Phylogenetic relationships among transposon-like elements in human and primate DNA

A THE-1 sequence in intron 7 of the human dystrophin gene has been found to represent a new subfamily of THE-1 elements. The sequence is closely related to the MstII family of repetitive sequences and is more like single-copy sequences found in the galago genome than any other THE-1 sequence previously reported. This new THE-1 sequence has been compared with two other complete THE-1 sequences and three related long-terminal repeat elements that we have previously found in intron 7 of the dystrophin gene, and with members of the same family from elsewhere in the primate genome. Parsimony and deletion analysis show that the cluster of THE-1 sequences in intron 7 of the dystrophin gene has arisen from at least three individual insertion events, rather than from the insertion and duplication of a single progenitor sequence. Correspondence to: G.B. Petersen     

Developmental and pathogen-induced activation of an msr gene, str246C, from tobacco involves multiple regulatory elements

A family of genes, the so-called msr genes (multiple stimulus response), has recently been identified on the basis of sequence homology in various plant species. Members of this gene family are thought to be regulated by a number of environmental or developmental stimuli, although it is not known whether any one member responds more specifically to one stimulus, or whether each gene member responds to various environmental stimuli. In this report, we address this question by studying the tobacco msr gene str246C. Using transgenic tobacco plants containing 2.1 kb of 5 flanking DNA sequence from the str246C gene fused to the -glucuronidase (GUS) coding region, the complex expression pattern of the str246C promoter has been characterized. Expression of the str246C promoter is strongly and rapidly induced by bacterial, fungal and viral infection and this induction is systemic. Elicitor preparations from phytopathogenic bacteria and fungi activate the str246C promoter to high levels, as do wounding, the application of auxin, auxin and cytokinin, salicylic acid or copper sulfate, indicating the absence of gene specialization within the msr gene family, at least for str246C. In addition, GUS activity was visualized. histochemically in root meristematic tissues of tobacco seedlings and is restricted to roots and sepals of mature plants. Finally, analysis of a series of 5 deletions of the str246C promoter-GUS gene fusion in transgenic tobacco plants confirms the involvement of multiple regulatory elements. A region of 83 by was found to be necessary for induction of promoter activity in response to Pseudomonas solanacearum, while auxin inducibility and root expression are apparently not controlled by this element, since its removal does not abolish either response. An element of the promoter with a negative effect on promoter activation by P. solanacearum was also identified.Joint first authors     

Maintenance of transposable element copy number in natural populations of Drosophila melanogaster and D. simulans

To investigate the main forces controlling the containment of transposable elements (TE) in natural populations, we analyzed the copia, mdg1, and 412 elements in various populations of Drosophila melanogaster and D. simulans. A lower proportion of insertion sites on the X chromosome in comparison with the autosomes suggests that selection against the detrimental effects of TE insertions is the major force containing TE copies in populations of Drosophila. This selection effect hypothesis is strengthened by the absence of the negative correlation between recombination rate and TE copy number along the chromosomes, which was expected under the alternative ectopic exchange model (selection against the deleterious rearrangements promoted by recombination between TE insertions). A cline in 412 copy number in relation to latitude was observed among the natural populations of D. simulans, with very high numbers existing in some local populations (around 60 copies in a sample from Canberra, Australia). An apparent absence of selection effects in this Canberra sample and a value of transposition rate equal to 1–2 × 10^-3 whatever the population and its copy number agree with the idea of recent but temporarily drastic TE movements in local populations. The high values of transposition rate in D. simulans clearly disfavor the hypothesis that the low amount of transposable elements in this species could result from a low transposition rate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Distribution of transposable elements in neotropical species of Drosophila

The phylogenetic distribution of transposable families, P, gypsy, hobo, I, and mariner has been analyzed in 33 species of 11 groups of neotropical Drosophila and a Drosophilidae species Zygotrica vittimaculosa, using squash blot and dot blot. Genomic DNA of almost all neotropical species tested hybridized with gypsy probe and some species showed a particularly strong hybridization signal, as D. gaucha, D. virilis, and species of flavopilosa group. The hobo element was restricted to melanogaster group and some strains of D. willistoni. Only D. simulans DNA showed hybridization to mariner probe in all species tested and D. simulans and D. melanogaster showed hybridization with I element probe. P element homologous sequence was present in D. melanogaster and all species and strains of the willistoni and saltans groups tested. The presence of at least one P-homologous sequence was detected in Drosophila mediopunctata. This one was the only P-bearing species of all six tested from the tripunctata group. Four different pairs of primers homologous to segments of the canonical sequence of D. melanogaster's P were used to amplify specific sequences from D. mediopunctata DNA, showing the occurrence of seemingly well-conserved P-homologous sequences. This revised version was published online in July 2006 with corrections to the Cover Date.     

Intragenomic distribution and stability of transposable elements in euchromatin and heterochromatin of drosophila melanogaster: non-LTR retrotransposon

The intragenomic location of the elements of the I, G, jockey, F, and Doc transposon families has been studied by the Southern blot analysis, in 12 laboratory Drosophila melanogaster stocks. Elements located in euchromatin, heterochromatin, and on the Y chromosome are identified, and their stability has been assessed by comparing the autoradiographs detected in different stocks and analysis of individual flies. Evidence is shown suggesting that preferential location in euchromatin or heterochromatin and the distribution within heterochromatin are distinctive of transposon families. Elements located in heterochromatin can be unstable. These results are discussed in the context of the relationship between transposable elements and the host genome. Received: 21 August 1996 / Accepted: 24 March 1997     

Sequences and Evolution of Human and Squirrel Monkey Blue Opsin Genes

The sequences of the entire blue opsin gene in the squirrel monkey (Saimiri boliviensis) and the five introns of the human blue opsin gene were obtained. Intron 3 of these genes contains an Alu sequence and intron 4 contains a partial mer13 sequence. A comparison of the squirrel monkey opsin sequence with published mammalian opsin sequences shows that features believed to be functionally critical are all conserved. However, the blue opsin has evolved twice as fast as rhodopsin and is only as conservative as the β globin, which has evolved at the average rate of mammalian proteins. Interestingly, the interhelical loops are, on average, actually more conservative than the transmembrane α helical regions. The introns of the blue opsin gene have evolved at the average rate of introns in primate genes. Received: 5 August 1996 / Accepted: 2 October 1996     

Interaction of Co,Mn, Mg and Al with d(GCGTACGC): a spectroscopic study

Spectroscopic study on the interactions of trace elements Co, Mn, Mg and Al with d(GCGTACGC) indicated the following: Al and Mg did not alter T_m values. Mn enhanced T_m at lower concentration and decreased it at higher concentrations. Interestingly Co at higher concentration elevated the T_m. These studies also showed lower concentrations of Mn displaced EtBr, whereas Al could displace it at higher ionic strength. Mg and Co displaced EtBr fluorescence at moderate concentrations. The binding constant values and CD spectra clearly indicated strong binding of these elements to DNA.     

南岭植物区系地理学研究──Ⅲ．植物区系地理亲缘与区划

南岭山地与相邻地区植物区系具有明显的过渡或替代关系,主要通过亚热带及亚热带亚热带亚洲分布成分与华南南亚热带及亚洲热带地区联系;与华中和华东地区植物区系的联系以亚热带及亚热带至温带分布和中国—日本间断分布成分来沟通;与西南地区植物区系的联系则表现为两地共有的古老和与遗成分区及石灰岩山地区系成分．华夏植物区系,是从古老的华夏植物群逐步发展起来的统一体,在区系分区上应划归为统一的华夏植物界,下分东亚植物区、马来西亚植物区和印度—喜马拉雅植物区。南岭山地植物区系拥有其自身的标志种、特有属和丰富的特有种,在区系分区上可划为完整的南岭植物亚省,下分东南岭植物县、中南岭植物县和西南岭植物县。     

The presence of extended phragmosomes containing cytoskeletal elements in fusiform cambial cells ofFraxinus excelsior L.

Summary Fusiform cambial cells of the ash (Fraxinus excelsior L.), which are strongly elongated and vacuolated, contain a phragmosome which traverses the whole length of the cells during preprophase and karyokinesis and which remains present during cytokinesis until it is integrated in cell plate with adjacent cytoplasm.The phragmosome consists of a thin perforated cytoplasmic layer located in the plane of the future cell plate. Otherwise oriented transvacuolar cytoplasmic layers or strands are not present in these cells.The phragmosome contains cytoskeletal elements, namely microtubules and also microfilament bundles both of which are oriented mainly in longitudinal direction.The phragmosomal microtubules are a new category of microtubules associated with cell division; presumably they guide the centrifugally growing cell plate to the parental cell wall site previously marked by the preprophase band of microtubules.