Transient Expression of a Translation Initiation Factor Is Conservatively Associated with Embryonic Gene Activation in Murine and Bovine Embryos¹

^a Departments of Obstetrics and Gynaecology and Physiology, University of Western Ontario, London,Ontario, Canada N6A 5C1 ^b Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104–6018

In the present study the abundance of mRNAs for eukaryotic translation initiation factors eIF-1A (formerly known as eIF-4C), -2, -4A, -4E, and -5 was examined in in vivo-derived mouse embryos throughout preimplantation development using a semiquantitative reverse transcription-polymerase chain reaction assay. Although the mRNA profile for each gene is unique, only mRNA for eIF-1A transiently increases during embryonic gene activation (EGA) at the 2-cell stage, and this was confirmed by an independent hybridization-based assay. In in vitro-developed bovine embryos, mRNA for eIF-1A was transiently detected at the 8-cell stage, when the major activation of the genome occurs in this species. As in the mouse, detection in 8-cell bovine embryos was sensitive to the transcriptional inhibitor -amanitin. It was also observed at the same time relative to cleavage in embryos cultured in defined medium under a reduced oxygen environment, and in medium supplemented with serum and somatic cells in 5% CO₂ in air. Neither the chronology of early cleavage divisions nor the yield of bovine blastocysts differed in these culture media. Our results suggest that transient expression of eIF-1A in the mouse and cow is a conserved pattern of gene expression associated with EGA in mammals.

¹ This research was support by an operating grant from the Medical Research Council of Canada (MT-12711) to A.J.W. and a grant from the NIH (HD 22681) to R.M.S. P.A.D. was supported by an NSERC postdoctoral fellowship from Canada during his tenure in the RMS laboratory and was supported by a Organon postdoctoral fellowship in reproductive biology, in the laboratory of A.J.W. A.J.W. is a scholar of the MRC of Canada.

² Correspondence: Richard Schultz, Department of Biology, University of Pennsylvania, 415 South University Ave., Philadelphia, PA 19104-6018. FAX: 215 898-8780; rschultz{at}sas.upenn.edu

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