Accumulation of an organ-specific protein during development of the embryonic chick brain.

In an earlier investigation by the present authors (Friedman & Wenger, 1965) the quantitative development of brain-specific antigens in chick embryos was studied using antisera against whole brain homogenates. The antisera employed were made brain specific by absorption with homogenates of various chicken tissues. Based on this study, the period between 5£ and 12 days of incubation, stages 28 and 38 of the Hamburger & Hamilton (1951) stage series, was considered to be critical for neural differentiation. Previous studies of the development of brain-specific antigens had generally employed qualitative precipitin tests or specific inhibition of differentiation by antisera and did not measure the accumulation patterns of these antigens (Schechtman, 1948; Ebert, 1950; Flickinger, 1958; McCallion & Langman, 1964). An opportunity to study the differentiation of the brain with respect to a single, well-characterized tissue-specific protein was presented by the isolation from beef brain of a unique protein termed 'S-100' because of its solubility in 100 % saturated ammonium sulfate (Moore & McGregor, 1965; Moore, 1965). This highly acidic protein becomes immunogenic when complexed with methylated bovine serum albumin (Levine & Moore, 1965) thereby providing the means for such a study. It had been shown that S-100 protein exhibited relatively little serological variation among a wide range of vertebrate species (Levine & Moore, 1965; Kessler, Levine & Fasman, 1968). This permitted use of antisera against bovine brain S-100 in an assay for the presence of a similar protein in embryonic chicken brain. The present study, employing antisera against a single brain-specific protein and a highly sensitive, quantitative microcomplement-fixation test, confirms and extends earlier results obtained with absorbed antisera against crude homogenates. 1 Author's address: Department of Biology, University of Missouri at St Louis, St Louis, Missouri 63121, U.S.A. 2 Author's address: Department of Anatomy, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.