Nucleic acid changes in the mouse during gestation.

The nucleic acid changes during embryonic development have been stucliecl by several investigators (l-4). It is now generally agreed that a rapidly growing tissue has a high concentration of nucleic acid (5). Thus, in the avian embryo, the concentrations of pentose nucleic acid (PNA) and clesoxypentose nucleic acid (DNA) increase during the time of the most rapid growth of the tissue (6, 7). Similar results were obtained with the sheep embryo (8). While the present study was in progress, Geschwind and Li (9) reported their observations on rat liver. They found that in the fetal liver the ratio of PNA phosphorus to DNA phosphorus remains constant from the 16th through the 19th day of gestation. After birth, it rapidly rises until the young are weaned. Surprisingly enough, in spite of the extensive work carried out in this field, no one has, to our knowledge, studied the changes of nucleic acid in the maternal tissues during gestation. Therefore, it seemed to us of particular interest to investigate this aspect of the problem, and also to reexamine the relationship of nucleic acid to growth in the mammalian embryo with the aid of improved analytical methods now available. The results of this study are reported in the present communication.