Development of glutamine synthetase (GS) activity in the chick embryo retina has proved to be a useful system for studying control mechanisms in animal cells (6, 12, 2, 21) . The enzyme activity rises rapidly late in embryonic development (16) and can be induced prematurely both in culture and in ovo by a variety of steroids (10, 11, 7) . Piddington and Moscona (9) have shown that the time of G...

The secretory capacity of the chick embryo adrenal was investigated at different stages of its development employing a sensitive bioassay for corticosteroids based upon the modifications produced in vitro by these hormones on the height of the chick embryo duodenal mucosa. The adrenal gland cultivated in contact with explants of duodenum and stimulated with increasing doses of ACTH exhibited a ...

The secretory capacity of the chick embryo adrenal was investigated at different stages of its development employing a sensitive bioassay for corticosteroids based upon the modifications produced in vitro by these hormones on the height of the chick embryo duodenal mucosa. The adrenal gland cultivated in contact with explants of duodenum and stimulated with increasing doses of ACTH exhibited a ...

Chick embryo extract is widely used to induce differentiation in cultures of muscle and other tissues. As part of a systematic study of factors which promote maximal differentiation of muscle cells, we found that unmodified chick embryo extract could be quite toxic to cells. This report describes the effects of varying culture media composition and cell density on the rate and extent of differe...

The effects of papain protease and of vitamin A on explanted limb bone rudiments from 7- and 13-day chick embryos and fetal mice have been studied and compared. The incubation of cartilaginous rudiments from 7-day chick embryos in a solution containing papain and cysteine resulted in complete loss of the metachromasia of the cartilage matrix within 1 hour; explants treated in this fashion recov...

The chick embryo – past, present and future as a model system in developmental biology 1011 PART I: The chick as a classical system for the study of development L. Wolpert (UK) Much more from the chicken's egg than breakfast – a wonderful model system 1015 C. Tickle (UK) The contribution of chicken embryology to the understanding of vertebrate limb development 1019 L. Wittler, M. Kessel (German...

1. The changes in the net amounts of retinol, retinyl esters and retinal in both the developing chick embryo and the newly hatched chick were investigated. The embryo requires about 68nmol of the vitamin for its growth, whereas the baby chick requires about 108nmol during the first 7 days after hatching. 2. Retinal was present in the egg in fairly high concentrations at the beginning of the inc...

The intramembrane organization of the plasma membranes of nonmalignant cells in culture has been compared by freeze-fracturing with that of virally-transformed malignant cells. No dramatic differences are present in the distribution of intramembrane particles in the plasma membranes of these cells when the cells are examined without fixation or with mild fixation (glutaraldehyde treatment) prio...