Human Reproduction, Vol 12, 2226-2234, Copyright © 1997 by Oxford University Press
M Antczak, J Van Blerkom and A Clark
This study describes the occurrence of a highly specialized subpopulation
of granulosa and cumulus oophorus cells that accumulate and sequester
specific growth factors by a novel mechanism. These cells are characterized
by multiple balloon-like processes tethered to the cell by means of a
slender stalk of plasma membrane. Time-lapse analyses demonstrate that
these tethered structures (TS) form in minutes and frequently detach from
the cell with the bulbous portion remaining motile on the cell surface.
Serial section reconstruction of transmission electron microscopic images
shows a specific and stable intracellular organization in which an apparent
secretory compartment composed of densely packed vacuoles, vesicles, and
cisternae is separated by a thick filamentous network from a nuclear
compartment containing mitochondria, polyribosomes, lipid inclusions, and
rough- surfaced endoplasmic reticulum. Immunofluorescent analysis performed
during the formation of these structures showed a progressive accumulation
of vascular endothelial growth factor, leptin, and transforming growth
factor-beta2 in the bulbous region. TS were identified in newly aspirated
masses of granulosa and cumulus oophorus, and their production persists for
months in culture. Observations of TS- forming cells made over several days
of culture indicates that their production is episodic and factor release
from these cells may be pulsatile. The findings suggest that a novel method
of growth factor storage and release by an apparent apocrine-like mechanism
occurs in the human ovarian follicle. The results are discussed with
respect to possible roles in pre- and post-ovulatory follicular
development.
ARTICLES
A novel mechanism of vascular endothelial growth factor, leptin and transforming growth factor-beta2 sequestration in a subpopulation of human ovarian follicle cells
Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder 80309, USA.
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