Ring species as bridges between microevolution and speciation

A demonstration of how small changes can lead to species-level differences is provided by ring species, in which two reproductively isolated forms are connected by a chain of intermediate populations. We review proposed cases of ring species and the insights they provide into speciation. Ring species have been viewed both as illustrations of the history of divergence of two species from their common ancestor and as demonstrations that speciation can occur in spite of gene flow between the diverging forms. Theoretical models predict that speciation with gene flow can occur when there is divergent ecological selection, and geographical differentiation increases the likelihood of speciation. Thus ring species are ideal systems for research into the role of both ecological and geographical differentiation in speciation, but few examples have been studied in detail. The Greenish warbler is a ring species in which two northward expansions around the Tibetan plateau have been accompanied by parallel evolution in morphology, ecology, and song length and complexity. However, songs have diverged in structure, resulting in a lack of recognition where the reproductively isolated forms come into contact in Siberia. Our analysis suggests that these differences could have arisen even with gene flow, and that parallel rather than divergent ecological changes have led to divergence in sexually selected traits and subsequent speciation.     

Increased Expression of Several Mitochondrial Genes in Human and Monkey B-Cell Non-Hodgkin Lymphomas

Mitochondrial genes overexpressed in human and monkey B-cell non-Hodgkin lymphomas (B-NHLs) were sought via subtraction hybridization, cloning, and differential screening of the resulting cDNA libraries. The cDNAs of mitochondrial genes constituted an appreciable proportion of all lymphoma-specific cDNAs. Lymphomogenesis was associated with upregulation of a set of mitochondrial genes, which varied with lymphoma type but always included NADHIV. A possible association between upregulation of certain mitochondrial genes and cell malignant transformation is discussed.     

Mutagenesis and computer modelling approach to study determinants for recognition of signal peptides by the mitochondrial processing peptidase

Determinants for the recognition of a mitochondrial presequence by the mitochondrial processing peptidase (MPP) have been investigated using mutagenesis and bioinformatics approaches. All plant mitochondrial presequences with a cleavage site that was confirmed by experimental studies can be grouped into three classes. Two major classes contain an arginine residue at position -2 or -3, and the third class does not have any conserved arginines. Sequence logos revealed loosely conserved cleavage motifs for the first two classes but no significant amino acid conservation for the third class. Investigation of processing determinants for a class III precursor, Nicotiana plumbaginifolia F1beta precursor of ATP synthase (pF1beta), was performed using a series of pF1beta presequence mutants and mutant presequence peptides derived from the C-terminal portion of the presequence. Replacement of -2 Gln by Arg inhibited processing, whereas replacement of either the most proximally located -5 Arg or -15 Arg by Leu had only a low inhibitory effect. The C-terminal portion of the pF1beta presequence forms a helix-turn-helix structure. Mutations disturbing or prolonging the helical element upstream of the cleavage site inhibited processing significantly. Structural models of potato MPP and the C-terminal pF1beta presequence peptide were built by homology modelling and empirical conformational energy search methods, respectively. Molecular docking of the pF1beta presequence peptide to the MPP model suggested binding of the peptide to the negatively charged binding cleft formed by the alpha-MPP and beta-MPP subunits in close proximity to the H111XXE114H115X(116-190)E191 proteolytic active site on beta-MPP. Our results show for the first time that the amino acid at the -2 position, even if not an arginine, as well as structural properties of the C-terminal portion of the presequence are important determinants for the processing of a class III precursor by MPP.     

长江三峡库区及其邻近地区的残存稀有濒危植物群落

长江三峡库区及其邻近地区的残存稀有濒危植物群落属于中亚热带绿落叶阔叶混交林。群落所处自然环境少生境独特;群落中有数种至十余种稀有濒危植物群聚生长,且以其中的部分稀有濒危植物为优势种。独特的生增昨良好的群落结构被认为是该类群落得以保存的主要原因,应加强对该类群落的就地保护研究。     

人胃癌细胞一种高表达基因的克隆及序列测定

采用DDRT-PCR法,以人胃上皮细胞GES-1为对照,从人胃癌细胞SGC-7901中克隆高表达基因,并对所克隆的基因进行斑点杂交分析, 序列测定,序列相似性分析及开放读框分析.斑点杂交分析结果表明所获克隆YA61为人胃癌细胞SGC-7901中高表达基因.序列相似性分析结果表明该基因序列为一新基因序列.GenBank收录号为AF220415.开放读框分析结果表明该基因序列有一完全开放读框.     

Four members of the Sox gene family in channel catfish

The homologous sequences of human or mouse SOX1, SOX4 and SOX11 , and one novel Sox gene (named Ccf-SoxN ) were identified in the genome of channel catfish Ictalurus punctatus . Identification of these genes is a potential step in understanding development regulations including sex determination in channel catfish.     

Temperature impact on the midsummer decline of Daphnia galeata: an analysis of long-term data from the biomanipulated Bautzen Reservoir (Germany)

1. The influence of water temperature on occurrence and duration of a midsummer decline (MSD) of Daphnia galeata was studied in the biomanipulated Bautzen Reservoir in Germany. The proportion of piscivores in the fish community of the reservoir has been enhanced experimentally since 1981. As a consequence, Daphnia galeata has dominated the zooplankton. Over 18 years of study (1981–1998), a long‐lasting MSD (longer than 30 days) occurred in 7 years, whereas a short MSD (shorter than 30 days) was observed in 6 years. During the remaining 5 years, an MSD was not observed.
2. Two hypotheses were examined to explain the observed patterns. First, we postulated that high water temperature during winter and early spring (January–April) leads to an MSD after an early and high spring peak of daphnids. On the other hand, low temperature during winter and early spring should not cause an MSD owing to a slower increase of the population, resulting in a later peak of daphnids. Second, we hypothesized that the mean water temperature during early summer (May and June) influences the occurrence of an MSD (by controlling young‐of‐the‐year (YOY) fish predation on daphnids).
3. The water temperature during winter and early spring explains 83%, and the early summer water temperature 55%, of interannual variation in the occurrence of an MSD.
4. The interannual variation in duration of an MSD was neither explained by temperature during winter and early spring nor by early summer temperature alone, but in 14 of the 18 years (78%) by a combination of both.
5. We conclude that water temperature during winter and early spring had a strong impact on Daphnia mortality by influencing height and timing of the spring peak which, in turn, influenced the extent of overexploitation of their food resources. By contrast, the water temperature during early summer probably influenced the mortality of daphnids caused by predation of YOY fish. The relative timing of both sources of mortality, which depends on the temperature regime during the first 6 months of the year, is the key process in controlling the occurrence and duration of an MSD. A long‐lasting MSD, therefore, is likely in Bautzen Reservoir only if temperatures are high during winter and early spring, as well as during early summer.
6. As a consequence of climate warming, recent climate records reveal warming during winter, spring and early summer in middle Europe, rather than an increase in mean annual temperatures. If our findings and conclusions are related to this regional and temporal pattern of climate warming, an increasing frequency of years with a long‐lasting MSD and, consequently, a decreasing efficiency of biomanipulation can be predicted.     

中国大麦矮秆种质资源的基因分析——Ⅱ.矮秆基因的染色体定位

根据连锁遗传原理,利用全套染色体形态性状标记系,对２０份中国大麦矮秆种质资源的矮秆基因,进行了染色体定位。结果表明：１５份单基因矮秆中,有１份其矮秆基因与宽护颖基因Ｚ连锁,位于２（２Ｈ）染色体短臂上;１０份的矮秆基因与ｕｚ基因等位,由３（３Ｈ）长臂携带;４份的矮秆基因与钩芒基因Ｋ连锁,位于４（４Ｈ）长臂上。５份双基因矮秆中,有３份的矮秆基因分别位于２（２Ｈ）短臂和４（４Ｈ）长臂上;１份的矮秆基因各由其３（３Ｈ）和４（４Ｈ）长臂携带;其余１份的两对矮秆基因,１对与ｕｚ基因等位,由３（３Ｈ）长臂携带,另１对则与宽护颖基因ｗ连锁,位于２（２Ｈ）短臂之上。     

Construction of a reporter plasmid for screening in vivo promoter activity in Francisella tularensis

Francisella tularensis is a facultative intracellular bacterium that survives and multiplies inside macrophages. Here we constructed a new promoter probe plasmid denoted pKK214 by introduction of a promoter-less chloramphenicol acetyltransferase (cat) gene into the shuttle vector pKK202. A promoter library was created in F. tularensis strain LVS by cloning random chromosomal DNA fragments into pKK214. Approximately 15% of the recombinant bacteria showed chloramphenicol resistance in vitro. The promoter library was also used to infect macrophages in the presence of chloramphenicol and after two cycles of infection the library contained essentially only chloramphenicol resistance clones which shows that pKK214 can be used to monitor F. tularensis genes that are expressed during infection.     

Protein kinase and phosphatase responses to anoxia in crayfish, Orconectes virilis: purification and characterization of cAMP-dependent protein kinase

The freshwater crayfish, Orconectes virilis, shows good anoxia tolerance, enduring 20 h in N₂-bubbled water at 15°C. Metabolic responses to anoxia by tolerant species often include reversible phosphorylation control over selected enzymes. To analyze the role of serine/threonine kinases and phosphatases in signal transduction during anoxia in O. virilis, changes in the activities of cAMP-dependent protein kinase (PKA) and protein phosphatases 1, 2A, and 2C were measured in tail muscle and hepatopancreas over a time course of exposure to N₂-bubbled water. A strong increase in the percentage of PKA present as the free catalytic subunit (% PKAc) occurred between 1 and 2 h of anoxia exposure whereas phosphatase activities were strongly reduced. This suggests that PKA-mediated events are important in the initial response by tissues to declining oxygen availability. As oxygen deprivation became severe and prolonged (5–20 h) these changes reversed; the % PKAc fell to below control values and activities of phosphatases returned to or rose above control values. Subcellular fractionation also showed a decrease in PKA associated with the plasma membrane after 20 h anoxia whereas cytosolic PKA content increased. PKAc purified from tail muscle showed a molecular weight of 43.8±0.4 kDa, a pH optimum of 6.8, a high affinity for Mg ATP (K_m=131.0±14.4 μM) and Kemptide (K_m=31.6±5.2 μM). Crayfish PKAc was sensitive to temperature change; a break in the Arrhenius plot occurred at approximately 15°C with a 2.5-fold rise in activation energy at temperatures <15°C. These studies demonstrate a role for serine/threonine protein kinases and phosphatases in the metabolic adjustments to oxygen depletion by crayfish organs.