Microinjection of mitochondria into zygotes creates a model for studying the inheritance of mitochondrial DNA during preimplantation development

Objective: To determine the effect of mutant mitochondria on preimplantatio n embryo development and of preimplantation embryo development on the survi val of mutant mitochondrial DNA. Design: Laboratory research. Setting: Academic research laboratory. Patient(s): None. Intervention(s): Mutant and wild-type mitochondria, fractionated from tissu e obtained from a patient with MELAS syndrome, a mitochondrial disease, wer e microinjected into mouse zygotes. Control zygotes received either no inje ction or sham injection. Main Outcome Measure(s): Preimplantation embryo development and survival of mutant mitochondrial DNA as determined by polymerase chain reaction analys is. Result(s): After microinjection into zygotes, the MELAS mutation could be i dentified by polymerase chain reaction until the hatched blastocyst stage o f embryo development. The survival of MELAS-injected zygotes, observed for 4 days after injection, did not differ from the survival of zygotes injecte d with wild-type mitochondria or from the survival of uninjected or sham-in jected controls. Conclusion(s): It appears that preimplantation embryo development does not screen out mitochondrial DNA mutations introduced into fertilized oocytes, and low levels of mutant mitochondrial DNA do not disrupt early embryo deve lopment. (C) 1999 by American Society for Reproductive Medicine.