Cytological analysis of nuclear migration and dissolution during steroid‐induced meiotic maturation in vitro of follicle‐enclosed oocytes of the goldfish (<i>Carassius auratus</i>)

Abstract

Abstract The effect of progestogens on nuclear or germinal vesicle dissolution (GVD) was tested in goldfish (Carassius auratus) follicle‐enclosed oocytes in vitro. The results indicated the following hierarchy of GVD activity: 17α20β dihydroxy progesterone (DHP) &gt; 17α hydroxy progesterone (HP) &gt; progesterone (P). Further studies with DHP indicated that nuclear migration (GVM) preceded GVD, and that no significant GV size changes (ie, diameter in animal‐vegetal pole axis) occurred during GVM. The in situ GV visualization technique used (ie, acetic acid yolk clearing with concurrent nuclear precipitation) was verified using standard paraffin sectioning procedures. The two techniques yielded highly correlated results and indicated that GVM is initiated between 12–18 hr, after DHP addition at 15°C. The goldfish oocyte in vitro system as described here is a useful model for the study of hormonally induced GVM and GVD.