Viable Human Embryos Research Articles

Oocyte maturation and embryonic failure.

Embryonic development is readily compromised by imperfections introduced during the process of oocyte maturation. We discuss the nature and causes of these imperfections, particularly in oocytes exposed to inappropriate hormonal regimes in vivo or to culture systems designed to induce the maturation of oocytes in vitro. The acquisition of developmental competence involves the synthesis and storage of a wide range of molecules during oocyte growth followed by the reprogramming and ordered utilization of these stored products during maturation, fertilization and early embryogenesis. The regulatory signals for these molecular changes are produced by the follicle cells in response to circulating levels of gonadotrophins; we report that some ovarian stimulation protocols distort these signals thereby disrupting molecular reprogramming of the oocyte and reducing subsequent developmental competence. The aspiration of immature oocytes from antral follicles followed by their maturation in vitro is a potential alternative to hormonal stimulation of patients in IVF treatment. Although relatively successful in a variety of animals, the production of fully viable human embryos by in-vitro maturation is still unsatisfactory despite the use of a wide variety of culture protocols. Our data suggests that the key to maturation and embryo viability in vitro resides in the follicle cell compartment rather than the oocyte. Because of rapid luteinization changes, follicle cells in culture probably fail to provide the maturing oocyte with the necessary ordered set of instructive signals and nutrients needed for the acquisition of developmental competence. Although much remains to be discovered about the nature, concentration and transmission of signals, nevertheless it is already clear that different steroids, matrix metalloproteinases and growth factors are involved in conferring viability on the maturing oocyte. Major improvements in the yield of viable embryos from in-vitro matured oocytes can be anticipated from a systematic analysis of somatic signals from the pre-ovulatory follicle.

Spermatid injection into human oocytes. I. Laboratory techniques and special features of zygote development

Spermatid injection into the oocyte cytoplasm has been shown recently to yield viable human embryos developing to term after transfer to the mother. This study provides details of the laboratory techniques related to round spermatid injection (ROSI) and elongated spermatid injection (ELSI) and focuses on some special features of zygote development associated with the use of these types of sperm precursor cells for fertilization. A spermatid-enriched fraction was obtained by centrifugation of cells from azoospermic ejaculates through a discontinuous Percoll gradient column. Individual round or elongated spermatids were identified in this fraction and injected deep into oocytes. Oocyte activation was boosted by a vigorous aspiration of the ooplasm at the time of injection. The fertilization rates after ROSI and ELSI were 45 and 44% respectively. A single large syngamy nucleus was detected in 36% of the zygotes that previously showed two normal-sized pronuclei. This condition did not appear to delay the first cleavage division. These observations underscore the importance of distinguishing the syngamy nucleus of diploid zygotes from the female pronucleus of haploid, parthenogenetically activated eggs.