Quantitative determination of desoxyribonucleic acid in echinoderm germ cells

Abstract

1. 1. Nuclei were isolated from Asterias forbesii oocytes in the germinal vesicle stage and the thymine content per nucleus found to be about six times the amount in the sperm of the same species. 2. 2. Approximately the same yields of thymine were obtained by digesting sperm with 2 N HClO 4 under reflux for five hours and with 12 N HClO 4 for one hour. 3. 3. The amount of thymine in the sperm of Tripneustes ventricosus was found to be 12.14 × 10 −8 μg per cell. 4. 4. The DNA-thymine content of a preparation of mature unfertilized Tripneustes ventricosus eggs was determined by the isotope dilution method using C 14-thymine of high specific activity in which all of the carbon atoms were uniformly labelled. All of the thymine found could be attributed to contaminating somatic nuclei, the number of which could be determined accurately, and to the polar bodies leaving none that could be assigned to the egg cells. Calculations made by setting the parameters not at the observed means but at the extremes of the range indicated by the standard errors gave the result that the amount of DNA-thymine in the egg could not be more than 6 per cent of the amont found in the sperm. 5. 5. The nuclei of the mature unfertilized eggs of Tripneustes, like those of Arbacia and Asterias, gave a negative Feulgen reaction. After centrifugation at 78,000 g for 20 minutes nuclei of mature Arbacia eggs still gave a negative Feulgen reaction. 6. 6. Reasons are given for concluding that DNA cannot be the primary genic material. 7. 7. A hypothesis is presented giving the probable role of DNA and DNA-derivatives in the nucleus and the cytoplasm. A number of biological phenomena are interpreted in terms of this hypothesis.