Emission of Feulgen-positive Particles during the in vitro Maturation of Toad Ovocytes

Abstract

THERE has recently been a growing interest in the possible role and localization of cytoplasmic deoxyribonucleic acids (DNA) in amphibian eggs. Our own observations^1–3 suggest that large amphibian ovocytes contain at least two different kinds of DNA: a major constituent, which is bound to the yolk platelets and is probably a reserve material of low molecular weight, and a minor component which surrounds the germinal vesicle of the larger ovocytes: the latter is relatively resistant to acid hydrolysis and might originate from the nuclear sap which, as shown by Izawa et al.⁴, contains appreciable amounts of DNA. It is of interest to examine the distribution of DNA in ovocytes which, as a result of a treatment with pituitary hormones, undergo maturation (breakdown of the germmal vesicle which results in the mixing of the nuclear sap and the cytoplasm). In fact, some 25 years ago, I examined³ DNA distribution during the spontaneous maturation of frog (Rana temporaria) ovocytes: it was observed that the breakdown of the germinal vesicle is followed by the appearance of small Feulgen-positive granules which lie close to the chromosomes. Their origin and fate could not be established.