Abstract:
Participation of major endocrine and/or local autocrine/paracrine factors and potential interplay between
apparently disparate intra-oocyte signalling events during maintenance and withdrawal of meiotic prophase
arrest has been an area of active research in recent years. Studies on oocyte maturation have contributed
substantially in the discovery of some of the most important biochemical and cellular events like
functional significance of novel membrane-associated steroid receptors, elucidation of maturation promoting
factor (MPF), cytostatic factor (CSF) and other signalling cascades that entrain the cell cycle clock
to hormonal stimuli. While follicular estrogen has largely been implicated in maintenance of prophase
arrest, involvement of maturational steroid and membrane progestin receptor in resumption of meiotic
G2–M1 transition in piscine oocytes has been shown earlier. Moreover, detection of ovarian IGF system,
maturational gonadotropin stimulation of IGF ligands and potential synergism between maturational
steroid and IGF1 in zebrafish oocytes are most recent advancements. Though endocrine/paracrine regulation
of cyclic nucleotide-mediated signalling events in meiotic cell cycle progression is well established,
involvement of PI3K/Akt signalling cascade has also been reported in fish, amphibian and mammalian
oocytes. The major objective of this overview is to describe how fish oocytes maintain high cAMP/PKA
activity and how steroid- and/or growth factor-mediated signalling cascade regulate this pathway for
the withdrawal of meiotic arrest. Moreover, special emphasis is placed on some recent findings on interaction
of PKA with some of the MPF-regulating components (e.g., synthesis of cyclin B or MEK/MAPK signalling
cascade) for the maintenance of prophase arrest.
