28 EFFECT OF TREATMENT OF OVINE OOCYTES WITH CAFFEINE ON GENE EXPRESSION IN NUCLEAR TRANSFER EMBRYOS

Abstract

The efficiency of animal production by somatic cell nuclear transfer (SCNT) remains low and this has been linked to incomplete epigenetic reprogramming of the donor somatic cell nucleus. Previous studies have reported that embryos produced by SCNT exhibit abnormal expression patterns for a number of genes, including IL6, FGF4, FGFr2, Hsp, IF-tau, DNMT, and Mash2 (Daniels et al. 2000 Biol. Reprod. 63, 1034-1040; Wrenzycki et al. 2001 Biol. Reprod. 65, 309-317). Recently, we demonstrated that treatment of telophase I or metaphase II ovine oocytes with 10 mM caffeine for 6 h increased the activities of both MPF and MAPK kinases. In NT embryos produced using caffeine treated oocytes as recipient cytoplasts, no increase in the frequency of development to the blastocyst stage was observed; however, blastocyst stage embryos had an increased cell number (Lee and Campbell 2005 Reprod. Fertil. Dev. 16, 125). The objective of the present study was to examine the effects of caffeine treatment on the expression levels of a number of genes involved in early development. Target genes were categorized into seven groups based on their function: (1) transcription factors (Oct-4, Sox-2), (2) growth factors (IGF-1, IGF-1r, IGF-2r, FGF-2, and FGF-4), (3) stress adaptation (Hsp70.1 and Hsp27), (4) metabolism (Glut-1, Glut-3, and Glut-4), (5) compaction/cavitation (DcII), (6) trophoblastic function (IF-tau), and (7) nuclear reprogramming factors (Hist4h4, H2A.Z, and Lmna). To determine the transcript levels semiquantitatively, different PCR cycle parameters were used (35 and 40 cycles). Expression levels were compared in blastocyst-stage embryos obtained from five groups produced as previously described (Lee and Campbell 2005; Maalouf et al. 2005 Reproduction 32, 49): (I) IVF embryos, (II) caffeine-treated IVF embryos, (III) parthenotes, (IV) SCNT embryos, and (V) caffeine treated SCNT embryos. No differences in overall expression patterns were observed among groups I, II, and III. In group IV non-treated SCNT-derived embryos, an aberrant gene expression pattern was found with respect to Oct-4 and genes regulated by Oct-4: H2A.Z, IF-tau, and FGF-4, Oct-4, H2A.Z, and FGF-4 were down-regulated and IF-tau was up-regulated. In contrast, the expression patterns of group V caffeine-treated SCNT embryos resembled those of control groups I, II, and III. In comparison to gene expression in group IV embryos, Oct-4, FGF-4, and H2A.Z were up-regulated but IF-tau was down-regulated. Previous studies have demonstrated that FGF-4 and H2A.Z play an important role in early development and implantation, whereas expression of IF-tau is related to embryo quality (Feldman et al. 1995 Science 267, 246-249; Fasst et al. 2001 Curr. Biol. 11, 1183-1187; Wrenzycki et al. 2001). Our results demonstrate that treatment of oocytes with caffeine prior to embryo reconstruction can alter the expression patterns of developmentally regulated genes in SCNT embryos to more closely resemble those of IVF controls.