During oogenesis, substances are synthesized, stored in the oocyte and after fertilization act to control early development. Those substances (morphogenetic determinants) are distributed in a pattern in the cytoplasm of the fertilized egg. That pattern reflects the areas where the major organ/tissue systems of the embryo will eventually form. The embryonic body axis, future mesoderm (muscle) and neural (brain and spinal cord) development, results from such cytoplasmic localizations. The research described in this proposal shows for the first time that: (1) The potential for body axis development is established by the 32-cell stage of Xenopus embryogenesis. This occurs before expression of the embryonic genome and is therefore under the control of substances produced during oogenesis. (2) Isolated animal pole octets only form a ciliated ectodermal vesicle in culture, however injection of oocyte RNA into one or two cells of the octet results in formation of an """"""""embryo"""""""" with some mesodermal and neural structures, such as notochord, striated muscle, nephric ducts, melanocytes, neural tube and eyes. (3) This ability to cause formation of mesodermal and neural structures appears to be primarily associated with oocyte poly (A+) RNA. Activity is found in certain sucrose gradient fractions of the poly (A+) RNA and segregates with size classes smaller than 18s rRNA. (4) This appears to be a unique property of oocyte RNA, since other RNAs (ie: tadpole poly (A+) RNA, adult liver RNA or yeast tRNA) do not show the ability to elicit development of mesodermal or neural structures when microinjected into the isolated animal pole octet. We propose experiments to isolate and characterize this oogenetically synthesized RNA. These experiments will provide a very powerful tool for understanding the factors involved in the formation of the neural/axial system of vertebrates.
| Pierce, K E; Brothers, A J (1992) The marginal zone of the 32-cell amphibian embryo contains all the information required for chordamesoderm development. J Exp Zool 262:40-50 |
