Effects of Purine and Pyrimidine Analogues on Development of Rana pipiens

Abstract

Analogues of the purine and pyrimidine constituents of the nucleic acids have been found to have a variety of biological effects which may be ascribed to various types and degrees of interference with the biosynthesis of nucleic acids and related compounds (1).

The desirability of testing such antimetabolites on a variety of biological species and systems has previously been mentioned(l) for such studies contribute both to the comparative biochemistry of nucleic acid metabolism and to the knowledge of the mode of action of the antimetabolites. The present report is concerned primarily with an extension of the antimetabolite studies to the problems of chemical embryology. Although the effects of some antimetabolites on the development of the chick have been studied, except for a brief attempt by Brachet(2) and a more recent preliminary report(3) amphibia have not been utilized for such studies. The amphibian egg lends itself readily to experimental and biochemical observations on early morphogenesis. The present investigation is concerned with the development of Rana pipiens embryos from fertilization to Shumway stage 25(4).

Methods. Eggs were obtained from female Rana pipiens by induced ovulation and were fertilized by a suspension of macerated frog testes in spring water. The twenty-five analogues were tested by immersing embryos chosen at the two cell stage in eight different concentrations of the compound (in the range of 1 to 25 mg per 100 ml) made up in spring water. Fifty embryos, 25 per finger bowl, were used for each concentration. The bowls were kept in an incubating refrigerator at 18-19°C during the course of the experiment. Readings of the developmental progress were taken at regular intervals and compared with those of appropriate controls.

The results are expressed in Table I in terms of the earliest stage of development which is inhibited by the analogue and the minimal effective concentration to produce complete inhibition at this point.