Biochemical studies of chick brain development and maturation: I. Alterations in the macromolecule content and cell-free protein synthesis.

Changes in macromolecule content (DNA, RNA, and protein) and cell-free protein synthetic activity in chick brain developing from 9-day-old embryos to 1 1/2-year-old adults were studied in three brain regions: cerebrum, cerebellum, and optic lobes. The accumulation of DNA, RNA, and protein in three brain regions occurred each in its own characteristic pattern although three distinct phases could be observed. The most rapid accumulation always occurred during embryonic development followed by a slower accumulation from hatching to 3-mo. with very little or no change in the brain macromolecule content thereafter. In all three brain regions, the cell-free protein synthetic activity increased during embryonic development, reaching maximum around hatching then decreased substantially (50-70%) after hatching. Comparison of 18-day-old embryonic and 1 1/2-year-old adult brain tissue showed that there was no significant alteration in the relative proportion of membrane-bound and free ribosomes. When the products of cell-free protein synthesis by embryonic and adult brain preparations were compared by SDS polyacrylamide gel electrophoresis, it was found that the percentage of various proteins synthesized by embryonic brain tissue was very similar to that of the adult. It is concluded that the decrease in cell-free protein synthesis is due to a general decrease in the synthesis of all types of proteins rather than a decrease in a specific group or groups of proteins.