Chick explants

Kulesa, P. 1998. Neural crest cell dynamics revealed by time-lapse video microscopy of whole chick explant cultures. Dev. Biol. 204, 327-344. 

Couchman, J.R., Rees, D.A. (1979). The behavior of fibroblasts migrating from chick heart explants Changes in adhesion, locomotion and growth, and in the distribution of actomyosin and fi-bronectin. J. Cell Sci. 39, 149-165. 

Ascorbic acid stimulates proliferation of rabbit chondrocytes at high cell density, chick embryo and bovine articular chondrocytes, and rabbit cartilage explants. Although evidence suggests that ascorbic acid treatment does not directly stimulate transcription of ECM products, cultured chondrocytes undergo changes in gene expression characteristic of hypertrophy. 

Explanted chick embryos at presomite or multiple somite stages or chick embryonic parts are cultured with the test agent incorporated into the culture medium and evaluated for growth and differentiation. 

Mouse and chick bone explants have been shown to produce a latent collagenase.33,34 jn addition, the mouse bone explants produce a latent neutral proteinase. Limited proteolysis of these molecules gives rise to proteoglycan and collagen degrading action. Latency may be due to the presence of an enzyme inhibitor complex. The chick latent collagenase has an apparent MW of 54,000, while the active form has an MW of 43,000. 3 Trypsin activation of both latent mouse enzymes decreases their MW s from 60-70,000 to about 40,000. The mouse neutral protease is inhibited by EDTA, cysteine, and serum.34... 

The most definitive evidence for a role for che-motropism in axon guidance in vertebrates has come from in vitro systems in which neural explants or individual neurons have been shown to send neurites in the direction of the source of a diffusible chemical. For example, the growth cones of chick dorsal-root ganglion neurons orient towards increasing concentrations of nerve growth factor (Letoumeau, 1978 Gunderson and Barrett,... 

Commissural axons from the embryonic rat spinal cord extend preferentially toward floorplate explants in a manner suggestive of a chemotropic mechanism (Tessier-Lavigne et al., 1988 Placzek et al., 1990). Recently, two closely-related proteins isolated from embryonic chick brains, netrin-1 and netrin-2, have been shown to possess chemotropic activity in this spinal cord assay system (Serafini et al., 1994 Kennedy et al., 1994). 

Newgreen, D. (1984) Spreading of explants of embryonic chick mesenchymes and epithelia on fibronectin and laminin. Cell Tissue Res. 236 265-277. 

Fig. 29. Double refraction of collagen fibers produced by fibroblast cultures of chick embryo explants, after Pfeiffer (172). Retardation, r, in m/t is plotted, as ordinate, against the refractive index, n, of the immersion medium. Curve A is for fibers fixed in Helly s fluid (containing formalin), and curve B shows the result of fixation in tannic acid.

Biosynthesis. — Up to 56% of sulphated glycosaminoglycans synthesized by explant cultures of human and rabbit articular chondrocytes are located in the trypsin-digestible pericellular coat. ° Sulphate is incorporated into both D-glucopyranosyluronic acid and L-idopyranosyluronic acid residues in hybrid glycosaminoglycans by monolayers of chick embryo arterial fibroblasts. Several oligosaccharides, released on treatment with chondroitin lyase ABC and chondroitin lyase AC, have been characterized. 

Hayashi and Herrmann (1959), working with chick embryo explants of 11-13 somites, provided the first quantitative estimates of embryo growth on a defined medium. During 24 hours of culture, embryo growth as measured by DNA and protein glycine accumulation was not only... 

A preliminary series of experiments with chick embryo explants cul-tered on dextran medium suggested that all regions of the embryos were not affected to the same extent by protein starvation. In order to quantitate this response, procedures were developed which would allow the dissection of embryos into brain, neural tube, somite, heart, and extraembryonic membrane (area opaca plus area pellucida) in a reproducible manner so that the quantities of DNA, RNA, and protein in these regions could be determined. Relative to embryo explants cultured on whole egg homogenate medium, in those cultured on protein starvation medium the accumulation of macromolecules in the brain region was most restricted and the heart least. 

As an initial approach to an analysis of the basis for the differences between embryo regions in their apparent sensitivity to protein starvation the breakdown of protein was studied (Klein et al., 1971). Chick embryos of 11-13 somites were exposed to C-labeled amino acids for 3 hours in buffered chick Ringer s salt solution. Explants were next cultured for 6 hours on semi-solid medium to reduce the level of free [ C]amino acids and to allow protein labeling to increase. They were then transferred to either whole egg homogenate growth medium or protein starvation medium. Explants were cultured for various periods up to 48 hours and dissected regions were analyzed for protein radioactivity and the radioactivity soluble in 5% trichloroacetic acid. Protein and DNA contents were also determined. 

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