Morphological variability and its physiological origin in oocyte nuclei of the crested newt

Abstract

ABSTRACT The effects of hypophysectomy and of subcutaneous injection of gonadotrophin upon whole oocytes, oocyte nuclei, and lampbrush chromosomes of the newt Triturus cristatus carnifex have been studied. Hypophysectomy leads to a reduced rate of incorporation of 32P into the whole oocytes and oocyte nuclei. Large, yolky oocytes are more severely affected than are small oocytes lacking yolk. Hypophysectomy also leads to decreased stiffness of oocyte nuclear sap, change in the number and character of free granules in the nuclear sap, and alteration in the size of certain objects occurring at specific sites on the lampbrush chromosomes. Injection of mammalian gonadotrophin leads to an increased rate of uptake of 3aP into the cytoplasm and nuclei of yolky oocytes. Gonadotrophin treatment also leads to increased stiffness of oocyte nuclear sap, decrease in the number and/or the size of free granules in the nuclear sap, reduction in size of the giant loops of chromosomes X, XI, and XII, and changes at the axial granule loci of chromosome I and the sphere loci of chromosomes V and VIII. Each of the features mentioned above varies in nature from one animal to another. This inconstancy, which is superimposed upon stable genetic characteristics and upon those developmental changes which normally accompany oocyte growth, is now shown to reflect differences in the physiological states of the ovaries of different newts.