The Desoxyribose Nucleic Acid Content of Animal Nuclei

Abstract

The amount of desoxyribose nucleic acid (DNA) has been estimated in individual nuclei by microphotometric detns. of Feulgen-stained prepns. The technic and major variables of microscopic photometry are discussed, and also the specificity and quantitative aspects of the Feulgen reaction. It is concluded that measurements on Feulgen prepns., if properly carried out, can give accurate relative estimates of the amt. of DNA in nuclei. Measurements on a variety of tissues of mouse, frog, Ambystoma, and grasshopper indicate that DNA tends to occur in well-marked units characteristic of the sp. Most nuclei measured contained twice the DNA found in the haploid spermatids, but nuclei with 4, 8, and 16 times the haploid amt. were found in a no. of tissues. A study of mitosis in embryo mouse liver and Ambvstoma larva pronephros showed that DNA increases to twice the normal diploid amt. in interphase preceding the beginning of prophase, and is divided into two diploid nuclei at anaphase. Thus all prophase nuclei were found to contain 4 times, and telophase nuclei 2 times, the haploid amt. During spermatogenesis in the mouse, premeiotic cells can be recognized with 2 and 4 times the haploid DNA content. The latter cells proceed directly into leptotene, and the subsequent maturation divisions divide the DNA into haploid spermatids. It is thus evident that all the DNA required for 4 spermatids is present in the premeiotic nuclei before meiosis. The implications of the findings are discussed. It is concluded that the data are best interpreted by considering DNA as an integral component of the gene.