Calcium ion currents mediating oocyte maturation events
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BioMed Central
Open Access
Review
Calcium ion currents mediating oocyte maturation events Elisabetta Tosti* Address: Cell Biology Laboratory, Stazione Zoologica, Naples, Italy Email: Elisabetta Tosti* - [email protected] * Corresponding author
Published: 09 May 2006 Reproductive Biology and Endocrinology 2006, 4:26
doi:10.1186/1477-7827-4-26
Received: 18 February 2006 Accepted: 09 May 2006
This article is available from: http://www.rbej.com/content/4/1/26 © 2006 Tosti; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract During maturation, the last phase of oogenesis, the oocyte undergoes several changes which prepare it to be ovulated and fertilized. Immature oocytes are arrested in the first meiotic process prophase, that is morphologically identified by a germinal vesicle. The removal of the first meiotic block marks the initiation of maturation. Although a large number of molecules are involved in complex sequences of events, there is evidence that a calcium increase plays a pivotal role in meiosis re-initiation. It is well established that, during this process, calcium is released from the intracellular stores, whereas less is known on the role of external calcium entering the cell through the plasma membrane ion channels. This review is focused on the functional role of calcium currents during oocyte maturation in all the species, from invertebrates to mammals. The emerging role of specific L-type calcium channels will be discussed.
Review Oocyte maturation Oogenesis is characterized by a unique process of cell division occurring only in gametes, called meiosis; whose goal is the production of haploid cells highly specialized for fertilization. In the majority of species the oocyte arrests in different stages of meiotic division, in particular, the block occurring in the first meiotic prophase (PI) marks the state of immature oocyte characterized by a prominent nucleus called the germinal vesicle (GV), which contains de-condensed transcriptionally active chromatin [[1] for a review]. As a general scheme, in response to a stimulus, meiosis is resumed and manifested by a germinal vesicle breakdown (GVBD), it then progresses to metaphase I (MI) or II (MII) where it undergoes a second arrest that is removed after successful fertilization.
Oocyte maturation is usually defined as the period of progression from the first to the second meiotic arrest and involves coordinated nuclear and cytoplasmic modifica-
tions [2]. These are highly complex processes and their interplay is regulated by a series of sequential molecular events. Nuclear maturation starts with the GVBD, ends at the meiosis exit, and is marked by the presence of the two polar bodies. Cytoplasmic maturation is a more obscure process and involves both morphological and functional alterations rel
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