PROJECT SUMMARY / ABSTRACT
Infertility afflicts about 10% of women between the ages of 15 and 44 and can be triggered by a wide range of
conditions, including disease, therapeutic treatment for disease, toxins, and age. Although these conditions
often impair fertility by affecting oocyte quality, our limited understanding of how the oocyte communicates with
its environment has hampered the development of effective therapeutic strategies. Oocyte development
depends absolutely on contact with somatic granulosa cells in the ovarian follicle. When communication with
the granulosa cells is impaired, functional oocytes are not produced. This intercellular communication is
mediated through long cytoplasmic filaments, termed transzonal projections (TZPs), that extend from the
granulosa cells and penetrate the thick extracellular coat (zona pellucida) that surrounds the germ cell to reach
the oocyte plasma membrane. Although TZPs are the sole means by which the granulosa cells and growing
oocytes physically communicate, no research has addressed when or how these unique structures form. Our
preliminary data indicates that the number of TZPs increases substantially during the growth phase of
oogenesis. Strikingly, the granulosa cells adjacent to growing oocytes express highly conserved activators of
filopodial growth, and the oocyte-derived TGFß superfamily member, GDF (growth-differentiation factor)-9
increases the number of TZPs projecting from the surrounding granulosa cells. We propose that TZPs are
specialized filopodia that are dynamically elaborated from the granulosa cells surrounding growing oocytes and
that TZP formation is regulated by TGFß superfamily members secreted by the oocyte whose effect is
transduced through SMAD4-dependent signaling in the granulosa cells. Using a combination of genetic and in
vitro approaches, we will determine whether GDF-SMAD4 signaling regulates (i) expression and/or localization
of filopodial assembly factors, (ii) TZP formation and (iii) gap junctional coupling between the oocyte and the
granulosa cells. This new model of TZP formation differs fundamentally from current understanding because it
emphasizes that the physical lines of communication that link the oocyte to its somatic environment are
dynamic structures, and therefore are subject to genetic and epigenetic influences. It will establish a new
paradigm for understanding how – by influencing TZP formation, function or stability – disease and
environmental conditions can compromise oocyte quality. It will also provide a novel conceptual platform for
designing and developing new strategies to rescue fertility in women and will help propel new efforts to derive
functional oocytes from pluripotent stem cells.
