Two Acidic Proteins Associated with Brain Development in Chick Embryo

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Abstract
The developmental chages in protein composition of the chick optic tectum were analyzed by 2-dimensional gel electrophoresis. Staining with Coomassie Brilliant Blue R revealed 54 major proteins, 8 of which remarkably changed their abundance during development. Four of these proteins (S8, S14, S30 and S54) increased and 2 of them (S7 and S37) decreased in the course of the brain development. The other 2 proteins (S5 and S6) appeared at specific embryonic stages and were not detected in the adult. The abundance of S5 protein was highest at day 7, and that of S6 protein at days 9-18. The 2 proteins were present in other regions of the embryonic brain but were not detected in the embryonic liver. The proteins were purified from the soluble fraction of embryonic chick brains by pH 5.5 precipitation, DEAE-Sepharose column chromatography, ammonium sulfate precipitation, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. MW of S5 and S6 proteins were 95,000 and 100,000, respectively, and their isoelectric points were about 4.5. They were compared by peptide mapping using V8 protease and found to share 11 common peptides out of 17 distinct ones. This indicates a strong degree of structural homology between these two proteins.