Quantitative Development and Molecular Forms of Acetyl‐and Butyrylcholinesterase During Morphogenesis and Synaptogenesis of Chick Brain and Retina

Abstract

The embryonic development of total specific activities as well as of molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) and of butyrylcholinesterase (BChE, EC 3.1.1.8) have been studied in the chick brain. A comparison of the development in different brain parts shows that cholinesterases first develop in diencephalon, then in tectum and telencephalon; cholinesterase development in retina is delayed by about 2–3 days; and the development in rhomb‐encephalon [not studied until embryonic day 6 (E6)] and cerebellum is last. Both enzymes show complex and independent developmental patterns. During the early period (E3‐E7) first BChE expresses high specific activities that decline rapidly, but in contrast AChE increases more or less constantly with a short temporal delay. Thereafter the developmental courses approach a late phase (E14‐E20), during which AChE reaches very high specific activities and BChE follows at much lower but about parallel levels. By extraction of tissues from brain and retina in high salt plus 1% Triton X‐100, we find that both cholinesterases are present in two major molecular forms, AChE sedimenting at 5.9S and 11.68 (corresponding to G₂ and G₄ globular forms) and BChE at 2.9S and 10.3S (G₁ and G₄, globular). During development there is a continuous increase of G₄ over G₂ AChE, the G₄ form reaching 80% in brain but only 30% in retina. The proportion of G₁ BChE in brain remains almost constant at 55%, but in retina there is a drastic shift from 65% G₁ before E5 to 70% G₄ form at E7. Our results show that the light‐molecular‐weight forms of both enzymes are prevalent during the morphogenetic period, whereas the G₄ forms correlate with final differentiation processes, e.g., synaptogenesis.