Nucleic acid synthesis and turnover in tissue culture.

It has been demonstrated (1) that the cultivation of embryonic chick tissues in roller tubes in the presence of an extract of chick embryo resulted in an increase in the protein content of the cultures. Histological examination of the tissue revealed a progressively diminishing cellular density in the tissue following cultivation in embryo extract. This decrease in the cellular concentration of the tissue is not apparent from the changes in total protein content, for no distinction is made between intracellular and extracellular protein. Since desoxypentose nucleic acid (DNA) and pentosenucleic acid (PNA) are intracellular constituents, nucleic acid analysis provides a chemical method for measuring the quantity of nuclear and cytoplasmic substance present in a culture. Nucleoprotein phosphorus analysis was first suggested and used by Willmer (2) to measure growth in tissue culture. At that time methods for fractionation and separation of DNA and PNA were unknown. Davidson and Waymouth (3) and later Hull and Kirk (4) studied changes in DNA and PNA in chick embryo heart cultures in roller tubes. The increments of DNA and PNA obtained by analysis of tissue cultures are not a true measure of new cell production, since the quantities found are the net result of the loss of nucleic acid from the original tissue and the increase associated wit,h the formation of new cells. A reliable index of new cell production (4) can be obtained by measuring the quantity of P32 incorporated into the DNA which is not in dynamic equilibrium with other sources of phosphorus in the cell. The present paper describes the changes in total DNA and PNA in roller tube cultures of chick heart, lung, and intestine. In addition the