A non-invasive micronucleus assay in the rat liver

The potent rat-liver mitogen 4-acetylaminofluorene (4AAF) is shown here to provide an effective replacement for the surgical procedure of 2/3 partial hepatectomy (2/3PH) in the in vivo rat-liver micronucleus assay described by Tates and his colleagues. This protocol modification enables the assay to be conducted on a routine basis. Control observations for both 2/3PH and 4AAF-treated rats are presented, together with evidence indicating 4AAF itself to be without activity in the assay, irrespective of the mitogenic stimulus. The activities of the rat carcinogens DMN, 2AAF, DMH and 6BT, and of the non-carcinogens 4AAF and 4N are demonstrated. Recommendations for the conduct of the modified assay are made.     

The function of mucous secretions in the cushion star Pteraster tesselatus Ives

In all previous studies involving the behavior of the cushion star Pteraster tesselatus Ives, the possibility that this asteroid's copious secretions of mucus are defensive in nature has been suggested, but never studied to any degree.

Our research shows that discharge of mucus from Pteraster was triggered not only by physical stimulation, but also from contact with the asteroid-consuming sea stars Solaster dawsoni Verrill and Pycnopodia helianthoides (Brandt). It was also found that mucus repelled these two asteroids so effectively that it provided Pteraster tesselatus with protection from predation for essentially 100% of the time.

Pteraster specimens were easily and harmlessly rendered defenseless by removing their mucous-cell-containing supradorsal membranes by dissection. Without the mucous secretions available for discharge, it was shown that P. tesselatus was easily preyed upon by both Solaster dawsoni and Pycnopodia helianthoides.     

Alterations to controls of cellular DNA synthesis by adenovirus infection.

Human adenovirus type 5 and temperature-sensitive mutants ts36, ts37, and ts125 induced cellular DNA synthesis in quiescent rodent cells at both permissive and nonpermissive temperatures. Cellular DNA synthesis induced by adenovirus type 5 or by serum required protein synthesis for both initiation and continuation, whereas viral DNA synthesis was not dependent upon continued protein synthesis once it was initiated. Both cellular and viral DNA replication was induced in adenovirus type 5-infected cells in the presence of dibutyryl cyclic AMP at concentrations which inhibited induction by serum which suggested that some of the controls of DNA synthesis in serum-treated and virus-infected cells are different. After adenovirus infection of quiescent cells, there was a decrease in the number of cells with G1 DNA content and an increase in cells with G2 diploid and greater DNA contents. Thus, adenovirus type 5 induces a complete round of cellular DNA replication, but in some cells, it induces a second round without completion of a normal mitosis. These results suggest that adenovirus type 5 is able to alter cell growth cycle controls in a way which may be related to its ability to transform cells.     

A sonar fish counter

The basic principles of a new technique for counting fish moving up or down stream are given. The counter is based on the ability to detect the presence of fish in an acoustic beam directed across the river. The counter is capable of counting several fish moving up or down stream simultaneously and is designed for use in wide open channels. The results of field trials with the equipment at two different sites are discussed together with the problems encountered. The results obtained are in good agreement with other methods of counting fish but the totals obtained were insufficient to put confidence limits on the counter.     

Gypsum and halite associated with the cyanobacterium Entophysalis

A study has been made on stalactite‐like structures formed by the cyanobacterium (blue‐green alga) En‐tophysalis major, growing on the roof of an undercut cliff facing the lagoon of Aldabra Atoll. The cyanobacterial cells grow in a rubbery, brown, gelatinous mucilage that contains some crystals; this mucilage surrounds a central region filled partly with gas and partly with further crystals. Halite is the predominant mineral in the mucilage, and gypsum the only mineral in the inner region. There is no evidence for a direct causal relationship between cyanobacterial metabolism and mineral crystallization, but the organic mucilage may have exerted an indirect physical control. A theory is suggested to explain the deposition of gypsum and halite, which depends on loss of water from the surface of the mucilage layer, and the layer as a whole acting as a semipermeable membrane. As the water volume decreases, gypsum will be deposited first, but subsequently, with increasing evaporation, there will be a mixture of gypsum and halite and finally halite only.     

Environmental enrichment promotes neural plasticity and cognitive ability in fish

Different kinds of experience during early life can play a significant role in the development of an animal''s behavioural phenotype. In natural contexts, this influences behaviours from anti-predator responses to navigation abilities. By contrast, for animals reared in captive environments, the homogeneous nature of their experience tends to reduce behavioural flexibility. Studies with cage-reared rodents indicate that captivity often compromises neural development and neural plasticity. Such neural and behavioural deficits can be problematic if captive-bred animals are being reared with the intention of releasing them as part of a conservation strategy. Over the last decade, there has been growing interest in the use of environmental enrichment to promote behavioural flexibility in animals that are bred for release. Here, we describe the positive effects of environmental enrichment on neural plasticity and cognition in juvenile Atlantic salmon (Salmo salar). Exposing fish to enriched conditions upregulated the forebrain expression of NeuroD1 mRNA and improved learning ability assessed in a spatial task. The addition of enrichment to the captive environment thus promotes neural and behavioural changes that are likely to promote behavioural flexibility and improve post-release survival.     

Mutagenesis of benzo[a]pyrene diol epoxide in yeast: requirement for DNA polymerase zeta and involvement of DNA polymerase eta

Benzo[a]pyrene is a potent environmental carcinogen, which can be metabolized in cells to the DNA damaging agent anti-benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (anti-BPDE). We hypothesize that mutations induced by BPDE DNA adducts are mainly generated through an error-prone translesion synthesis that requires a specialized DNA polymerase (Pol). Using an in vivo mutagenesis assay in the yeast model system, we have examined the potential roles of Pol(zeta) and Pol(eta) in (+/-)-anti-BPDE-induced mutagenesis. In cells proficient in mutagenesis, (+/-)-anti-BPDE induced 85% base substitutions with predominant G --> C followed by G --> T transversions, 9% deletions of 1-3 nucleotides, and 6% insertions of 1-3 nucleotides. In rad30 mutant cells lacking Pol(eta), (+/-)-anti-BPDE-induced mutagenesis was reduced and accompanied by a moderate decrease in base substitutions and more significant decrease in deletions and insertions of 1-3 nucleotides. In rev3 mutant cells lacking Pol(zeta), (+/-)-anti-BPDE-induced mutagenesis was mostly abolished, leading to a great decrease in both base substitutions and deletions/insertions of 1-3 nucleotides. In contrast, large deletions/insertions were significantly increased in cells lacking Pol(zeta). Consistent with the in vivo results, purified yeast Pol(zeta) performed limited translesion synthesis opposite (+)- and (-)-trans-anti-BPDE-N(2)-dG DNA adducts with predominant G incorporation opposite the lesion. These results show that (+/-)-anti-BPDE-induced mutagenesis in yeast requires Pol(zeta) and partially involves Pol(eta) and suggest that Pol(zeta) directly participates in nucleotide insertions opposite the lesion, while Pol(eta) significantly contributes to deletions and insertions of 1-3 nucleotides.