| Abstract: | Mouse 70-kDa heat shock proteins Hsp70–1 and Hsp70–3 (Hsp70–1/3) are stress-inducible protein chaperones thought to protect embryonic cells and tissues from the effects of a wide range of environmental exposures. Hsp70–1/3 are expressed constitutively, and at times are stress-inducible during various stages of preimplantation embryogenesis. In order to elucidate the functions of constitutive and stress-inducible Hsp70 expression in mouse preimplantation embryos, the consequences of inhibiting expression with antisense oligonucleotides complementary to the mRNAs of hsp70–1 and hsp70–3 (AO70–1/3) were evaluated. Transfection of preimplantation embryos (four-cell stage) with 2.5 μM AO70–1/3 had no effect on in vitro blastocoel formation. However, transfection with 5 or 10 μM AO70–1/3 reduced in vitro blastocyst development to 30% and 0%, respectively (approximately 90% control embryos developed to blastocyst). Thus constitutive expression of Hsp70–1/3 appears significant to preimplantation embryogenesis. Limiting expression of Hsp70–1/3 with 5 μM AO70–1/3 also heightened embryo sensitivity to arsenic, resulting in less than 5% in vitro development to blastocyst in the presence of the subtoxic dose of 0.4 μM sodium arsenite. Whether the combined effect of AO70–1/3 and arsenic is due to blocking inducible expression of the Hsp70s, or due to further reducing the amount of constitutively expressed Hsp70s available to the embryo is not known at this time. However, these results clearly indicate that some minimal amount of Hsp70–1 and/or Hsp70–3 is required for preimplantation embryogenesis, and that increasing the demand for Hsp70s by arsenic exposure heightens this requirement. Mol. Reprod. Dev. 51:373–380, 1998. © 1998 Wiley-Liss, Inc. |
