Human Reproduction Update Advance Access originally published online on January 5, 2008
Human Reproduction Update 2008 14(2):159-177; doi:10.1093/humupd/dmm040
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Oocyte-secreted factors: regulators of cumulus cell function and oocyte quality
Research Centre for Reproductive Health, School of Paediatrics and Reproductive Health, Discipline of Obstetrics and Gynaecology, Medical School, University of Adelaide, Adelaide 5005, Australia
1 Correspondence address. Fax: +61-8-8303-8177; E-mail: robert.gilchrist{at}adelaide.edu.au
Oocyte quality is a key limiting factor in female fertility, yet we have a poor understanding of what constitutes oocyte quality or the mechanisms governing it. The ovarian follicular microenvironment and maternal signals, mediated primarily through granulosa cells (GCs) and cumulus cells (CCs), are responsible for nurturing oocyte growth, development and the gradual acquisition of oocyte developmental competence. However, oocyte–GC/CC communication is bidirectional with the oocyte secreting potent growth factors that act locally to direct the differentiation and function of CCs. Two important oocyte-secreted factors (OSFs) are growth-differentiation factor 9 and bone morphogenetic protein 15, which activate signaling pathways in CCs to regulate key genes and cellular processes required for CC differentiation and for CCs to maintain their distinctive phenotype. Hence, oocytes appear to tightly control their neighboring somatic cells, directing them to perform functions required for appropriate development of the oocyte. This oocyte–CC regulatory loop and the capacity of oocytes to regulate their own microenvironment by OSFs may constitute important components of oocyte quality. In support of this notion, it has recently been demonstrated that supplementing oocyte in vitro maturation (IVM) media with exogenous OSFs improves oocyte developmental potential, as evidenced by enhanced pre- and post-implantation embryo development. This new perspective on oocyte–CC interactions is improving our knowledge of the processes regulating oocyte quality, which is likely to have a number of applications, including improving the efficiency of clinical IVM and thereby providing new options for the treatment of infertility.
Key words: oocyte quality / oocyte-secreted factors / oocyte–cumulus cell communication / growth-differentiation factor 9 / bone morphogenetic protein 15
Received on May 30, 2007; revised September 25, 2007; accepted on October 25, 2007