Actin acetylation in Drosophila tissue culture cells

In a permanent cell line derived from Drosophila embryos, cytoplasmic actin is produced as an unstable precursor, which is subsequently converted to a stable form. This conversion results in a reduction in isoelectric point, with no apparent change in molecular weight. The conversion involves an enzymatic acetylation, and results in an insensitivity to aminopeptidase digestion, suggesting N-terminal blockage. Both the acetylated and unacetylated actins can participate in the assembly of F-actin, but with different efficiencies.This work was supported by a grant from the NIH (GM 22866).     

Asymmetric somatic cell hybridization in plants

As part of an investigation into whether it would be possible to use UV radiation as a suitable pretreatment of the donor cells in asymmetric hybridization experiments, the effects of this treatment on sugarbeet (Beta vulgaris L.) protoplast DNA have been determined and compared with those of gamma radiation. Both nuclear and mitochondrial DNAs have been examined. The dose ranges chosen had previously been determined to be potentially applicable for fusion experiments. Pulsed field gel electrophoresis and standard agarose gel electrophoresis have been used in combination with laser scanning densitometry to gain an insight into the precise nature and degree of DNA damage resulting from irradiation. It was observed that UV radiation introduced substantial modifications to sugarbeet DNA. Double-strand breaks were detected, the number of which was found to be directly proportional to the dose applied. Such breaks indicate that UV radiation results in substantial chromosome/chromatid fragmentation in these cells. Chemical modifications to the DNA structure could be revealed by a significant reduction in DNA hybridization to specific mitochondrial and nuclear DNA probes. Following gamma irradiation at equivalent biological doses (i.e. those just sufficient to prevent colony formation) much less damage was detected. Fewer DNA fragments were produced indicating the presence of fewer double-strand breaks in the DNA structure. In comparison to UV treatments, DNA hybridization to specific probes following gamma radiation was inhibited less. For both treatments, mitochondrial DNA appeared more sensitive to damage than nuclear DNA. The possibility that DNA repair processes might account for these differences has also been investigated. Results indicate either that repair processes are not involved in the effects observed or that DNA repair occurs so fast that it was not possible to demonstrate such involvement with the experimental system used. The general relevance of such processes to asymmetric cell hybridization is discussed.     

Does frequency-dependent selection optimize fitness?

In evolutionary biology, the axiom that natural selection tends ideally to maximize inclusive fitness of the individual or some other suitable quantity is often advanced (Cody, 1974; Maynard Smith, 1978; Krebs & McCleery, 1984; Houston et al., 1988). Moreover, the evolutionists generally distinguish two situations (Dawkins, 1980; Maynard Smith, 1982): one in which fitness is independent of the frequency of the phenotypes present in the population (frequency-independent selection), and one in which it does depend on this frequency (frequency-dependent selection). This led some authors such as Parker (1984), and more recently Parker & Maynard Smith (1990), to consider "a 2-speed optimization": frequency-independent selection should lead to a "simple optimum" at the end of the selective process, since all the individuals should have the same strategy and the mean fitness of the population should be maximized; frequency-dependent selection, formulated in terms of the theory of games, should lead to a "competitive optimum" even though the "evolutionary stable strategy" (or "ESS"; Maynard Smith & Price, 1973) characterizing the equilibrium "is not the strategy that maximizes fitness in a population sense" (Parker & Maynard Smith, 1990: 30). Our aim in this short communication is to criticize the concept of "competitive optimum" by Parker & Maynard Smith, as well as the general ability of natural selection to "maximize fitness", even in "phenotypic models" (Lloyd, 1977). These models, devoid of genetic constraints since each strategist is assumed to reproduce its own kind, are especially suitable for examining the ideal effect of natural selection.     

In-vitro activity of miltefosine and voriconazole on clinical isolates of free-living amebas: Balamuthia mandrillaris, Acanthamoeba spp., and Naegleria fowleri

The anticancer agent miltefosine and the antifungal drug voriconazole were tested in vitro against Balamuthia mandrillaris, Acanthamoeba spp., and Naegleria fowleri. All three amebas are etiologic agents of chronic (Balamuthia, Acanthamoeba) or fulminant (Naegleria) encephalitides in humans and animals and, in the case of Acanthamoeba, amebic keratitis. Balamuthia exposed to <40 microm concentrations of miltefosine survived, while concentrations of >or=40 microM were generally amebacidal, with variation in sensitivity between strains. At amebastatic drug concentrations, recovery from drug effects could take as long as 2 weeks. Acanthamoeba spp. recovered from exposure to 40 microM, but not 80 microM miltefosin. Attempts to define more narrowly the minimal inhibitory (MIC) and minimal amebacidal concentrations (MAC) for Balamuthia and Acanthamoeba were difficult due to persistence of non-proliferating trophic amebas in the medium. For N. fowleri, 40 and 55 microM were the MIC and MAC, respectively, with no trophic amebas seen at the MAC. Voriconazole had little or no inhibitory effect on Balamuthia at concentrations up to 40 microg/ml, but had a strong inhibitory effect upon Acanthamoeba spp. and N. fowleri at all drug concentrations through 40 microg/ml. Following transfer to drug-free medium, Acanthamoeba polyphaga recovered within a period of 2 weeks; N. fowleri amebas recovered from exposure to 1 microg/ml, but not from higher concentrations. All testing was done on trophic amebas; drug sensitivities of cysts were not examined. Miltefosine and voriconazole are potentially useful drugs for treatment of free-living amebic infections, though sensitivities differ between genera, species, and strains.     

Evidence of silver eels contamination by microcystin‐LR at the onset of their seaward migration: what consequences for breeding potential?

Thirty migrating silver eels Anguilla anguilla were collected in a river system where algal blooms occurred yearly. Fifty per cent of eel livers were contaminated by microcystin-LR (mean ± s . d . toxin level: 28·1 ± 22·4 ng g⁻¹). Contaminated silver ( v. healthy) eels had lower fish condition. Consequences of this impact for the breeding potential of these migrating eels are discussed.     

Life History Studies on the Genus Trillium (Liliaceae) V. Reproductive Biology and Survivorship of Three Declinate-flowered Species

Absract Three pedicellate-declinate-flowered species of Trillium (Liliaceae), T. vaseyi and T. flexipes , were studied for their life history characteristics, e.g., stage class structures of natural populations and reproductive features, including energy allocation to reproductive activities. The populations structures of all three species showed similar depletion structures characterized by a conspicuous decrease of individuals in the small juvenile stages, as was also observed in pedicellate-erect-flowered Trillium species However, with respect to reproductive characteristics, these three declinate-flowered species showed different features from erect-flowered species, although they belong to the same pedicellate-flowered group. That is, these declinate-flowered Trillium species exhibited low seed setting rates of 30% in T. catesbaei , 45% in T. vaseyi and 34% in T. flexipes , suggesting that they possess different mating systems from erect-flowered species which showed high seed setting rates of 50–90%.     

Study of the in vitro bioactivation of albendazole in human liver microsomes and hepatoma cell lines

The metabolism of albendazole (ABZ), a benzimidazole anthelminthic, was studied in either microsomal preparations of human liver biopsies or cultured human hepatoma cell lines. Metabolites were analyzed by HPLC. Our data show that microsomes from human biopsies and two human cell lines, HepG2 and Hep3B, oxidize the drug to the sulfoxide very efficiently, whereas the third cell line tested, SK-HEP-1, does not. Both cytochrome P-450 dependent monooxygenases and favin-containing monooxygenases appear to be involved in human ABZ metabolism. Using the cell line displaying the highest ABZ-metabolizing activity, HepG2, the cytotoxic and the inducing effects of the parent drug ABZ and of two primary metabolites, the sulfoxide and the sulfone were studied. These three chemicals provoked a rise in mitotic index resulting from cell division blockage at the prophase or at the metaphase (ABZ metabolites) stage, and ABZ was more cytotoxic than its metabolites. With regard to enzyme-inducing effects, our data clearly demonstrate that the sulfoxide and, to a lesser degree, the sulfone are potent inducers of some drug metabolizing enzymes (i.e., cytochrome P-488 dependent monooxygenases and UDP glucuronyltransferase), whereas ABZ fails to increase and even slightly decreases these enzymatic activities. In conclusion, the HepG2 human hepatoma cell line appears to be suitable for the study of many parameters of metabolism and action of ABZ and other structurally related compounds in humans.Abbreviations ABZ albendazole - B[a]P benzo[a]pyrene - HPLC high-performance liquid chromatography - MC 3-methylcholanthrene - MFO mixed-function oxidase - UDPGT UDP-glucuronyltransferase     

Sensitivity to low-dose/low-LET ionizing radiation in mammalian cells harboring mutations in succinate dehydrogenase subunit C is governed by mitochondria-derived reactive oxygen species

It has been hypothesized that ionizing radiation-induced disruptions in mitochondrial O? metabolism lead to persistent heritable increases in steady-state levels of intracellular superoxide (O?(?U+2212)) and hydrogen peroxide (H?O?) that contribute to the biological effects of radiation. Hamster fibroblasts (B9 cells) expressing a mutation in the gene coding for the mitochondrial electron transport chain protein succinate dehydrogenase subunit C (SDHC) demonstrate increases in steady-state levels of O??- and H?O?. When B9 cells were exposed to low-dose/low-LET radiation (5-50 cGy), they displayed significantly increased clonogenic cell killing compared with parental cells. Clones derived from B9 cells overexpressing a wild-type human SDHC (T4, T8) demonstrated significantly increased surviving fractions after exposure to 5-50 cGy relative to B9 vector controls. In addition, pretreatment with polyethylene glycol-conjugated CuZn superoxide dismutase and catalase as well as adenoviral-mediated overexpression of MnSOD and/or mitochondria-targeted catalase resulted in significantly increased survival of B9 cells exposed to 10 cGy ionizing radiation relative to vector controls. Adenoviral-mediated overexpression of either MnSOD or mitochondria-targeted catalase alone was equally as effective as when both were combined. These results show that mammalian cells over expressing mutations in SDHC demonstrate low-dose/low-LET radiation sensitization that is mediated by increased levels of O??- and H?O?. These results also support the hypothesis that mitochondrial O??- and H?O? originating from SDH are capable of playing a role in low-dose ionizing radiation-induced biological responses.     

Recent Developments in Optical Neuromodulation Technologies

The emergence of optogenetics technology facilitated widespread applications for interrogation of complex neural networks, such as activation of specific axonal pathways, previously found impossible with electrical stimulation. Consequently, within the short period of its application in neuroscience research, optogenetics has led to findings of significant importance both during normal brain function as well as in disease. Moreover, the optimization of optogenetics for in vivo studies has allowed the control of certain behavioral responses such as motility, reflex, and sensory responses, as well as more complex emotional and cognitive behaviors such as decision-making, reward seeking, and social behavior in freely moving animals. These studies have produced a wide variety of animal models that have resulted in fundamental findings and enhanced our understanding of the neural networks associated with behavior. The increasing number of opsins available for this technique enabled even broader regulation of neuronal activity. These advancements highlight the potential of this technique for future treatment of human diseases. Here, we provide an overview of the recent developments in the field of optogenetics technology that are relevant for a better understanding of several neuropsychiatric and neurodegenerative disorders and may pave the way for future therapeutic interventions.