Phylogenetics of archerfishes (Toxotidae) and evolution of the toxotid shooting apparatus

Archerfishes (Toxotidae) are variously found in the fresh- and brackish-water environments of Asia Pacific and are well known for their ability to shoot water at terrestrial prey. These shots of water are intended to strike their prey and cause it to fall into the water for capture and consumption. While this behavior is well known, there are competing hypotheses (blowpipe vs. pressure tank hypothesis) of how archerfishes shoot and which oral structures are involved. Current understanding of archerfish shooting structures is largely based on two species, Toxotes chatareus and T. jaculatrix. We do not know if all archerfishes possess the same oral structures to shoot water, if anatomical variation is present within these oral structures, or how these features have evolved. Additionally, there is little information on the evolution of the Toxotidae as a whole, with all previous systematic works focusing on the interrelationships of the family. We first investigate the limits of archerfish species using new and previously published genetic data. Our analyses highlight that the current taxonomy of archerfishes does not conform to the relationships we recover. Toxotes mekongensis and T. siamensis are placed in synonymy of T. chatareus, Toxotes carpentariensis is recognized as a species and removed from synonymy of T. chatareus, and the genus Protoxotes is recognized for T. lorentzi based on the results of our analyses. We then take an integrative approach, using a combined analysis of discrete hard- and soft-tissue morphological characters with genetic data, to construct a phylogeny of the Toxotidae. Using the resulting phylogenetic hypothesis, we then characterize the evolutionary history and anatomical variation within the archerfishes. We discuss the variation in the oral structures and the evolution of the mechanism with respect to the interrelationships of archerfishes, and find that the oral structures of archerfishes support the blowpipe hypothesis but soft-tissue oral structures may also play a role in shooting. Finally, by comparing the morphology of archerfishes to their sister group, we find that the Leptobramidae has relevant shooting features in the oral cavity, suggesting that some components of the archerfish shooting mechanism are examples of co-opted or exapted traits.

Use of the Miniscreen assay to screen novel compounds for bacterial mutagenicity in the pharmaceutical industry

In vitro assays for mutagenicity are an important feature of pre-clinical testing and form part of the current regulatory testing conducted early in drug development. They can also play a part in compound selection since mutagenic compounds can be eliminated from a range of potential candidates. Bacterial tests are particularly useful in this area because they generate results quickly, though their use may be limited because they can require up to 4 g of material. A scaled-down version of the Ames test has been developed which requires only approximately 20 mg of material. Initial experiences with this assay using a range of known mutagens and novel compounds have shown that the Miniscreen has similar sensitivity to the Ames test. The major exception is for those mutagens preferentially detected with strains TA1537 and TA1535, which, because of their low spontaneous counts, are not employed in the Miniscreen.

Evaluation of pyrazole and ethanol induced S9 fraction in bacterial mutagenicity testing

A major constitutive enzyme in the liver of the uninduced rat is cytochrome P450-2E1. This isozyme has been shown to metabolize a number of carcinogens, including low molecular weight nitrosamines and a number of compounds normally regarded as non-mutagenic in the Ames test, e.g. aniline, urethane and benzene. Using the standard induction procedures [Aroclor 1254 or a combination of phenobarbitone (PB) and beta-naphthoflavone (beta-NF)] the level of CYP2E1 in rat liver is actually suppressed and it has been suggested that this may account for the negative findings with these compounds in the Ames test. S9 fractions were prepared from rats pre-treated with pyrazole or ethanol (inducers of CYP2E1) and then used in the Ames test (or pre-incubation modification) with urethane, acetaminophen, aniline, benzene, procarbazine and N-nitrosopyrrolidine. Both pyrazole and ethanol induced S9 were superior to PB/beta-NF-S9 and uninduced-S9 for the activation of N-nitrosopyrrolidine, a known CYP2E1 substrate. However, there was no evidence of mutagenic activity with urethane, aniline, benzene, procarbazine or acetaminophen. As these compounds have demonstrated genotoxicity in vivo, additional important metabolic pathways must be required which are not present in rat liver S9 fraction.

Report of the Association of British Pharmaceutical Industries Collaborative Study Group. Collaborative study to evaluate the inter/intra laboratory reproducibility and phenotypic stability of Salmonella typhimurium TA97a and TA102

A collaborative trial was carried out to determine the intra/interlaboratory variability of Salmonella typhimurium strains TA102 and TA97a with regard to spontaneous revertant frequency and in response to four model mutagens (cumene hydroperoxide and bleomycin for strain TA102, and 4-nitrophenylenediamine and 4-aminoantipyrine for strain TA97a). A secondary objective of the trial was to monitor the stability of the strains after storage for up to 8 months and identify any technical problems associated with their use. Thirteen different laboratories participated in the trial, all receiving identical stock cultures of the bacterial strains and samples from the same batch of mutagenic compound. A standard protocol was followed and two independent experiments were carried out within 1 month of receipt of the strains/compounds (phase I), and again after a period of 6-8 months (phase II). Comparative studies with the standard strain TA100 after treatment with 4-nitrophenylenediamine were carried out as part of phase II. Overall, both strains gave acceptably consistent results in different laboratories and are considered useful for screening purposes when used under standardized conditions. One major source of interlaboratory variability identified for TA102 appears to be the sensitivity of different types of automatic colony counter for detecting the micro-colony revertants that this strain produces.

Sensitivity of Salmonella typhimurium TA97a to the type of agar used for preparation of Vogel-Bonner plates

Recent problems with the supply of Difco bacto agar have forced some laboratories to evaluate alternative agars for use in the Salmonella/microsome assay. This led to the independent observation in two laboratories (Boots and Glaxo) that Salmonella typhimurium TA97a is sensitive to certain types of agar that may be used to prepare Vogel-Bonner minimal medium plates. A programme of work was, therefore, undertaken to investigate this phenomenon; 9-aminoacridine hydrochloride (at Boots) and 4-nitro-o-phenylenediamine (at Glaxo) were tested against TA1537 and TA97a using Vogel-Bonner plates prepared with a number of different agars. Three agars (Lab M, Difco Bi-tek and Beckton Dickinson granulated) were identified which, although supporting normal growth of TA1537 revertant colonies, gave much reduced control counts and responses to the mutagens with TA97a. One agar, Becton Dickinson grade A, gave poor responses with TA1537 but produced satisfactory results with TA97a. In contrast to the Vogel-Bonner plates, varying the type of agar used in the top agar overlays had little effect on the responses obtained. On the basis of these comparisons, Becton Dickinson purified agar was selected as a suitable alternative to Difco bacto and it was concluded that laboratories using agars other than these, or purchasing pre-poured plates without specifying the type of agar, should be made aware of potential problems with TA97a.

Comparison of Salmonella typhimurium TA102 with Escherichia coli WP2 tester strains

In 1982, Levin et al. published a paper describing a new Salmonella typhimurium strain, TA102, for detecting mutagenic agents that react preferentially with AT base pairs. This strain has an AT base pair at the critical mutation site within the hisG gene, which is located on a multicopy plasmid, pAQ1; the chromosomal copy of the hisG gene has been deleted. It also has an intact excision repair system, thus facilitating the detection of cross-linking agents, and carries the mutator plasmid, pKM101. Although TA102 has been shown to be reverted by certain mutagenic agents that are not detected in the usual battery of strains (TA1535, TA1537, TA1538, TA98 and TA100), there has been a general reluctance within the field to include TA102 as one of the standard screening strains. This may in part result from the difficulties which have been experienced in many laboratories in maintaining the strain, and in obtaining reproducible spontaneous and induced revertant counts. At Glaxo we routinely include certain Escherichia coli strains in our microbial test battery, and were aware that some of the genetic features offered by TA102 were already being covered by these strains. For example, E.coli WP2 (pKM101) has an AT base pair at the critical mutation site within the trpE gene, is excision proficient (and thus will detect cross-linking agents) and carries the pKM101 plasmid to enhance error-prone repair. From the published literature it was apparent that a number of the 'TA102 specific' mutagens could be detected in E.coli e.g. neocarzinostatin, UV and 8-MOP plus UV.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigations into the genotoxic potential of loxtidine, a long-acting H2-receptor antagonist

Loxtidine, a potent, non-competitive histamine H2-receptor antagonist was evaluated for genotoxic potential using a range of short-term mutagenicity assays. Unequivocally negative results were obtained in a Salmonella/plate incorporation assay and a liquid pre-incubation assay (using S. typhimurium strains TA1535, TA100, TA1537, TA1538 and TA98), a fluctuation assay [using Escherichia coli strains WP2, WP2 uvrA (R46) and 343/113 lys60 (R46)], a gene conversion assay (using Saccharomyces cerevisiae JD1) and a human peripheral lymphocyte cytogenetic assay. All of these in vitro tests were carried out in the presence and absence of rat liver S9 mix. In addition, the major metabolites of loxtidine in the rat were also negative in the same range of microbial mutagenicity assays. Loxtidine was inactive in the mouse micronucleus test after oral administration. The potential nitrosatability of loxtidine was investigated using an expanded version of the WHO Nitrosation Assay Procedure, and detectable quantities of mutagenic nitroso-species were not formed. The subsequent appearance of carcinoid tumours within the gastric fundus of rodents treated orally with loxtidine for most of their natural lifespan, led to additional assays being carried out on this compound to determine whether the tumorigenic effects were due to alternative mutagenic mechanisms. Negative results were obtained in an in vitro unscheduled DNA synthesis assay using primary rat hepatocytes, and an assay for spindle damaging agents using Muntjac skin fibroblasts. It can be concluded from these results that loxtidine is unlikely to be a genotoxic carcinogen. The increase in carcinoid tumour incidence observed in rats and mice after loxtidine treatment was probably related to the prolonged achlorhydria produced by this potent unsurmountable histamine H2-receptor antagonist.

The differential mutagenicity of isoniazid in fluctuation assays and Salmonella plate tests

The anti-tuberculostatic drug, isoniazid (INH) was evaluated for its mutagenic potential using Salmonella plate tests and fluctuation assays with various strains of bacteria, and different metabolic activation systems. In the Salmonella plate test INH proved to be a weak directly-acting base-substitution mutagen which was detoxified by S9-mix. S. typhimurium TA 1530 and TA 1535 were the sensitive strains, and this result confirmed some of the published data. In the present studies mutagenic activity was further diminished in the presence of larger concentrations of rat liver S9-mix. Furthermore, the reduction in mutagenic activity was observed with S9-mix derived from untreated, Aroclor 1254-treated or phenobarbitone/beta-naphthoflavone treated rats. In direct contrast, using the microtitre fluctuation assay, the mutagenic activity of INH was elevated in the presence of rat liver S9-mix, and continued to increase with increasing S9-concentration. This result was obtained irrespective of the S9-source. S. typhimurium strains TA 1530, TA 1535 and his G46, and E. coli strains TA 85, TA 86 and WP2 uvrA were all sensitive to the mutagenicity of INH after metabolic activation. The primary step in the metabolic activation of INH in the fluctuation test was mediated by a cytosolic enzyme, and the activity of dapsone as a competitive substrate implicated the involvement of an N-acetyl transferase. The rapid diffusion of the cytosolic enzyme into the basal agar layer, or the non-specific binding of the enzyme (or the active mutagenic INH metabolite) to components of the agar, may explain the contradictory data obtained in the Salmonella plate test. The modifying effects of agar on the distribution of drug metabolising enzymes within liver S9 fractions should be carefully considered when evaluating data from Salmonella plate tests.