rise in ABA titre may simply be a response to changes in water status.