The origin of yolk-DNA inXenopus laevis

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Abstract
Xenopus laevis serum and plasma was found to contain an average of 25 μg DNA/ml. Isolated X. laevis oocytes incubated in medium containing 25 μg DNA/ml labeled with either 125I, 32P or 14C and from three different sources (bovine, E. coli and X. laevis), incorporated the label at an average rate of 0.11 ng·mm−·hr−1. Sucrose gradient fractionation of oocytes revealed that 40–75% of the acid-precipitable label incorporated was associated with the yolk platelets. Additional incubations of oocytes in unlabeled medium demonstrated that the DNA incorporated into the yolk platelets was undergoing turnover; only 20% of the yolk-associated DNA was still present after a one-week incubation. Our data suggest that yolk-DNA arises by the adventitious uptake of DNA present in the maternal serum by vitellogenic oocytes.