RESUMO
The development of quail embryos obtained after in vitro fertilization of oocytes ovulated in vitro was investigated. About 40% of the specimens, after 18-20 hr of incubation, had undergone cleavage to reach stages IV-VI when viewed under a stereo microscope. However, only 36% of these embryos contained normal, DAPI-stained nuclei when observed under a fluorescent microscope; the other 64% showing a morphologically normal cleavage pattern did not contain nuclei. Control unfertilized oocytes, ovulated in vitro and cultured for the same time, also sometimes attained the morphologically correct stages IV-VI but their "blastomeres" were always devoid of nuclei. Therefore, it is advisable to monitor early avian embryos for the presence of nuclei when assessing development in culture. The results demonstrate, for the first time, that cytoplasmic segmentation can occur in the absence of nuclear divisions in the germinal disc of the quail and show the existence and significance of ooplasmic maternal information in birds. This phenomenon is also known for sea urchin and frogs. It is indicative of the role of maternal information in early development. The in vitro method presented here links the steps of ovulation and fertilization with the early cleavage stages under in vitro conditions and may be useful in studying mechanisms of fertilization and differentiation in birds as well as in obtaining transgenic birds by DNA injection or application of foreign, DNA-carrying sperm.
