A molecular study of phylogenetic relationships and evolution of antipredator strategies in Australian Diplodactylus geckos, subgenus Strophurus

We present phylogenetic analyses of the lizard genus Diplodactylus subgenus Strophurus using 1646 aligned positions of mitochondrial DNA sequences containing 893 parsimony-informative characters for samples of 12 species of Strophurus and 19 additional Australian gecko species. Sequences from three protein-coding genes (ND1, ND2 and COI) and eight intervening transfer RNA genes were examined using parsimony, maximum-likelihood and Bayesian analyses. Species of Strophurus appeared to form a monophyletic group with the possible exception of S. taenicauda . Strophurus has evolved two distinct defence/display characteristics: caudal glands, which expel an unpalatable substance, and striking mouth colours. Caudal glands appeared to have arisen once in a common ancestor of Strophurus , with dermal augmentation of caudal glands characterizing a subclade within the subgenus. Evolution of yellow and dark-blue mouth colours in Strophurus occurred in the context of diurnal activity and may be interpreted as an augmentation of defensive behavioural displays. Molecular divergence suggests that arboreality evolved in a common ancestor of Oedura and Strophurus approximately 29 Mya and that the caudal glands of Strophurus arose approximately 25 Mya.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 123–138.     

Nonrandom location of IS1 elements in the genomes of natural isolates of Escherichia coli

We have studied the spatial distribution of IS1 elements in the genomes of natural isolates comprising the ECOR reference collection of Escherichia coli. We find evidence for nonrandomness at three levels. Many pairs of IS1 elements are in much closer proximity (< 10 kb) than can be accounted for by chance. IS1 elements in close proximity were identified by long-range PCR amplification of the genomic sequence between them. Each amplified region was sequenced and its map location determined by database screening of DNA hybridization. Among the ECOR strains with at least two IS1 elements, 54% had one or more pairs of elements separated by < 10 kb. We propose that this type of clustering is a result of "local hopping," in which we assume that a significant proportion of tranposition events leads to the insertion of a daughter IS element in the vicinity of the parental element. A second level of nonrandomness is found in strains with a modest number of IS1 elements that are mapped through the use of inverse PCR to amplify flanking genomic sequences: in these strains, the insertion sites tend to be clustered over a smaller region of chromosome than would be expected by chance. A third level of nonrandomness is observed in the composite distribution of IS elements across strains: among 20 mapped IS1 elements, none were found in the region of 48-77 minutes, a significant gap. One region of the E. coli chromosome, at 98 min, had a cluster of IS1 elements in seven ECOR strains of diverse phylogenetic origin. We deduce from sequence analysis that this pattern of distribution is a result of initial insertion in the most recent common ancestor of these strains and therefore not a hot spot of insertion. Analysis using long- range PCR with primers for IS2 and IS3 also yielded pairs of elements in close proximity, suggesting that these elements may also occasionally transpose by local hopping.      

Horizontal transmission, vertical inactivation, and stochastic loss of mariner-like transposable elements

Horizontal transmission has been well documented as a major mechanism for the dissemination of mariner-like elements (MLEs) among species. Less well understood are mechanisms that limit vertical transmission of MLEs resulting in the "spotty" or discontinuous distribution observed in closely related species. In this article we present evidence that the genome of the common ancestor of the melanogaster species subgroup of Drosophila contained an MLE related to the mellifera (honey bee) subfamily. Horizontal transmission, approximately 3-10 MYA, is strongly suggested by the observation that the sequence of the MLE in Drosophila erecta is 97% identical in nucleotide sequence with that of an MLE in the cat flea, Ctenocephalides felis. The D. erecta MLE has a spotty distribution among species in the melanogaster subgroup. The element has a high copy number in D. erecta and D. orena, a moderate copy number in D. teissieri and D. yakuba, and was apparently lost ("stochastic loss") in the lineage leading to D. melanogaster, D. simulans, D. mauritiana, and D. sechellia. In D. erecta, most copies are concentrated in the heterochromatin. Two copies from D. erecta, denoted De12 and De19, were cloned and sequenced, and they appear to be nonfunctional ("vertical inactivation"). It therefore appears that the predominant mode of MLE evolution is vertical inactivation and stochastic loss balanced against occasional reinvasion of lineages by horizontal transmission.      

Dynamic compression counteracts IL-1β induced inducible nitric oxide synthase and cyclo-oxygenase-2 expression in chondrocyte/agarose constructs

Background  

Nitric oxide and prostaglandin E₂ (PGE₂play pivotal roles in both the pathogenesis of osteoarthritis and catabolic processes in articular cartilage. These mediators are influenced by both IL-1β and mechanical loading, and involve alterations in the inducible nitric oxide synthase (iNOS) and cyclo-oxygenase (COX)-2 enzymes. To identify the specific interactions that are activated by both types of stimuli, we examined the effects of dynamic compression on levels of expression of iNOS and COX-2 and involvement of the p38 mitogen-activated protein kinase (MAPK) pathway.