A gradient of poly(A)+ RNA sequences in Xenopus laevis eggs and embryos

Xenopus laevis eggs and gastrula stage embryos were fractionated into three equal sections normal to the animal-vegetal axis, and poly(A)⁺ RNA was isolated from each section. Hybridization of these poly(A)⁺ RNAs with [³²P]cDNA synthesized using animal or vegetal poly(A)⁺ RNAs showed no detectable differences in the extents or rates of reaction. Thus, the vast majority of poly(A)⁺ RNAs are not segregated along the animal-vegetal axis. To increase the sensitivity of these experiments, [³²P]cDNAs were prepared which had reduced levels of RNA sequences from the animal region of the gastrula stage embryo or spawned unfertilized egg. Hybridization reactions with these probes showed that 3 to 5% of the input cDNA represents poly(A)⁺ RNA sequences enriched 2- to 20-fold in the vegetal region of the egg or gastrula stage embryo.