Utilization of maternal and embryonic histone RNA in early sea urchin development

Histone RNA in early sea urchin embryos is derived from maternal stores and from new transcription. We show that the sedimentation of maternal free RNPs, containing histone RNA, is somewhat more rapid than the sedimentation of the newly made histone RNPs. Yet, prior to the 2- to 4-cell stage, both the maternally derived and the newly synthesized histone RNA are localized to the same extent in the non-polysomal-free RNPs, and the timing of their recruitment into embryonic polysomes appears to be the same. The levels of hybridization of histone probe to RNAs in cleaving embryos increases severalfold in intensity, and the increase occurs primarily in the polysomes. These data suggest that new transcription may provide an important contribution to the total histone RNA mass by as early as the 32- to 64-cell stage of development.