Methylation of DNA in developing embryos of the sea urchin Psammechinus miliaris

Embryos of the sea urchin Psammechinus miliaris have been labelled after fertilization with [6(-3)H]uridine and cultured in filtered sea water. 32-cell, blastula, gastrula and pluteus stages were harvested. The DNA from these embryos was purified and hydrolyzed and the nuclear bases were analyzed by means of high performance liquid chromatography. The ratios of 5-methylcytosine and cytosine demonstrate that the concentrations of 5-methylcytosine are essentially the same in the developmental stages examined (gamma = 95%), which contradicts the hypothesis that methylation of DNA plays a role in cell differentiation.