STIMULATION OF XENOPUS OOCYTE MATURATION BY INHIBITION OF THE G-PROTEIN ALPHA-S SUBUNIT, A COMPONENT OF THE PLASMA-MEMBRANE AND YOLK PLATELET MEMBRANES
Cj. Gallo et al., STIMULATION OF XENOPUS OOCYTE MATURATION BY INHIBITION OF THE G-PROTEIN ALPHA-S SUBUNIT, A COMPONENT OF THE PLASMA-MEMBRANE AND YOLK PLATELET MEMBRANES, The Journal of cell biology, 130(2), 1995, pp. 275-284
Oocytes of Xenopus laevis undergo maturation when injected with an aff
inity-purified antibody against the COOH-terminal decapeptide of the a
lpha subunit of the G-protein G(s), an antibody that inhibits G(s) act
ivity. Germinal vesicle breakdown, chromosome condensation, and polar
body formation occur, with a time course similar to that for oocytes t
reated with progesterone. The alpha(s) antibody-injected oocytes also
acquire the ability to be activated by sperm. Coinjection of the catal
ytic subunit of cAMP-dependent protein kinase, or incubation with cycl
oheximide, inhibits maturation in response to injection of the alpha(s
) antibody; these experiments show that the alpha(s) antibody acts at
an early point in the pathway leading to oocyte maturation, before for
mation of maturation promoting factor, and like progesterone, its acti
on requires protein synthesis. Immunogold electron microscopy shows th
at alpha(s) is present in the yolk platelet membranes as well as the p
lasma membrane. These results support the hypothesis that progesterone
acts by inhibiting alpha(s) and suggest that the target of progestero
ne could include yolk platelet membranes as well as the plasma membran
e.