Functional expression of the human transferrin receptor cDNA in Chinese hamster ovary cells deficient in endogenous transferrin receptor

Transferrin (Tf) receptor-variant Chinese hamster ovary cells have been isolated by selection for resistance to two Tf-toxin conjugates. The hybrid toxins contain Tf covalently linked to ricin A chain or a genetically engineered diphtheria toxin fragment. The Tf-receptor-variant (TRV) cells do not have detectable cell-surface Tf receptor; they do not bind fluorescein-Tf or 125I-Tf. TRV cells are at least 100-fold more resistant to the Tf-diphtheria toxin conjugate than are the parent cells. The TRV cells have retained sensitivity to native diphtheria toxin, indicating that the increased resistance to the conjugate is correlated with the loss of Tf binding. The endocytosis of fluorescein-labeled alpha 2-macroglobulin is normal in TRV cells, demonstrating that the defect does not pleiotropically affect endocytosis. Since these cells lack endogenous Tf receptor activity, they are ideally suited for studies of the functional expression of normal or altered Tf receptors introduced into the cells by cDNA transfection. One advantage of this system is that Tf binding and uptake can be used to monitor the behavior of the transfected receptor. A cDNA clone of the human Tf receptor has been transfected into TRV cells. In the stably expressing transfectants, the behavior of the human receptor is very similar to that of the endogenous Chinese hamster ovary cell Tf receptor. Tf binds to cell surface receptors, and is internalized into the para-Golgi region of the cell. Iron is released from Tf, and the apo-Tf and its receptor are recycled back to the cell surface. Thus, the TRV cells can be used to study the behavior of genetically altered Tf receptors in the absence of interfering effects from endogenous receptors.     

Scats and den contents as indicators of the diet of stoats (Mustela erminea) in the Tasman Valley,South Canterbury,New Zealand

Stoats are significant predators of native fauna in New Zealand. They occur in many habitat types and consume a wide range of prey. The diet of stoats in the Tasman River, South Canterbury, was studied by analysis of scats and den contents. Analysis of 206 scats showed that stoats ate mainly lagomorphs, birds and invertebrates. Minor components included mice, lizards, fish and hedgehogs. Stoats ate more birds in spring than in autumn, and female stoats ate more invertebrates than did males. The contents of 219 dens collected in the same area at the same time provided further information. Birds and lagomorphs occurred at high frequency in dens, and other components were minor. Remains in dens were larger than in scats and allowed identification of many more prey items to species level. Den contents revealed a potentially substantial impact of stoats on threatened shorebirds locally; this impact was not detected by analysis of scats.     

A community-level evaluation of the impact of prey behavioural and ecological characteristics on predator diet composition

Although predation avoidance is the most commonly invoked explanation for vertebrate social evolution, there is little evidence that individuals in larger groups experience lower predation rates than those in small groups. We compare the morphological and behavioural traits of mammal prey species in the Taï forest, Ivory Coast, with the diet preferences of three of their non-human predators: leopards, chimpanzees and African crowned eagles. Individual predators show marked differences in their predation rates on prey species of different body sizes, but clear patterns with prey behaviour were apparent only when differences in prey habitat use were incorporated into the analyses. Leopard predation rates are highest for terrestrial species living in smaller groups, whereas eagle predation rates are negatively correlated with group size only among arboreal prey. When prey predation rates are summed over all three predators, terrestrial species incur higher predation rates than arboreal species and, within both categories, predation rates decline with increasing prey group size and decreasing density of groups in the habitat. These results reveal that it is necessary to consider anti-predator strategies in the context of a dynamic behavioural interaction between predators and prey.