INHIBITION OF HSP70-1 AND HSP70-3 EXPRESSION DISRUPTS PREIMPLANTATIONEMBRYOGENESIS AND HEIGHTENS EMBRYO SENSITIVITY TO ARSENIC

Mouse 70-kDa heat shock proteins Hsp70-1 and Hsp70-3 (Hsp70-1/3) are s tress-inducible protein chaperones thought to protect embryonic cells and tissues from the effects of a wide range of environmental exposure s. Hsp70-1/3 are expressed constitutively, and at times are stress-ind ucible during various stages of preimplantation embryogenesis. In orde r to elucidate the functions of constitutive and stress-inducible Hsp7 0 expression in mouse preimplantation embryos, the consequences of inh ibiting expression with antisense oligonucleotides complementary to th e mRNAs of hsp70-1 and hsp70-3 (A070-1/3) were evaluated. Transfection of preimplantation embryos (four-cell stage) with 2.5 mu M A070-1/3 h ad no effect on in vitro blastocoel formation. However, transfection w ith 5 or 10 mu M A070-1/3 reduced in vitro blastocyst development to 3 0% and 0%, respectively (approximately 90% control embryos developed t o blastocyst). Thus constitutive expression of Hsp70-1/3 appears signi ficant to preimplantation embryogenesis. Limiting expression of Hsp70- 1/3 with 5 mu M A070-1/3 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 mu M sodium arsenite. Whether the combined effect of A070-1/3 and arsenic is due to blocking inducible expression of the Hsp70s, or due to further reducing the amount of con stitutively expressed Hsp70s available to the embryo is not known at t his time. However, these results clearly indicate that some minimal am ount of Hsp70-1 and/or Hsp70-3 is required for preimplantation embryog enesis, and that increasing the demand for Hsp70s by arsenic exposure heightens this requirement. Mel. Reprod. Dev. 51:373-380, 1998. (C) 19 98 Wiley-Liss, Inc.dagger.