Factors Influencing the Biochemical Markers for Predicting Mammalian Oocyte Quality

Abstract

Abstract. The need for accurate selection of the best oocytes for in vitro fertilization protocols and thus, production of embryos has driven the search for oocyte quality markers from morphological criteria to biochemical parameters. Current studies are focused on the biochemical constituents of the follicular fluid and gene expression profiling of the cumulus cells. These parameters are, however, affected by factors that must be considered before making a judgment of the oocyte's quality. These includes factors such as the type of hormonal stimulation protocol, age of oocyte donor and heat stress on the donor, all of which have been reported to influence the concentrations of many hormones, apolipoproteins, metabolites, fatty acids and growth factors in the follicular fluid and the expression of several genes in the cumulus cells. Another important point to note is species variation in the response to these extraneous influences, which thus calls for species targeted investigations. As reports are still scanty and investigations assumed to be very keen, we employed this review paper to bring attention of researchers and clinicians to those factors that may come to bear on the outcome of their investigations on oocyte and embryo quality. Key words: Cumulus cells, Follicular fluid, Mammalian oocytes, Quality prediction (J. Reprod. Dev. 58: [385][386][387][388][389][390][391][392] 2012) I t is well known that only part of the in vivo ovulated oocytes and in vitro matured oocytes are capable of developing to viable embryos after fertilization. This led to the search for a reliable indicator of oocyte quality. Thus, one of the important puzzles for reproductive biologists today is the search for a reliable noninvasive marker of the quality of oocytes for both human and animal assisted reproduction.Initial attempts at evaluating the quality of oocytes meant for in vitro fertilization (IVF) focused on the physical/morphological characteristics of the Cumulus-oocyte-complexes (COCs) [1,2]. These criteria are both noninvasive and rapid and are still generally in use today. However, recent reports on the inadequacies of a simple morphological appearance as a measure of quality suggest that morphological markers cannot be completely relied upon [3,4]. This has led to intensification of the search for alternative or complementary criteria with focus on the follicular fluid (FF) and the cumulus cells (CCs) around the oocyte.The preovulatory oocyte communicates intimately and directly with the surrounding cumulus granulosa cells through specialized transzonal cytoplasmic projections [5] and with the more distant mural granulosa cells through the follicular fluid [6]. Many biochemical substances found in these close associates of the oocyte have been studied and correlated with the developmental competence of the oocyte. Very recent attempts are even looking beyond a single substance to the totality of the biochemical constituents of the follicular fluid. This area of research is referred to as metabolomics [7]. Revelli e...

Metabolic control of oocyte development: linking maternal nutrition and reproductive outcomes

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