The role of veterinarians in human in vitro embryo production
Braga, Daniela Paes de Almeida FerreiraBorges Junior, Edson
Background: Infertility affects approximately 15% of couples of childbearing age, and there is evidence that fertility has been declining at an accelerated pace in recent years. Recent advances in assisted reproductive technologies (ART) have made biological parenthood possible for couples who previously had no hope of childbearing. On the other hand, the primary use of embryo transfer in cattle has been amplification of the reproductive rates of valuable females. In 2007, 245,257 bovine embryos were produced globally; Brazil accounted for 86.6% of this output. The popularity of this technology has contributed to the growing knowledge of embryology among veterinarians. Because of ethical concerns regarding the use of human subjects, bovines have been used as a model for the study of reproductive biology in women. Therefore, this manuscript will discuss approaches for oocyte selection and sperm selection that were developed in animal models and adapted for ART in humans. Review: One of the most important factors determining the outcome of embryo development is gamete quality. Numerous attempts have been made to identify prognostic factors for oocyte development potential. One promising approach uses spindle imaging as a predictor of oocyte quality. The development of a polarised light microscope that evaluates the birefringence of living cells enabled the evaluation of highly birefringent oocyte spindles without damage to the cell. Polarised light microscopy also enables the evaluation of other birefringent, sub-cellular oocytes structures, such as the zona pellucida. The birefringence of the meiotic spindle and the zona pellucida are valuable tools in predicting the developmental potential of oocytes and embryos. The post-genomic era has facilitated the growth of non-invasive approaches to the study of embryonic physiology and to predicting oocyte developmental competence and viability. These approaches include the assessment of proteomic profiling and, most recently, of the oocyte and embryonic metabolome. Although intracytoplasmic sperm injection ICSI outcomes are apparently unrelated to basic sperm parameters, recent reports have suggested a paternal contribution to the success of embryonic development and implantation, and a new method for sperm evaluation has been proposed. It is now possible to examine the nuclear morphology of spermatozoa at 6600x magnification. This technique has allowed the introduction of a modified ICSI procedure called "intracytoplasmic morphologically selected sperm injection" (IMSI). As a consequence, real-time, detailed morphological sperm examination using motile sperm organelle morphology examination (MSOME) enables the best available spermatozoa to be selected prior to oocyte injection. Recent reports have suggested that normal nuclear morphology, as viewed under high magnification, may be useful for selecting spermatozoa with higher developmental capacity. Conclusion: Studies in animal reproduction have allowed the development of non-invasive methods of evaluating sperm and oocytes prior to their use in ART. Gamete quality biomarkers, once identified, may allow embryos with the highest implantation potential to be selected with greater accuracy. The use of such biomarkers may thus yield an increased chance of pregnancy, which is the primary objective of ART.
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