Oocyte Activation Deficiency and Advances to Overcome
This chapter defines oocyte activation and the main molecular events related to this crucial phenomenon which takes place upon sperm-oocyte fusion. Oocytes are arrested at metaphase-II until fertilization and are alleviated from arrest by their interactio
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Oocyte Activation Deficiency and Advances to Overcome Marc Yeste, Celine Jones, Siti Nornadhirah Amdani, and Kevin Coward 34.1
What Is Oocyte Activation? – 430
34.2
The Sperm-Borne Oocyte Activation Factor – 430
34.2.1 34.2.2 34.2.3 34.2.4 34.2.5
T he First Attempts – 430 The Truncated Form of CD117 (TR-KIT) – 430 Cytrate Synthase – 430 Postacrosomal Sheath WW Domain-Binding Protein – 431 Phospholipase Cζ (PLCζ) – 431
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The Sequence of Events During Oocyte Activation – 432
34.4
he Significance of Calcium (Ca2+) Oscillation Patterns T in the Oocyte and Their Role in Controlling the Molecular Mechanisms of Oocyte Activation – 434
34.5
ocyte Activation Deficiency in the Context of Human O Infertility – 435
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Artificial Oocyte Activation – 436
34.6.1 34.6.2 34.6.3 34.6.4 34.6.5
ethods to Activate the Oocyte Artificially – 436 M Artificial Oocyte Activation in Clinical Practice – 437 Is AOA Safe for Child Health? – 437 Is AOA Always Useful for Rescuing Fertility? – 438 Could Recombinant PLCζ Represent an Effective Agent to Rescue OAD? – 439
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Conclusions – 439
Review Questions – 439 References – 439
Authors’ contribution: M.Y. wrote the chapter. C.J., S.N.A. and K.C. critically revised the chapter and approved the final version. © Springer Nature Switzerland AG 2019 Z. P. Nagy et al. (eds.), In Vitro Fertilization, https://doi.org/10.1007/978-3-319-43011-9_34
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Learning Objectives 55 To learn what oocyte activation is and when it does occur 55 To understand the mechanisms underlying oocyte activation and to emphasize the crucial role of a sperm-specific protein, PLCζ 55 To comprehend the relationship between oocyte activation deficiency and human infertility 55 To obtain a global picture of current ART that allows artificial activation of the oocyte
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What Is Oocyte Activation?
Upon ovulation, oocytes have not yet completed the second meiotic division and remain arrested at metaphase II (M-II; see Tripathi et al. [1] for review) until the oocyte is fertilized by a spermatozoon [2, 3]. The process by which the oocyte resumes the second meiotic division is known as “oocyte activation” [4, 5]. During this process, a sperm cell triggers a series of calcium (Ca2+) oscillations within the ooplasm which are involved in crucial events, such as the exocytosis of cortical granules, extrusion of the second polar body, regulation of gene expression, and the initiation of embryogenesis [4, 6, 7]. Although substantial progress has been made over the last decade, the precise mechanism by which the presence of a sperm within the ooplasm triggers the process of oocyte activation remains debatable, and the identity of the sperm factor responsible for this process has been the source of much scrutiny [8]. During the 1980s, three theories were proposed to explain this event (reviewed by Machaty [5]): (1) the “receptor” theory, which proposed that a sperm ligand interacted with a receptor situated on the oocyte plasma membrane and that the oocy
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