KINETIC ANALYSIS OF ENTIRE OOGENESIS IN XENOPUS LAEVIS

In our breeding conditions (without artificial hormonal stimulation) two years after metamorphosis are necessary for a Xenopus laevis female to produce mature oocytes. Four periods of different growth rates can be distinguished into this first wave of oogenesis: 1) oocytes reach 120 μm in diameter (early stage I according to Dumont (5)) in a few weeks after metamorphosis; 2) growth slows down and the size of 250-300 μm (late stage I) is obtained 6-7 months later; 3) a rapid growth resumes during vitellogenesis (stages II, III and IV) and a 1,000-1,100 μm diameter is reached in 2-3 months; 4) the last period spans for a year and the oocyte grows up to 1,200 μm. This phase covers many physiological changes and it should be critical to size carefully the oocytes for biochemical investigations and comparisons. At last most of the oocytes in a young female do not proceed through this entire oogenesis, they are stopped at the end of the second growth phase (about 250 μm in diameter).