Presence of SH-Compounds in Non-Developing Embryos

Abstract

Hammett 1 points out that the —SH group is the essential chemical stimulus for cell division. He also concludes 2 that the greater the natural cell division activity the greater the degree of reaction to the chemical groups. Coldwater 3 regards the nitroprusside reaction as indicating the presence of protein-fixed —SH groups, and finds a high concentration of this sulphydryl in areas of regenerating tissues undergoing proliferative growth. Thompson and Voegtlin, 4 Murray, 5 and Yaoi 6 have found the glutathione content of embryos of the chick and rat to be at a maximum in early development and to decrease with age.

One might infer from the above that if embryos were tested for the —SH groups at periods of marked cellular activity a much stronger reaction would be obtained than if they were tested at periods of relative inactivity. The embryo of the grasshopper, Melanoplus differentialis, is favorable material for this test as it can be obtained in large numbers, is easily dissected out, and is so small that it is quickly saturated with the sodium nitroprusside. Its development may be divided into 3 definite periods. First, a period of rapid embryonic growth for 21 days (at 25°C.) which is followed by a period of apparent inactivity lasting from a few days to several months. This period (diapause) is marked by the lack of any movement, absence of mitosis (Slifer 7 ) and very low rates of respiratory metabolism (Bodine 8 ). The third period begins with the resumption of mitotic activity followed by blastokinesis. After the embryo has revolved, it grows rapidly and engulfs the remaining yolk. The third phase marks the completion of differentiation and embryonic organogenesis.