Protein serine/threonine phosphatases as binding proteins for okadaic acid

Recently, many potent inhibitors of protein serine/threonine phosphatases (PPs) have been found. Some of them have proven to be tumor promoters in mouse skin two-step carcinogenesis and rat liver medium-term tests. Among these inhibitors, okadaic acid (OA) selectively inhibits PP2A, and its use has therefore been proposed to facilitate analysis of biological roles of this phosphatase. OA shows bimodal effects on in vitro transformation and, in addition to such epigenetic changes, also induces marked genetic changes. OA treatment for more than 1 week flattened NIH 3T3 transformants irreversibly, with loss of the transfected genes. It is also known to induce diphtheria toxin-resistant mutations in Chinese hamster lung cells and sister chromatid exchanges (SCEs) in Chinese hamster ovary cells and human lymphocytes. To analyze roles of protein phosphatases in gene stability, we isolated OA-resistant mutants. They were proven to have a mutation in the PP2A catalytic subunit, in which cysteine 269 had beensubstituted for glycine; and it was demonstrated that this region interacts with OA. The recombinant mutant protein was 4 9-fold more resistant to OA than the wild type. Although the OA resistant mutants of CHO cells expressed high levels of P-glycoprotein, inhibition of PP2A itself was suggested to lead to SCE induction. However, the number of molecular species of PP which are known to be sensitive to OA continues to increase, and we have isolated cDNA for a novel type of OA sensitive PP. Our studies indicate that the fact that the roles of PP2A cannot be elucidated using only OA is of crucial importance.     

Phyllodied panicles caused by head smut of maize and vegetative multiplication of maize

Young in vitro cultured panicles of maize(Zea mays L.) isolated from plants previously infected under controlled conditions by Sporisorium reilianum (Kühn) Landon and Fullerton, the agent of head smut, were maintained in culture up to the regeneration of healthy plantlets. Production of plants remained low and depended on a synchronization of the date of inoculation with the physiological condition of the mother-plant, which is linked to the season. Use of fungicide throughout the experiment prevented the colonization by the parasite. Such a regeneration takes advantage of a vegetative reversal naturally induced by S. reilianum on certain spikelets. Our method produced regenerants whose characters are different from those of mother-plant: the panicle was always replaced by a fertile ear. This revised version was published online in June 2006 with corrections to the Cover Date.     

Partial reversion at the bobbed locus of Drosophila melanogaster

In Drosophila melanogaster the tandemly arranged repetitive sequences coding for 18S and 28S rRNA are heterogenous at the level of the spacers between units and insertions that interrupt many 28S rRNA genes. This heterogeneity contrasts with the homogeneity of the regions transcribed into 18S and 28S rRNA. Homogenization and evolution of repetitive genes are usually explained by conversion, amplification events or unequal crossovers. In this paper we studied the change in rDNA patterns associated with partial reversion of bobbed mutations. In most cases, no increase in rDNA gene number, but a new repartition of gene types were found.     

Color reversion of the albino medaka fish associated with spontaneous somatic excision of the Tol‐1 transposable element from the tyrosinase gene

The medaka fish albino mutant, i¹ is one of the Tomita collection of medaka pigmentation mutants which exhibits a complete albino phenotype, because of inactivation of the tyrosinase gene due to insertion of a transposable element, Tol‐1. Recently, mosaic black‐pigmented i¹ medaka fish have arisen in one of our laboratory breeding populations. Their pigmented cells have been observed in all of the tissues, including the eye and skin, in which melanin is detectable in the wild type. In this study, we analyzed the tyrosinase gene of revertants and showed Tol‐1 to have been precisely excised from the gene, suggesting a causal relationship. Mosaic patterns of pigmentation indicate spontaneous somatic excision of the element from the tyrosinase gene. To our knowledge, this is the first transposable element with somatic excision activity demonstrated phenotypically in vertebrates. The pattern of pigmentation in mosaic revertants indicates frequencies of melanin pigments to be consistent with the numbers of melanophores per unit area of body sites, such as the eyes, head and dorsal trunk.     

乌兰布和沙漠中国沙棘果实成熟期茎干液流规律及其与环境因子的关系

利用TDP液流测量系统和自动气象站对乌兰布和沙漠中国沙棘(Hippophae rhamnoides L.subsp.sinensis Rousi)的液流变化及其环境因子进行观测。结果表明:沙棘的茎干液流速率呈"几"字宽峰曲线,昼夜变化明显,夜间仍有低值液流;液流启动时间为8:00,在10:00左右达到峰值,峰值大小为227.94~307.86 g·h-1,至21:30基本下降到了极低值(11.04~26.29 g·h-1)。沙棘液流速率变化趋势与环境因子变化趋势相吻合。晴天液流速率较大,变化幅度也大,变幅在300 g·h-1以上;阴雨天液流速率变化小。相关性分析表明,影响沙棘液流速率的主要因子为太阳总辐射、空气相对湿度、空气温度以及风速。另外,沙棘液流与蒸腾速率日变化曲线均为单峰曲线,但叶片蒸腾速率峰值出现时间滞后液流峰值出现时间3 h。     

Fast drug rotation reduces bacterial resistance evolution in a microcosm experiment

Drug rotation (cycling), in which multiple drugs are administrated alternatively, has the potential for limiting resistance evolution in pathogens. The frequency of drug alternation could be a major factor to determine the effectiveness of drug rotation. Drug rotation practices often have low frequency of drug alternation, with an expectation of resistance reversion. Here we, based on evolutionary rescue and compensatory evolution theories, suggest that fast drug rotation can limit resistance evolution in the first place. This is because fast drug rotation would give little time for the evolutionarily rescued populations to recover in population size and genetic diversity, and thus decrease the chance of future evolutionary rescue under alternate environmental stresses. We experimentally tested this hypothesis using the bacterium Pseudomonas fluorescens and two antibiotics (chloramphenicol and rifampin). Increasing drug rotation frequency reduced the chance of evolutionary rescue, and most of the finally surviving bacterial populations were resistant to both drugs. Drug resistance incurred significant fitness costs, which did not differ among the drug treatment histories. A link between population sizes during the early stages of drug treatment and the end-point fates of populations (extinction vs survival) suggested that population size recovery and compensatory evolution before drug shift increase the chance of population survival. Our results therefore advocate fast drug rotation as a promising approach to reduce bacterial resistance evolution, which in particular could be a substitute for drug combination when the latter has safety risks.