Animal development

Interestingly, prolonged duration of the first embryonic M phase is also observed in other mammalian and non-mammalian embryos. It was found in rabbit embryos (X. Yang M. Deng, personal communication) and in sea urchin embryos (J. Z. Kubiak P. Cormier, unpublished observation). Further studies will show whether it is a rule during animal development. 

Prion transmission between species is limited by a barrier. A species barrier restricts transmission of prion disease between different mammalian species. On primary passage of prions from species A to species B, usually not all inoculated animals of species B develop disease, and those that do have much longer and more variable incubation periods than those that are seen with transmission of prions within the same species. On second passage of infectivity to further animals of the species B, transmission parameters resemble within-species transmissions, with most if not all animals developing the disease with short and consistent incubation periods. Species barriers can therefore be quantified by measuring the fall... 

The traditional long-term bioassays use highly inbred animals, developed with the goal of reducing the variability in background tumor incidences as a means of... 

Both male and female tsetse live solely on vertebrate blood, and the various species that carry sleeping sickness typically feed not only on humans but also on both domestic and wild animals. Infected flies pass on trypanosomes whenever they take a blood meal, so that the parasites not only move between flies and humans, but also infect a number of other hosts. Infected domestic animals develop nagana, but wild animals may show no sign of illness. They serve instead as healthy animal reservoirs of trypanosomes, permitting tsetse flies to pick up the parasites at any time without necessarily feeding on infected humans or domestic animals. For this reason and also because available drug therapies have proved no more practical here than for leishmaniasis, control of trypanosomiasis has long emphasized eradication of tsetse flies. 

Despite the misfortunes of these addicts, MPTP has proved an invaluable tool for studying the biology of Parkinson s disease. When MPTP is injected into experimental rats, mice, or monkeys, neurons in the substantia nigra of these animals start to die, and the animals develop motor problems that closely resemble the symptoms of Parkinson s disease. Researchers hope to use MPTP in animals to unravel the mystery of what causes Parkinson s disease in humans, in the hope that they can develop a cure for this devastating disease. 

In ecology, ecosystems are really examples of steady state systems. Ecosystems involve a flow of energy in only one direction, from the Sun. Nevertheless, populations of plants and animals develop stable numbers that react to external changes, such as disease and variations in the weather. For example, if the number of carnivores in an ecosystem increases, more herbivores are eaten and the herbivore population decreases. 

The second family of secreted proteins that is covalently lipidated is the family of Wnt proteins. They are also involved in numerous processes like proliferation of stem cells, specification of the neural crest, and the expanding of specific cell types. The correct regulation of this pathway is important for animal development. Willert and coworkers were the first to isolate an active Wnt molecule. Mass spectroscopy studies carried out with the isolated protein revealed that cysteine 93 is palmitoylated. Mutating this amino acid to alanine led to almost complete loss of the signaling activity. Later in 2006, a second lipidation was found on a serine in Wnt3a. " In this case, the hydroxyl side chain is acylated with palmitoleic acid. This unsaturated fatty acid seems to be crucial for the progression of the protein through the secretory pathway. The attachment of two different lipid chains may therefore serve different functions. ... 

Notice that we have been forced to this conclusion even though 14% (7/50) animals developed liver tumors This is a very large risk. The human risk of developing any kind of cancer over a lifetime is near 40%, and here we have one chemical producing a 14% incidence in this small group of test animals, and we cannot validly call it a... 

In a lifetime dermal oncogenesis study in mice, 20 mg EHA in acetone was applied 3 times weekly for their lifespan. There were 40 mice in the group at the start of the study. Two animals developed squamous cell carcinomas, and four other animals had squamous cell papillomas. The first tumor was observed after 11 months of treatment. None of the acetone-treated controls developed tumors. There was an apparent increase in the frequency of chronic nephritis in the EHA-treated mice (68% compared with 15% in controls). Treatment with EHA may have exacerbated the onset and development of this condition, which is normally seen in aged mice. 

Exposure of guinea pigs to 2530 ppm for 4 hours was lethal to more than half of the animals death usually was delayed and a result of pulmonary edema effects were irritation of the eyes and the nose, lacrimation, tremor, dyspnea, and narcosis some surviving animals developed a delayed but profound anemia. ... 

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