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2016 ; 22
(4
): 420-39
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Gamete activation: basic knowledge and clinical applications
#MMPMID27278231
Tosti E
; Ménézo Y
Hum Reprod Update
2016[Jun]; 22
(4
): 420-39
PMID27278231
show ga
BACKGROUND: The first clues to the process of gamete activation date back to
nearly 60 years ago. The mutual activation of gametes is a crucial event during
fertilization. In the testis and ovaries, spermatozoa and oocytes are in a state
of meiotic and metabolic quiescence and require reciprocal signals in order to
undergo functional changes that lead to competence for fertilization. First, the
oocyte activates sperm by triggering motility, chemoattraction, binding and the
acrosome reaction, culminating with the fusion of the two plasma membranes. At
the end of this cascade of events, collectively known as sperm capacitation,
sperm-induced oocyte activation occurs, generating electrical, morphological and
metabolic modifications in the oocyte. OBJECTIVE AND RATIONALE: The aim of this
review is to provide the current state of knowledge regarding the entire process
of gamete activation in selected specific animal models that have contributed to
our understanding of fertilization in mammals, including humans. Here we describe
in detail the reciprocal induction of the two activation processes, the molecules
involved and the mechanisms of cell interaction and signal transduction that
ultimately result in successful embryo development and creation of a new
individual. SEARCH METHODS: We carried out a literature survey with no
restrictions on publication date (from the early 1950s to March 2016) using
PubMed/Medline, Google Scholar and Web of Knowledge by utilizing common keywords
applied in the field of fertilization and embryo development. We also screened
the complete list of references published in the most recent research articles
and relevant reviews published in English (both animal and human studies) on the
topics investigated. OUTCOMES: Literature on the principal animal models
demonstrates that gamete activation is a pre-requisite for successful
fertilization, and is a process common to all species studied to date. We provide
a detailed description of the dramatic changes in gamete morphology and behavior,
the regulatory molecules triggering gamete activation and the intracellular ions
and second messengers involved in active metabolic pathways in different species.
Recent scientific advances suggest that artificial gamete activation may
represent a novel technique to improve human IVF outcomes, but this approach
requires caution. WIDER IMPLICATIONS: Although controversial, manipulation of
gamete activation represents a promising tool for ameliorating the fertilization
rate in assisted reproductive technologies. A better knowledge of mechanisms that
transform the quiescent oocyte into a pluripotent cell may also provide new
insights for the clinical use of stem cells.
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