Spatial changes in poly(A) concentrations during early embryogenesis in Xenopus laevis: analysis by in situ...

The dorsal-ventral axis of the Xenopus embryo is approximately determined by the point of sperm entry, which occurs randomly about the animal-vegetal axis of the egg. Two cytoplasmic components were studied whose spatial arrangements and local concentration patterns appear to reflect the forming dorsal-ventral axis. First, three-dimensional maps depicting the rearrangements of different size classes of yolk platelets were reconstructed from serial sections. These maps provide information on the time when movements occur and the intracellular directions and distances components can travel within the early embryo. Second, local poly(A) concentrations were observed using a [3H]poly(U) in situ hybridization probe. Poly(A) concentrations were observed to change reproducibly from fertilization to late cleavage. Two cytoplasmic areas were found to undergo major, stage-specific increases in poly(A) concentration.