Granulosa Cell Ligand NPPC and Its Receptor NPR2 Maintain Meiotic Arrest in Mouse Oocytes

Abstract

Granulosa cells of mammalian Graafian follicles maintain oocytes in meiotic arrest, which prevents the precocious maturation. We show that mouse mural granulosa cells, which line the follicle wall, express natriuretic peptide precursor type C, Nppc, mRNA while cumulus cells surrounding oocytes express mRNA of the NPPC receptor NPR2, a guanylyl cyclase. NPPC elevated cGMP levels in cumulus cells and oocytes and inhibited meiotic resumption in vitro. Meiotic arrest was not sustained in most Graafian follicles of Nppc or Npr2 mutant mice, and meiosis resumed precociously. Oocyte-derived paracrine factors promoted cumulus cell expression of Npr2 mRNA. Therefore, the granulosa cell ligand NPPC and its receptor NPR2 in cumulus cells prevent precocious meiotic maturation, which is critical for maturation and ovulation synchrony and for normal female fertility.Meiosis is a germ cell-specific process that reduces the number of chromosomes from the diploid to the haploid number. It begins in human and mouse ovaries during fetal life but meiotic progression becomes arrested for prolonged periods at the diplotene stage of meiotic prophase. Fully-grown mammalian oocytes in Graafian follicles are maintained in meiotic prophase arrest until the preovulatory surge of luteinizing hormone (LH) triggers the resumption of meiosis and ovulation. The mature oocytes (eggs) are then available for fertilization within the oviduct. The somatic cell compartment of Graafian follicles, consisting of mural granulosa cells lining the inside of the follicle wall and cumulus cells surrounding the oocyte, plays a crucial role in maintaining oocyte meiotic arrest in mammals since removal of the oocyte-cumulus cell complex from these follicles results in gonadotropin-independent meiotic resumption in culture (1,2). Cyclic nucleotides cAMP and cGMP are crucial to the maintenance of meiotic arrest. Cyclic AMP is generated within oocytes downstream of GPR3 and GPR12, regulators of Gs proteins controlling adenylyl cyclase (3,4). Inability to sustain oocyte cAMP levels leads to precocious gonadotropinindependent resumption of meiosis, which interrupts the synchrony between oocyte maturation and ovulation and compromises female fertility (3-5). PDE3A, an oocytespecific phosphodiesterase, becomes activated after the LH-surge to decrease cAMP levels in oocytes and thereby initiates pathways governing meiotic resumption (6). Before the LHsurge, cGMP, originating in granulosa cells of the follicular somatic compartment and transferred to the oocyte via gap junctions, inhibits activity of PDE3A in the oocyte (7,8). Therefore, control of cGMP production by granulosa cells is crucial for maintaining meiotic arrest in fully-grown oocytes. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptExploration of the mouse cumulus cell transcriptome for mRNAs encoding guanylyl cyclases using microarray analysis (9) revealed abundant expression of natriuretic peptide receptor 2 (Npr2, also called GC-B) mRNA. The presence of this guanylyl cyc...

Compensatory functions of histone deacetylase 1 (HDAC1) and HDAC2 regulate transcription and apoptosis during mouse oocyte development

“…Ovaries from 12-and 18-d-old mice were fixed for 2 to 3 h at room temperature in Bouin solution, dehydrated in ethanol and toluene, and embedded in paraffin. Follicles were categorized and counted by examining serial 5-μm sections through the entire ovary and stained with periodic acid/Schiff reagent and Lillie-Mayer hematoxylin (57,61).…”

Oocyte–cumulus cell interactions regulate free intracellular zinc in mouse oocytes

“…Oocytes enable MAKP3/1 signaling in cumulus cells by promoting expression of the epidermal growth factor (EGF) receptor . Cumulus cells, in turn, supply the oocyte with nutrients , Sugiura et al 2007, Su et al 2008, induce transcriptional silencing (De La Fuente & Eppig 2001) and prevent resumption of meiosis before ovulation (Pincus & Enzmann 1935, Zhang et al 2010). …”

Growth and differentiation factor 9 promotes oocyte growth at the primary but not the early secondary stage in three-dimensional follicle culture

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