- Packer AI, Hsu YC, Besmer
P, Bachvarova RF
- Dev Biol 1994 Jan 161:1
194-205
- Abstract
- Both genetic and descriptive
studies have implicated the c-kit receptor and its ligand, KL,
in the process of oocyte growth in the postnatal mouse ovary.
In order to test the hypothesis that KL is an oocyte growth factor,
we used an oocyte culture system to study its effects in vitro.
Initial experiments established that both ovarian c-kit and KL
are biologically active. An immune complex kinase assay demonstrated
that ovarian c-kit, found primarily on oocytes, has autophosphorylation
activity, and a bone marrow-derived mast cell coculture assay
indicated that granulosa cells produce functional KL. The addition
of 10 ng/ml KL to growing follicles cultured in collagen gels
resulted in a 67% increase in the rate of oocyte growth, and a
doubling of the rate was achieved at around 50 ng/ml. ACK2, a
monoclonal antibody against c-kit, severely inhibited the growth
of late fetal and neonatal oocytes in coculture with ovarian cells
and had less effect on growing oocytes cultured in follicles from
10- to 11-day-old mice. Genistein, an inhibitor of tyrosine kinases,
including c-kit, blocked oocyte growth and disrupted follicle
morphology. In initial studies on the regulation of KL production
in granulosa cells, we found that both dibutyryl cyclic AMP and
growing oocytes were able to induce increased KL mRNA accumulation
in granulosa cell monolayers as assessed by Northern analysis.
These studies demonstrate that c-kit and KL are required for maintenance
of oocyte growth in vitro.
Excerpts
Ín
the presence of genistein, many of the follicles became disorganized
and the oocytes became partially denuded (Fig. 6B). There
also appeared to be less granulosa cell proliferation compared to
the control follicles. This result suggests that tyrosine
phophorylation is important for granulosa cell proliferation and
follicle organization, as well as for oocyte growth.
Evidence
is accumulating that the oocyte is important for normal granulosa
cell proliferation and differentiation.
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