Mammals embryo

Amphi-bians Chicken Mouse Rat Hamster Rabbit Other mammals Embryo- Terato-genic toxic... 

Unchanged p,p -DDT tends to be lost only very slowly by land vertebrates. There can, however, be a certain amount of excretion by females into milk or across the placenta into the developing embryo (mammals) or into eggs (birds, reptiles, and insects). 

Pesticides accumulate in fetal cells and reproductive organs in mammals, birds, and fish due to biochemical processes. This is noted especially often for OCPs, which were observed in large amounts (up to 6.8 mg/kg) in, for example, the sexual organs of hares, rabbits, pheasants, green-winged teals, and in white-eyed and red-headed ducks. They were found in animal embryos, as well as in black thrush eggs and in pheasant embryos and amniotic fluid (up to 73.0 mg/kg) [3]. 

This suggests that cyclin A2 is not essential for the early embryonic cell cycles. Also D-type cyclins seem to be dispensable for the early mouse embryo cell cycle progression since embryonic stem (ES) cells do not express them at all before differentiation (Savatier et al 1996). We do not know, however, whether the D-type cyclins are also absent in the early embryo. These observations suggest that not only could the first cell cycles of the mouse embryo have specific modifications, but also further embryonic cell cycles are specifically modified as well. Mammalian embryonic cell cycles are probably modified often during development. Such studies could allow us to determine a profile of a minimal cell cycle in mammals which must, however, be much more complex than a simple S M phase embryonic cell cycle of amphibians or insects. 

Currently, only the Hydra system incorporates a measurement of toxicity to the adult to provide a comparison of the sensitivity of the embryo with that of the adult (Johnson et al., 1988). However, the Hydra screen has not been fully validated as being predictive of results in mammals, and has fallen from favor. Thus, a major goal of research directed toward developing an in vitro teratogen screen should be to find a simple yet appropriate measure of toxicity unrelated to development. This would allow the comparison of the dose for a 50% effect (ED50) on developmental toxicity as measured in vitro to an ED50 for adult toxicity in vitro. The validation... 

Significant concentrations of cyanotoxins have been found to accumulate in the tissues of macroinvertebrates such as mollusks and crustaceans, presenting an indirect route of exposure for invertebrates, fish, and aquatic mammals at higher trophic levels (Negri and Jones 1995). In natural systems, mortality among benthic invertebrate herbivores is probably low because most bloom-forming bacteria are planktonic and only periodically come into contact with the benthos. Nevertheless, Kotak et al. (1996) determined that enhanced mortality of snails at the end of a bloom cycle in Canadian lakes was due to consumption of Microcystis cells that had formed a scum on the surface of macrophytes. Oberemm et al. (1999) found that aqueous microcystins, saxitoxins, and anatoxin-a all resulted in developmental delays in fish and salamander embryos. Interestingly, more severe malformations and enhanced mortality were observed when larvae were exposed to crude cyanobacterial extracts than to pure toxins applied at natural concentrations (Oberemm et al. 1999). 

The genic pattern of a fertilized egg cell determines what the developing embryo is going to need during the course of its development. In certain species of mammals (e.g., rats), the over-all nutritional needs are qualitatively different from those of other species (e g., guinea pigs). In each individual within the human species, the needs are quantitatively different. 

Actually ESC, obtained from the embryoblast of pre-implantation embryos of mammals ... 

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