The biology of a giant dung-beetle (Heliocopris dilloni) (Coleoptera: Scarabaeidae)

Heliocopris dilloni is the largest dung-beetle found in the Tsavo National Park, Kenya, which during the biannual rainy seasons comprises the most important agency of elephant dung removal. The species is shown to exhibit considerable morphological variation. The mode of construction of the brood chamber is described together with details of development from egg to pupa. It is suggested that the depth to which these beetles burrow is related to avoiding the extreme climate near the surface and to predator avoidance.     

Oxidation of n-alkanes: Growth of Pseudomonas putida

Summary The induction of alkane hydroxylase activity was investigated in two strains of Pseudomonas putida with a view to the production of primary alcohols. n-Nonanol production rates (16.0 mol/g dry wt/h) with an alcohol dehydrogenase negative mutant P. putida PpS173 were considerably lower than might be expected from the growth of a wild type on n-alkane. Production of cells by fed-batch culture on n-nonane, with a specific alkane hydroxylase activity of 3.9 mmol/g/h, was considered most suitable for isolation of the alkane hydroxylase.     

Methylmercury: Effects on electrical properties of squid axon membranes

At low concentrations (25–100 μM) methylmercury chloride caused a steady increase in the threshold for excitation and on eventual block of action potentials without changing the resting membrane potential in squid giant axons. In the axons exposed to 25 μM methylmercury chloride, peak transient and steady-state conductances were decreased by 58.8 ± 5.1% and 35.9 ± 4.3% (mean ± SEM, 4 axons), respectively and leakage conductance increased to about five times of the control value. Higher concentrations of methylmercury chloride decreased the resting membrane potential. A concentration of 0.5 mM depolarizing the nerve membrane by 16 ± 2 mV (mean ± SEM, 3 axons) in 40 minutes. These changes in ionic conductances and membrane potential were irreversible on washing the axon with drug-free sea water.     

Cadherin-mediated cell-cell adhesion and tissue segregation in relation to malignancy

We review evidence concerning the basis for tissue segregation during embryonic development. This compartmentalization is shown to be an immiscibility phenomenon caused by changes in the strengths of adhesions between mobile cells which accompany their differentiation and generate interfacial tensions at cell population boundaries. The mobile cells exchange neighbors in response to these adhesion-generated forces which impel the system toward the configuration of maximal binding. Cadherins dominate these intercellular adhesions, but integrin-fibronectin-based adhesions also contribute to them as well as to cell-matrix adhesions. At the interface between two segregating cell populations are three kinds of cell-cell interfaces: a-a, b-b and a-b. Tissue immiscibility (segregation) results when the cross-adhesion is weaker than the mean value of the two kinds of self-adhesions, does not require (although it permits) qualitative changes in cell adhesion molecules and is easily generated even by moderate changes in the quantities of adhesion molecules on the cell surfaces. All type I and II cadherins tested cross-adhere, in most cases with strengths close to those of their self-adhesions. Is malignant invasion a process of cell segregation in reverse, in which the cross-adhesion between cancer cells and host tissue components is strong relative to their self-adhesions? We review evidence for cadherin involvement in breast, prostate and brain cancers. Despite evidence that N-cadherin enhances the invasiveness of certain cancer cells, we have found that increasing the expression not only of functional E-cadherin but also of P- or N-cadherin restrains the spreading of other malignant cell lines over (and through) a reconstituted extracellular matrix.