Interplay between paracrine signaling and gap junctional communication in ovarian follicles.
Intercellular communication is required for ovarian folliculogenesis. This is apparent in mice lacking connexin43 (Cx43, a gap junction protein strongly expressed in granulosa cells), or growth/differentiation factor-9 (GDF9, an oocyte-specific growth factor that stimulates granulosa cell proliferation and differentiation), or in mice expressing a mutant form of Kit ligand (KITL, a paracrine factor that, in the ovary, is secreted by granulosa cells to stimulate oocyte growth). In all of these mutant lines, follicle growth is impaired suggesting a possible interaction between paracrine signaling and gap junctional communication. To assess this possibility, we analyzed gene expression in mutant ovaries. Despite the lack of gap junctional coupling between granulosa cells of Cx43 null mutant ovaries, expression of the genes encoding KITL and its receptor, KIT, is maintained. Furthermore, GDF9 expression is maintained. In GDF9 null mutant ovaries, there is no apparent change in Cx43 expression and, correspondingly, the granulosa cells remain coupled. There is also no increase in granulosa cell apoptosis in ovaries lacking Cx43 or GDF9. Staining for proliferating cell nuclear antigen (PCNA) revealed that the granulosa cells of Cx43 null mutant ovaries have a reduced frequency of DNA synthesis. Using both radiolabeled thymidine incorporation and PCNA staining in vitro, we showed that recombinant GDF9 could restore the proliferation of coupling-deficient granulosa cells to the level of control cells. These results indicate that impaired folliculogenesis in mice lacking Cx43 is due at least in part to reduced responsiveness of granulosa cells to oocyte-derived GDF9, indicating an interaction between these two modes of intercellular communication.
Gittens
Joanne E I
JE
Department of Physiology and Pharmacology, The University of Western Ontario, London, Ontario N6A 5C1, Canada.
Barr
Kevin J
KJ
Vanderhyden
Barbara C
BC
Kidder
Gerald M
GM
D000818:Animals; D017209:Apoptosis; D055430:Bone Morphogenetic Protein 15; D002450:Cell Communication; D049109:Cell Proliferation; D018031:Connexin 43 / Q000378:metabolism; D005260:Female; D017629:Gap Junctions / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006107:Granulosa Cells; D055429:Growth Differentiation Factor 9; D036341:Intercellular Signaling Peptides and Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008817:Mice, Mutant Strains; D016513:Mice, SCID; D006080:Ovarian Follicle / Q000166:cytology / Q000502:physiology*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D019089:Stem Cell Factor / Q000378:metabolism
C525902:Bmp15 protein, mouse; D055430:Bone Morphogenetic Protein 15; D018031:Connexin 43; C525898:Gdf9 protein, mouse; D055429:Growth Differentiation Factor 9; D036341:Intercellular Signaling Peptides and Proteins; D018809:Proliferating Cell Nuclear Antigen; D011994:Recombinant Proteins; D019089:Stem Cell Factor