Genome-wide identification and characterization of cytochrome P450 monooxygenase genes in the ciliate Tetrahymena thermophila

Background: Cytochrome P450 monooxygenases play key roles in the metabolism of a wide variety of substrates and they are closely associated with endocellular physiological processes or detoxification metabolism under environmental exposure. To date, however, none has been systematically characterized in the phylum Ciliophora. T. thermophila possess many advantages as a eukaryotic model organism and it exhibits rapid and sensitive responses to xenobiotics, making it an ideal model system to study the evolutionary and functional diversity of the P450 monooxygenase gene family. Results: A total of 44 putative functional cytochrome P450 genes were identified and could be classified into 13 families and 21 sub-families according to standard nomenclature. The characteristics of both the conserved intron-exon organization and scaffold localization of tandem repeats within each P450 family clade suggested that the enlargement of T. thermophila P450 families probably resulted from recent separate small duplication events. Gene expression patterns of all T. thermophila P450s during three important cell physiological stages (vegetative growth, starvation and conjugation) were analyzed based on EST and microarray data, and three main categories of expression patterns were postulated. Evolutionary analysis including codon usage preference, sit-especific selection and gene-expression evolution patterns were investigated and the results indicated remarkable divergences among the T. thermophila P450 genes. Conclusion: The characterization, expression and evolutionary analysis of T. thermophila P450 monooxygenase genes in the current study provides useful information for understanding the characteristics and diversities of the P450 genes in the Ciliophora, and provides the baseline for functional analyses of individual P450 isoforms in this model ciliate species.

五株纤毛虫遗传关系的ISSR分析

采用ISSR分子标记技术,尝试对四种五株纤毛虫(褶累枝虫(Epistylis plicatilis)、绿草履虫(Paramecium bursaria)、多态喇叭虫(Stentor polymorphus)、嗜热四膜虫BF1株(Tetrahymena thermophilaBF1)和嗜热四膜虫BF5株(T.ther-mophilaBF5))进行遗传关系研究。用13个ISSR引物对五株纤毛虫进行扩增,六个ISSR引物获得多态片段。根据Nei s遗传距离矩阵构建了五株纤毛虫的遗传关系树状图。UPGMA,NJ聚

Independent Transport and Sorting of Functionally Distinct Protein Families in Tetrahymena thermophila Dense Core Secretory Granules

Dense core granules (DCGs) in Tetrahymena thermophila contain two protein classes. Proteins in the first class, called granule lattice (Grl), coassemble to form a crystalline lattice within the granule lumen. Lattice expansion acts as a propulsive mechanism during DCG release, and Grl proteins are essential for efficient exocytosis. The second protein class, defined by a C-terminal beta/gamma-crystallin domain, is poorly understood. Here, we have analyzed the function and sorting of Grt1p (granule tip), which was previously identified as an abundant protein in this family. Cells lacking all copies of GRT1, together with the closely related GRT2, accumulate wild-type levels of docked DCGs. Unlike cells disrupted in any of the major GRL genes, Delta GRT1 Delta GRT2 cells show no defect in secretion, indicating that neither exocytic fusion nor core expansion depends on GRT1. These results suggest that Grl protein sorting to DCGs is independent of Grt proteins. Consistent with this, the granule core lattice in Delta GRT1 Delta GRT2 cells appears identical to that in wild-type cells by electron microscopy, and the only biochemical component visibly absent is Grt1p itself. Moreover, gel filtration showed that Grl and Grt proteins in cell homogenates exist in nonoverlapping complexes, and affinity-isolated Grt1p complexes do not contain Grl proteins. These data demonstrate that two major classes of proteins in Tetrahymena DCGs are likely to be independently transported during DCG biosynthesis and play distinct roles in granule function. The role of Grt1p may primarily be postexocytic; consistent with this idea, DCG contents from Delta GRT1 Delta GRT2 cells appear less adhesive than those from the wild type.

以营养动力学为基础的种间竞争模型的建立

本文从生物种群增长的营养动力学理论出发，建立了一个新的种间竞争的数学模型，这是单种群增长的崔-Iawson模型在种间竞争中的发展和推广。二者有着共同的比较真实可靠的理论基础。新的种间竞争模型在特殊条件下转化为经典的Lotka-Volterra竞争方程，二者有着相同的定性行为，但是，用作者提出的种群竞争力指数，新的种间竞争模型能够能够给予种间竞争结局一个符合生物、生态学原理的解，而且，新的种间竞争模型在定量行为上大大扩充了Lotka-Volterra竞争方程，例如，以非线性种内，种间竞争功能反应代替了Lotka-Volterra竞争方程线性种内、种间竞争功能反应。因此，新的种间竞争模型是对经典的Lotka-Volterra竞争方程的扩充。对Gause的原生Paramecium和caudatum Stylonychia mytilus种竞争实验的数据拟合表明，新的种间竞争模型与种间竞争实验结果达到非常好的吻合，相反，Lotka-Volterra竞争方程拟合效果很差。将新的种间竞争模型尝试性地应用于长白山北坡岳桦云冷杉林的优势树种的动态特性分析和预测，也得到良好的结果。本项研究弥补了生物种群增长的营养动力学研究在种间竞争方面的不足；克服了经典的Lotka-Volterra竞争方程及其他种间竞争模型的局限，发展和完善了种间竞争的理论；这对于促进生态学向成熟发展具有重要意义。