Guardians of Oocyte Quality


Oocyte quality is fundamental to assisted reproduction, agricultural livestock productivity and species preservation. Mammalian oocytes develop in close coordination with somatic follicle cells of the ovary, and manifest remarkable molecular mechanisms that serve as guardians of oocyte quality and integrity. Genome and mitochondrial integrity are major aspects of oocyte quality determination. Ongoing research is revealing the details of these mechanisms, and how they help protect oocytes from detrimental effects of exogenous factors.

Key Concepts

  • Oocyte quality is essential for assisted reproduction success.
  • Development of the oocyte involves an intricate set of bidirectional signals between the oocyte, cumulus cells and follicular fluid components, which can impact the quality of the oocyte.
  • Chromosome segregation and adaptability to DNA damage are critical for the integrity of oocyte's genome.
  • Energy production, proper distribution of mitochondria and regulation of fusion/fission are essential for maintaining the integrity of the mitochondria and oocyte developmental competence.
  • Overall, oocyte maturation and development is a highly regulated process, and disruption in this process could comprise the mitochondrial and genomic integrity, further impacting the health of the oocytes.
  • There are a variety of extrinsic factors, such as maternal health, maternal diet and environmental exposures, that can further impact oocyte quality.
  • Therapies such as antioxidant, melatonin, CoQ10 and resveratrol treatments have been suggested to improve oocyte quality, but more studies are needed to determine efficacy.
  • Novel biomarkers of oocyte quality need to be discovered.

Keywords: mitochondria; genome; spindle; metabolic disorders; therapies

Figure 1. Schematic diagram of stages of ovarian folliculogenesis and associated cell types. Oocytes become associated with granulosa cells, which proliferate as the oocyte grows. The developing follicle becomes surrounded by thecal cells and a basal lamina. During formation of tertiary follicle, granulosa cells diverge into two specialised cell types: cumulus and mural granulosa cells. The cumulus oophorus cells contact the oocyte through the zona pellucida and establish gap junctions. A complex dialogue between the oocyte and somatic cells supports oogenesis. Mitochondria undergo complex changes during oogenesis as well.
Figure 2. Major processes determining mammalian oocyte quality. An intricate set of bidirectional signals between oocyte and associated cumulus cells, granulosa cells and follicular fluid components (black arrows) drive successful production of high‐quality oocytes. Molecular mechanisms exist to maintain genomic and mitochondrial integrity during oogenesis and in matured oocytes, including mechanisms that ensure DNA damage repair, correct chromosome congression and segregation, mitochondrial fusion and fission, mitochondrial redistribution and control of reactive oxygen species production (purple arrows). Environmental factors such as maternal disease, age and toxins can impact these mechanisms and reduce oocyte quality (red arrows). Antioxidants and nutritional supplements are being considered as possible tools for rescuing and maintaining oocyte quality (green arrows).


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Further Reading

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Ruebel, Meghan L, and Latham, Keith E(Jun 2018) Guardians of Oocyte Quality. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0027925]