PRK2在海星卵成熟期間之訊息傳遞

Animal oocytes grow and acquire all the
required mRNA and proteins for the early
embryonic development. After growth
oocytes arrest in the prophase of meiosis I
until the stimulation of maturation hormone.
In starfish, maturation hormone,
1-methyladenine (1-MA), triggers the
activation of maturation promoting factor,
which is a major driving force for the
resumption of meiosis. At the mean time,
the protein synthesis machinery is also
activated for translating stored mRNA. 1-MA
is known to induce the activation of
inhibitory G protein that leads to a bifurcate
pathway including the activation of PI3
kinase and inactivation of adenylyl cyclase.
Although, we know both the increase in PI3
kinase and the decrease in adenylyl cyclase
activities are required for activation of MPF
and protein synthesis, the downstream
effectors of these signaling pathways are
unclear. Shortly after the induction of
1-MA, there is an increase in protein kinase
C like activity, which precedes the activation
of MPF and initiation of protein synthesis.
Later, this PKC-like activity is proved to be
mainly due to the protein kinase C-related
kinase 2 (PRK2). The initiation of protein
synthesis is activated by phosphorylation of
eukaryotic initiation factor 4E (eIF4E).
Recently, I further demonstrated that PRK2
phosphoryaltes eIF4E in vitro. (Lee et al.,
2000. Dev Biol. 228, 166-180.). In addition,
PRK2 activity is regulated by 1-MA-induced
PI3 kinase and adenylyl cyclase-dependent
pathway. These observations suggest PRK2
is the key molecule mediating this
G-protein-induced event during meiotic
maturation in starfish. However, the
definite proof awaits PRK2 functional study in vivo. This study aims to elucidate the
role and regulation of PRK2 during meiotic
maturation in starfish oocytes. Specifically,
I will ask whether the role of PRK2 in vivo
can be determined using known PRK2
activators and inhibitors, including a
constitutively active and a dominant-negative
PRK2. Due to the lack of the same starfish
species used in previous studies, our
laboratory is trying to use a native starfish,
Archaster typicus, collected at the beach of
PenHu. We have established a system for
testing the responses of Archaster typicus
oocytes to maturation hormone. In addition,
we also generated (1) a constitutively active
PRK2 by removing the regulatory domain
and (2) a dominant-negative mutant by
changing PRK2 amino acid 666 from a lysine
to an arginine. The effects of PRK2
mutants described on the maturation
responses of Archaster typicus oocytes are
underway.