The synthesis of RNA containing polyadenylic acid sequences in preimplantation mouse embryos

In mammalian embryonic development, RNA synthesis commences quite early, e.g. in the mouse, RNA synthesis is detectable by the 2-cell stage (reviewed by Epstein, 1975). The types of RNA synthesized by preimplantation mouse embryos at various stages of development have been studied by Ellem & Gwatkin (1968), who used methylated albumin Kieselguhr (MAK) chromatography, by Pikó (1970), who used sucrose gradient centrifugation, and by Warner & Hearn (1977), who worked with polyacrylamide gel electrophoresis. All of these studies are in excellent qualitative agreement, showing that, from the 8-cell stage and continuing through the blastocyst stage, all classes of RNA are synthesized. The predominant class synthesized is rRNA, and the distribution of newly synthesized RNA among the different nucleic acid classes is similar for 8-cell and blastocyst embryos. However, none of these studies has unequivocally identified HnRNA or mRNA, both of which are presumably being synthesized by the embryos.