mRNA sequence diversity during early embryogenesis in Drosophila melanogaster

The poly A⁺ RNA sequence complexity of stage 14 oocytes of Drosophila melanogaster was determined using hybridization kinetics. Poly A⁺ RNA from this stage served as a template for making cDNA with AMV reverse transcriptase. RNA and its complementary DNA were then allowed to hybridize, the extent of hybridization with time serving as an estimate of complexity. The RNA complement of a stage 14 oocyte falls into three frequency classes: 22% is represented by 102 different sequences, each present an average of 1.8 × 10⁷ times; 28% is represented by 2877 sequences, each present an average of 8.0 × 10⁵ times; and 18% is represented by 11510 sequences, each present 1.2 × 10⁵ times. Changes in the temporal diversity of the sequence complexity between the stage 14 oocyte, 3 1 2 h embryo (gastrula) and 17 1 2 h embryo (late embryogenesis) were then examined. The results indicate that 2.5% of the sequences present in the oocyte have disappeared by 3 1 2 h and 5.3% by 17 1 2 h. 7.7% of the sequences present at 3 1 2 h were not present in the oocyte while 11% of the 17 1 2 h sequences were not present at stage 14. The overall results indicate that temporal poly A⁺ RNA diversity does occur in Drosophila, but that the majority of sequences are retained throughout early embryogenesis.