Purpose: The present study was conducted to investigate the expression and possible role of the c-myc protooncogene in preimplantation embryos by using reverse-transcriptase/polymerase chain reaction (RT-PCR) technique and microinjection of synthetic antisense c-myc oligonucleotide probe, respectively. Total RNA was extracted from oocytes and two cell-, four cell-, early morula-, late morula-, early blastocyst-, and late blastocyst-stage embryos, and cDNA was constructed using MMLV reverse transcriptase. Sense primer (P1) and antisense primer (P2) used were based on the c-myc gene sequence bp 1609-1629 and bp 3279-3299, respectively, that span a 1.37-kb intron. PCR-amplified products of cDNA from oocyte-, two cell-, four cell-, early and late morula-, and blastocyst-stage embryos demonstrated the expected 313-bp product in Southern blot hybridization using a c-myc specific DNA probe, with an indication of lower levels in oocytes and early morulae.
Results: Cytoplasmic injection of the antisense c-myc oligonucleotide probe (P2) and not the sense probe (P1) into pronuclear-stage zygotes caused a significant (P = 0.02 to 0.0001) inhibition of development to blastocysts in a concentration-dependent manner, with a maximal inhibition at the first cleavage of zygotes to two cell-stage embryos. There was no effect on the P2 antisense injection on pronucleus formation.
Conclusion: These results indicate that the c-myc protooncogene is expressed in preimplantation embryos and may have an essential role in normal embryogenesis in mice.