Carbonic anhydrase activity in early developing chick embryos.

CHANGES in tension of environmental CO2 gas have been shown to affect cellular differentiation. In the presence of increased partial pressure of dissolved CO2(/?Co2) Loomis (1957) has demonstrated an increase in sexual differentiation of hydra and Flickinger (1958) has caused explanted frog ectoderm to differentiate into neural tissue. Loomis was able to show that the substance which stimulates sexual differentiation in crowded cultures of Hydra littoralis is dissolved CO2 gas. Flickinger could produce a definite increase of neural tissue induction by bubbling CO2 gas through the culture media for a 10-20-minute period. Trinkaus & Drake (1959) have reported an analysis of the stimulating effect of pCot o n development of the embryo of Fundulus heteroclitus. For these reasons it seemed important to study an enzyme which utilizes CO2 as a substrate. The appearance of carbonic anhydrase activity in early developing embryos which are producing CO2 might lead to a reduced CO2 tension (H2O+ CO2±^H2CO3). In turn this activity could control development by slowing cellular differentiation. Previous measurements of carbonic anhydrase activity in chick embryos have dealt mainly with embryonic organs after the 4th day. Van Goor (1940) and Clark (1951) have shown a rise in retinal activity between the 4th and 6th days and both have failed to find activity in blood before the 11th day. The absence of enzyme activity in blood greatly simplified the measurement in tissue by obviating corrections for erythrocyte carbonic anhydrase. This report deals with values for whole chick embryo carbonic anhydrase from 1 \ days (stage 8) to 19 days (stage 45) and relates the activity to weight and content of protein and nitrogen. In addition, the intracellular particulate localization of protein, nitrogen, and carbonic anhydrase activity has been studied in embryos from 1£ days to 6£ days. Preliminary studies have also been made of the localization of activity in the organ systems of the early embryo.