Amphibian embryo

Pauli, B.D., Coulson, D.R., BerriE, M. (1999) Sensitivity of Amphibian Embryos and Tadpoles to Mimic 240 LV Insecticide Following Single or Double Exposures. Environmental Toxicology and... 

The majority of analyses on neural crest cell migration, proliferation, and differentiation have been carried out in avian and amphibian embryos because of the relative ease of experimental manipulation (see Le Douarin, 1982). These experiments demonstrated that pigment cells arise from the neural crest. When pieces of neural folds were grafted to the... 

Amphibian embryos are more sensitive to zinc than older stages developmental abnormalities were evident in most species at concentrations >1.5 mg Zn/L (Table 9.6). Embryos of the narrowmouthed toad (Gastrophryne carolinensis) seem to be especially sensitive, with adverse effects reported at 10 pg Zn/L (USEPA 1987), but this requires verification. Amphibians, along with other taxonomic groups, were rare or absent in the vicinity of zinc smelters when compared to more distant sites (Beyer et al. 1985). 

Sandworm FLUORANTHENE Amphibians embryos and larvae embryos exposed from early development through hatching under artificial ultraviolet light newly hatched larvae were exposed outdoors in varying sunlight intensity levels >1000 LC50 (96 h) 2... 

Hatch, A.C. and G.A. Burton, Jr. 1998. Effects of photoinduced toxicity of fluoranthene on amphibian embryos and larvae. Environ. Toxicol. Chem. 17 1777-1785. 

Immunotoxic Effects of Environmental Chemicals on Amphibian Embryos... 

Unlike mammalian embryos that are protected within the uterus, amphibian embryos are protected only by a fertilization membrane and jelly coat. Although there is some... 

The cell cycle is a key process that recurs in a periodic manner. Early cell cycles in amphibian embryos are driven by a mitotic oscillator. This oscillator produces the repetitive activation of the cyclin-dependent kinase cdkl, also known as cdc2 [131]. Cyclin synthesis is sufficient to drive repetitive cell division cycles in amphibian embryonic cells [132]. The period of these relatively simple cell cycles is of the order of 30 min. In somatic cells the cell cycle becomes longer, with durations of up to 24 h or more, owing to the presence of checkpoints that ensure that a cell cycle phase is properly completed before the cell progresses to the next phase. The cell cycle goes successively through the phases Gl, S (DNA replication), G2, and M (mitosis) before a new cycle starts in Gl. After mitosis cells can also enter a quiescent phase GO, from which they enter Gl under mitogenic stimulation. 

The interplay between oscillations and bistability has been addressed in detailed molecular models for the cell cycles of amphibian embryos, yeast and somatic cells [138-141]. The predictions of a detailed model for the cell cycle in yeast were successfully compared with observations of more than a hundred mutants [142]. Other theoretical studies focus on the dynamical properties of particular modules of the cell cycle machinery such as that controlhng the Gl/S transition [143]. 

Turin L, Warner AE Carbon dioxide reversibly abolishes ionic communication between cells of early amphibian embryo. Nature 1978 270 56-57. 

There are several examples of mitosis and/or cell division in the absence of cell expansion—the early pregastrula cleavages of amphibian embryos the septa-tion of free-floating nuclei in liquid endosperm and the internal divisions of large, free-floating cells in liquid culture (26, 29). In such cases there must be specific cytokinetic or mitotic factors, the action of which need not be related in any way to cell expansion. 

The same problem is also posed by multicellular embryos. How do cells become different and arranged in their proper positions At that time, it was not possible to pull apart the cells of vertebrate embryos because disaggregation treatments had not been devised. (Similar experiments to those of Wilson on amphibian embryos were not carried out until the 1950s). It was possible, however, to separate individual cells at very early stages when a fertilized egg had only divided a few times, and rearrange them. These early experiments indicated that position within the embryo was paramount in determining how a cell should behave. 

Figure 26.4 Abiotic and biotic interactions leading to the indirect toxicity of chlorofluorocarbons to amphibians. Atmospheric release of chlorofluorocarbons causes the depletion of the stratospheric ozone layer (abiotic-abiotic interaction). Depleted ozone allows for increased penetration of UV-B radiation (abiotic-abiotic interaction). UV-B radiation alone and in combination with fungus (abiotic-biotic interaction) causes increased mortality of amphibian embryos.

J.M. Kiesecker, A.R. Blaustein (1995). Synergism between UV-B radiation and a pathogen magnifies amphibian embryo mortality in nature. Proc. Natl. Acad. Sci. U.S.A., 92,11049-11052. 

In avian, mammalian and amphibian embryos, PG molecules, chiefly CS-PG, have been localized with positively charged dyes, such as alcian blue (Pintar, 1978 Derby, 1978 Erickson and Weston, 1983 Tucker, 1986) and ruthenium red (Hay,... 

These studies show, in avian and amphibian embryos at least, that although CS-PG is widely distributed, there is a strong correlation between local maxima and areas of ECM not occupied by crest cells. 

Boucaut, J.C., Darribere, T., Poole, T.J., Aoyama, H., Ya-mada, D.M. and Thiery, J.P. (1984) Biologically active peptides as probes of embryonic development a competitive peptide inhibitor of fibronectin function inhibits gastru-lation in amphibian embryos and neural crest cell migration in avian embryos. J. Cell Biol. 99 1822-1830. 

Epperlein, H.H.E., Halfter, W. and Tucker, R.P. (1988) The distribution of fibronectin and tenascin along migratory pathways of the neural crest in the trunk of amphibian embryos. Development 103 743-756. 

The majority of smdies that examine shifts in life-history traits in amphibians focus on the shift from the tadpole to the juvenile stage. One stage that is often overlooked is the embryonic stage. The embryonic stage is viewed as a simple developmental stage, however, there is evidence that shows that amphibian embryos can detect and respond to cues from predators in their environments. The aim of this paper is to provide a review of studies that have examined life-history shifts in amphibian embryos in response to chemical cues from predators. From the results of these studies, we will develop generalized hatching patterns that may be used to predict these shifts in other amphibian species. We will also discuss the complexity and specificity of the chemical cues involved and lastly we will examine those results which do not fit into our hypothesized patterns and address why there is variability in life-history responses. 

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