Amounts, synthesis, and some properties of intracisternal A particle-related RNA in early mouse embryos

Abstract

Early mouse embryos express two morphological subtypes of intracisternal A-type particles, one resembling those occurring in mouse tumors (referred to as IAP) and the other apparently specific for early embryos [referred to as IAP(ε)]. Using cloned fragments of IAP genes as labeled probes in dot-hybridization experiments, we detected IAP-related RNA sequences in mouse oocytes and preimplantation embryos. IAP RNA is relatively abundant in ovarian oocytes, is reduced in amount to ≈1/10th in the ovulated egg, and increases ≈100 times (from ≈1.3x10^(3) to ≈1.5x10^(5) molecules per embryo) between the one-cell stage and late blastocyst stage. Most of the IAP RNA consists of a single size class of about 5.4 kilobases, and a major fraction of this RNA is polyadenylylated. Quantitative considerations suggest that only a few percent of the IAP RNA in embryos are associated with particles. In two-cell embryos, the number of IAP RNA molecules is <1/10th the number of IAP(ε) particles, suggesting that IAP(ε) is genetically distinct from IAP and presumably represents a family of as yet unidentified retrovirus-like elements.

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