Cholinesterase in embryonic development.

I. Cholinesterase (ChE) activity was studied histochemically during early development of the sea urchin, the amphibian, the chick and the rat embryo. After formalin fixation and embedding in water-soluble carbowax, the enzyme reaction was carried out in serial section. 2. Independent from innervation ChE appears in every embryonic blastema in a very early stage of development. It disappears from the embryonic cells after they have assembled into definite organ structures. Thus, ChE plays a role in embryonic development which is different from its known function in the adult. Therefore, ChE activity present in differentiating cells during a limited phase of development, is termed "embryonic cholinesterase". 3. Embryonic ChE was invariably found in cells engaged in morphogenetic movements. This observation has led us to suppose that the enzyme in involved in the regulation of cellular movements during development. 4. In particular, embryonic ChE is described in the following locations: a) During sea urchin gastrulation ChE is present in the primary mesenchymal cells emigrating from the blastula wall and in the archenteron cells which are known to bring about the invagination movement by contraction of their pseudopods. b) In the early chick blastoderm ChE active "droplet cells" are described which are supposed to emigrate from the epiblast layer in order to form the hypoblast. c) During development of notochord and somites, during closure of the neural tube and development of the head anlage, the close correlation of ChE activity with various morphogenetic movements is demonstrated: ChE appears during aggregation and desaggregation of epithelial compounds. The active bending of preexisting epithelial sheets, such as the neural plate, is also accompanied by ChE activity in epithelial cells...