Female mice null for the oocyte-specific gene product, growth differentiation factor-9 (GDF-9), a member of the transforming growth factor-beta superfamily, exhibit primary infertility due to failed ovarian follicular development. The purpose of this study is to characterize oocyte and follicular differentiation as a function of animal age using cell culture and fluorescence, confocal, and electron microscopy. Analysis of follicles from GDF-9 homozygous mutant mice indicates that GDF-9-deficient oocytes grow more rapidly than control oocytes and that follicle growth ceases at the type 3b stage. Based on germinal vesicle (GV) chromatin patterns, fully grown oocytes isolated from GDF-9-deficient mice progress to advanced stages of differentiation equivalent to those found in antral follicles of control (heterozygous) mice. In vitro maturation of oocytes from homozygous mutant mice revealed that most oocytes are capable of resuming meiosis, with the ability to achieve meiotic completion reaching the highest levels in 6-week-old mice. Among the characteristic ultrastructural features of oocytes from homozygous mutant mice are perinuclear organelle aggregation, unusual peripheral Golgi complexes, and a failure to form cortical granules. Modified interconnections between granulosa cells and oocytes were also observed by ultrastructural (EM) and fluorescence microscopic analysis of follicles from GDF-9-deficient mice. These modifications included a decrease in the number of actin-based transzonal processes and modifications of microtubule-based projections that over time gave rise to invasion of the perivitelline space with eventual loss of oocyte viability. These cell-cell aberrations suggest a critical role for GDF-9 in the regulation of growth in preantral follicles through a mechanism involving bidirectional somatic cell-germ cell interactions.
Copyright 1998 Academic Press.