Oocyte-secreted factor activation of SMAD 2/3 signaling enables initiation of mouse cumulus cell expansion.
Expansion of the mouse cumulus-oocyte complex (COC) is dependent on oocyte-secreted paracrine factors. Transforming growth factor beta (TGFB) superfamily molecules are prime candidates for the cumulus expansion-enabling factors (CEEFs), and we have recently determined that growth differentiation factor 9 (GDF9) alone is not the CEEF. The aim of this study was to examine oocyte paracrine factors and their signaling pathways that regulate mouse cumulus expansion. Using RT-PCR, oocytes were found to express the two activin subunits, Inhba and Inhbb, and activin A and activin B both enabled FSH-induced cumulus expansion of oocytectomized (OOX) complexes. Follistatin, an activin-binding protein, neutralized activin-induced expansion but had no effect on oocyte-induced expansion. The type I receptors for GDF9 and activin are activin receptor-like kinase 5 (ALK5) and ALK4, respectively, both of which activate the same SMAD 2/3 signaling pathway. We examined the requirement for this signaling system using an ALK 4/5/7 inhibitor, SB-431542. SB-431542 completely ablated FSH-stimulated GDF9-, activin A-, activin B-, and oocyte-induced cumulus expansion. Moreover, SB-431542 also antagonized epidermal growth factor-stimulated, oocyte-induced cumulus expansion. Using real-time RT-PCR, SB-431542 also attenuated GDF9-, activin A-, and oocyte-induced OOX expression of hyaluronan synthase 2, tumor necrosis factor alpha-induced protein 6, prostaglandin synthase 2, and pentraxin 3. This study provides evidence that the CEEF is composed of TGFB superfamily molecules that signal through SMAD 2/3 to enable the initiation of mouse cumulus expansion.
Dragovic
Rebecca A
RA
Research Centre for Reproductive Health, Discipline of Obstetrics and Gynaecology, Medical School, University of Adelaide, Adelaide, South Australia 5005, Australia.
Ritter
Lesley J
LJ
Schulz
Samantha J
SJ
Amato
Fred
F
Thompson
Jeremy G
JG
Armstrong
David T
DT
Gilchrist
Robert B
RB
D029404:Activin Receptors / Q000037:antagonists & inhibitors; D028341:Activins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D015153:Blotting, Western; D049109:Cell Proliferation; D004149:Dioxoles / Q000494:pharmacology; D005260:Female; D006107:Granulosa Cells / Q000378:metabolism; D051379:Mice; D009865:Oocytes / Q000502:physiology*; D019899:Paracrine Communication / Q000502:physiology; D010766:Phosphorylation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*; D051899:Smad2 Protein / Q000502:physiology*; D051900:Smad3 Protein / Q000502:physiology*; D014158:Transcription, Genetic / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000502:physiology
C459179:4-(5-benzo(1,3)dioxol-5-yl-4-pyridin-2-yl-1H-imidazol-2-yl)benzamide; D001549:Benzamides; D004149:Dioxoles; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D016212:Transforming Growth Factor beta; C422405:activin A; C044147:activin B; D028341:Activins; D029404:Activin Receptors