The evolution of long interspersed repeated DNA (L1, LINE 1) as revealed by the analysis of an ancient rodent L1 DNA family

Summary All modern mammals contain a distinctive, highly repeated (⩾50,000 members) family of long interspersed repeated DNA called the L1 (LINE 1) family. While the modern L1 families were derived from a common ancestor that predated the mammalian radiation ∼80 million years ago, most of the members of these families were generated within the last 5 million years. However, recently we demonstrated that modern murine (Old World rats and mice) genomes share an older long interspersed repeated DNA family that we called Lx. Here we report our analysis of the DNA sequence of Lx family members and the relationship of this family to the modern L1 families in mouse and rat. The extent of DNA sequence divergence between Lx members indicates that the Lx amplification occurred about 12 million years ago, around the time of the murine radiation. Parsimony analysis revealed that Lx elements were ancestral to both the modern rat and mouse L1 families. However, we found that few if any of the evolutionary intermediates between the Lx and the modern L1 families were extensively amplified. Because the modern L1 families have evolved under selective pressure, the evolutionary intermediates must have been capable of replication. Therefore, replicationcompetent L1 elements can reside in genomes without undergoing extensive amplification. We discuss the bearing of our findings on the evolution of L1 DNA elements and the mammalian genome.     

ANTIVIRAL ACTIVITY OF CULTURED BLUE-GREEN ALGAE (CYANOPHYTA)1

Lipophilic and hydrophilic extracts from approximately 600 strains of cultured cyanophytes, representing some 300 species, were examined for antiviral activity against three pathogenic viruses. Approximately 10% of the cultures produced substances that caused significant reduction in cytopathic effect normally associated with viral infection. The screening program identified the order Chroococcales as commonly producing antiviral agents.     

ADrosophila homologue of theSchizosaccharomyces pombe act2 gene

Diverse proteins that are 35% to 55% identical to actins have been discovered recently in yeasts, nematodes, and vertebrates. In order to study these proteins systematically and relate their functions to those of conventional actins, we are isolating the corresponding genes from the genetically tractable eukaryote,Drosophila melanogaster. Here we report the isolation and partial characterization of aDrosophila homologue of theSchizosaccharomyces pombe act2 gene. Degenerate oligonucleotide primers specifying peptides that are highly conserved within the actin protein superfamily were used in conjunction with polymerase chain reaction (PCR) to amplify a portion of theDrosophila gene that we have namedactr66B. The corresponding full-length cDNA sequence encodes a protein of 418 residues that is 65% identical to the product of theS. pombe act2 gene, 80% identical to the bovineact2 homologue, but only 48% identical to the principalDrosophila cytoplasmic actin encoded by theAct5C actin gene. Alignment of the yeast, bovine, andDrosophila actin-related proteins shows that they have four peptide insertions, relative to conventional actins, three of which are well placed to modify actin polymerization and one that is likely to perturb the binding of myosin. Locations of two of the fiveactr66B introns are conserved betweenDrosophila and yeast genes, further attesting that they evolved from a common ancestor and are likely to encode proteins having similar functions. We demonstrate that theDrosophila gene is located on the left arm of chromosome 3, within subdivision 66B. Finally, we show by RNA blot-hybridization that the gene is expressed at low levels, relative to conventional nonmuscle actin, in all developmental stages. From these and other observations we infer that the actr66B protein is a minor component of all cells, perhaps serving to modify the polymerization, structure, and dynamic behavior of actin filaments. Our work was supported by grants from the NIH and the Muscular Dystrophy Association to E.A.F. Sequences described herein have been filed in the GenBank Database under Accession Number X71789.     

S-adenosyl-l-methionine inhibits phosphoinositide metabolism in the rat brain synaptosomal suspensions

S-adenosyl-l-methionine (AdoMet) has been reported to affect events linked to noradrenergic neurotransmission. In the present work, we studied the effect of AdoMet on norepinephrine (NE)-stimulated inositol phosphate production in³H-inositol-labelled crude synaptosomal suspensions of rat brain. AdoMet (50–1000 M) decreased both the synthesis of labelled polyphosphoinositide (30–50%) and the release of inositol mono- and bisphosphate (40–50%). The AdoMet effect was not dependent on NE concentration (10–1000 M), suggesting that the inhibition of inositol phosphate release was not the result of a modification of the norepinephrine binding to its receptor sites. S-adenosyl-L-homocysteine (AdoHcy) (1 mM) an inhibitor of methyltransferase activities, partially inhibited (70%) the AdoMet (0.1 mM) effect, indicating that the methylation processes cannot explain all the effects observed. We conclude that, in addition to previously reported effects of AdoMet on NE transport, AdoMet may reduce NE-linked intracellular signalling.     

Human reciprocal translocations: is the unbalanced mode at birth predictable?

Two methods of prediction for the risk of unbalance at birth were tested on a large data base of reciprocal translocation (1376 families): the pachyten diagram predictive method (PDPmethod) and the discriminant method (Dmethod). These method succeeded in correctly predicting the segregation mode in 66% of the data for the PDPmethod and in 80% of the data for the Dmethod. The quality of chromosome material (in particular R bands) must be taken into account for more accurate prediction. Some difficulties still exist in predicting the 31 tertiary segregation mode, which can frequently be incorrectly classified as the adjacent 1 mode.     

The ClpE protein involved in biogenesis of the CS31A capsule-like antigen is a member of a periplasmic chaperone family in Gram-negative bacteria

Abstract The putative chaperone-like protein ClpE, required for biogenesis of the Escherichia coli capsule-like antigen CS31A, was compared with ten known periplasmic chaperones from E. coli, Klebsiella pneumoniae, Bordetella pertussis, Haemophilus influenzae and Yersinia pestis . The amino acid sequence alignment was superimposed onto the three-dimensional structure of the PapD chaperone of uropathogenic E. coli , and amino acid residues involved in maintaining the structure integrity of the suggested binding site were found identical in most of the 11 chaperones. Construction of a phylogenetic tree to investigate the relationship within the chaperone family has revealed interesting degrees of relatedness between the different proteins.     

Deletion analysis of the essentiality of penicillin-binding proteins 1A, 2B and 2X of Streptococcus pneumoniae

Abstract An internal fragment from each of the penicillinebinding protein (PBP) 1A, 2B and 2X genes of Streptococcus pneumoniae , which included the region encoding the active-site serine residue, was replaced by a fragment encoding spectinomycin resistance. The resulting constructs were tested for their ability to transform S. pneumoniae strain R6 to spectinomycin resistance. Spectinomycin-resistant transformants could not be obtained using either the inactivated PBP 2X or 2B genes, suggesting that deletion of either of these genes was a lethal event, but they were readily obtained using the inactivated PBP 1A gene. Analysis using the polymerase chain reaction confirmed that the latter transformants had replaced their chromosomal copy of the PBP 1A gene with the inactivated copy of the gene. Deletion of the PBP 1A gene was therefore tolerated under laboratory conditions and appeared to have little effect on growth or susceptibility to benzylpenicillin.     

Two centuries of spatial and temporal dynamics of freshwater fish introductions

Aim

Investigating major freshwater fish flows (translocations) between biogeographic regions and their temporal dynamics and also quantifying spatial patterns and temporal changes in the array of introduced species, and the emergence and distance between major donor and recipient regions.

Location

Global.

Time Period

1800–2020.

Major Taxa Studied

Freshwater fishes.

Methods

We analysed a global dataset on freshwater fish introductions (4241 events of 688 species). Freshwater fish flows were investigated with flow diagrams and χ² tests, while PERMANOVA (permutational multivariate analysis of variance) was used to test the association between species and regions and temporal shifts. Cluster analysis revealed major recipient areas and composition of the introduced species. Finally, changes in distances between donor and recipient sites were tested with PERMANOVA.

Results

The number of introductions between biogeographic regions mirrored the European and North American dominance before World War II (WWII) and the trends in recreational fishing, biocontrol programmes and food production, especially in the Sino-Oriental region, which has a long tradition of aquaculture and fishkeeping. Over the years, the origins and composition of introduced species changed uniquely in each biogeographic region, although the most introduced species are common to every region. Salmonids and other cold-water species were frequently introduced before the 1950s, whereas tropical ornamental and aquaculture species currently prevail. Distances between donor and recipient sites did not vary over the time. After WWII, the Sino-Oriental region consolidated its dominance and the Ethiopian and Neotropical regions emerged as new global donor and recipient regions.

Main Conclusions

Global policy should focus on tropical ornamental and aquaculture species, which could benefit from global warming, especially in the Sino-Oriental region, because it currently dominates freshwater fish species flows, and the Ethiopian and Neotropical regions, because they recently emerged as important global donor and recipient regions of freshwater fish introductions.     

Induction of phagocytic behaviour in human epithelial cells by Escherichia coli cytotoxic necrotizing factor type1

Cytotoxic necrotizing factor type 1 (CNF1) from strains of pathogenic Escherichia coli induces in human epithelial HEp-2 cells, a profound reorganization of the actin cytoskeleton into prominent stress fibres and membrane ruffles. We report here that this process is associated with induction of phagocytic-like activity. CNF1-treated cells acquired the ability to ingest latex beads as well as non-invasive bacteria such as Listeria innocua, which were taken as a model system. Uptake of bacteria was similar to pathogen-induced phagocytosis, since L. innocua transformed with DNA coding for the pore-forming toxin listeriolysln O behaved, with respect to intracellular growth, like the invasive, pathogenic species L. monocytogenes. Our results raise the possibility that, in vivo, pathogenic CNF1 -producing E. coli may invade epithelia by this novel induced phagocytic-like mechanism.