The accumulation of repetitive and evolutionary conservative RNA during frog embryonic development.

Frog embryo nuclear and cytoplasmic RNA populations, labeled in vivo and in vitro, were hybridized to, filterbound homologous and heterologous DNA. The transcription of homologous (frog) repetitive DNA into nuclear RNA decreases qualitatively during development while the transcription of heterologous (minnow, human) repetitive DNA into nuclear RNA remains relatively constant qualitatively. The diversity of homologous repetitive mRNA increases during development, but there is only a slight change in the diversity of heterologous repetitive mRNA transcripts. There is a marked restriction of transport of the heterologous RNA sequences to the cytoplasm at a later stage of development.