Primate models for assisted reproductive technologies.

Although the deliberate creation of human embryos for scientific research is complicated by ethical and practical issues, a detailed understanding of the cellular and molecular events occurring during human fertilization is essential, particularly for understanding infertility. It is clear from cytoskeletal imaging studies of mouse fertilization that this information cannot be extrapolated to humans because of unique differences in centrosomal inheritance. However, the cytoskeletal rearrangements during non-human primate fertilization are very similar to humans, providing a compelling animal model in which to examine sperm--egg interactions. In order to address this key step in primate fertilization and to avoid the complexities in working with fertilized human zygotes, studies are now exploring the molecular foundations of various assisted fertilization techniques in a monkey model. While intracytoplasmic sperm injection with ejaculated or testicular sperm is quite successful in primate models, there are some specific differences when compared with standard IVF that warrant further investigation, particularly in regards to nuclear remodeling, genomic imprinting, Y-chromosome deletions and developmental outcomes. Similarly, primate models have been useful for examining spermatid function during fertilization but these have met with limited success. One area of primate reproductive research that has yet to be mastered is reproductive cloning. Genetically identical primates would provide the ultimate approach for accelerating stem cell-based therapies for a number of neurodegenerative diseases such as Alzheimer's and Parkinson's disease, as well as targeted gene therapies for various metabolic disorders.