Decreased expression of mitochondrial genes in human unfertilized oocytes and arrested embryos

Objective To evaluate the relationship between mitochondrial gene expression of oocytes/embryos and their fertilizability in unfertilized oocytes, arrested embryos, and tripronucleate zygotes, because both nuclear and cytoplasmic factors contribute to oocyte activation, fertilization, and subsequent development. Design Prospective laboratory research. Setting In vitro fertilization (IVF) laboratory in a university hospital. Patient(s) Seventy-five unfertilized oocytes, 45 arrested embryos, and 24 tripronucleate (3PN) embryos from 45 female patients undergoing IVF. Intervention(s) Analysis of mitochondrial gene expression by semiquantitative reverse transcription polymerase chain reaction (RT-PCR). Main outcome measure(s) Comparison of the expression levels of mitochondrial genes including ND2, CO I, CO II, ATPase 6, CO III, ND3, ND6, and Cyt b in three groups. Result(s) Significantly decreased transcription levels were expressed in unfertilized oocytes and arrested embryos. The average expression levels of the eight determined genes compared with the control (GAPDH) was 4.4 ± 0.7, 6.4 ± 1.1, and 13.2 ± 1.1 in unfertilized oocytes, arrested embryos, and 3PN embryos, respectively. Significantly decreased expressions of the ATPase 6, CO III, and ND3 genes were detected from samples with 4977-bp common deletion in the mitochondrial DNA (mtDNA) compared with the non-deletion group. Conclusion(s) The present study is the first report to present globally decreased mitochondrial gene expression levels in human compromised oocytes and embryos. These data support the notion that the down-regulation of mitochondrial RNA by defective oxidative phosphorylation genes possibly affects oocyte quality including fertilization and further embryo development.