CCAAT/Enhancer Binding Proteins (C/EBP)- and - are Essential for Ovulation, Luteinization and the Expression of Key Target Genes

Luteinizing hormone (LH) activation of the EGF receptor/RAS/ERK1/2 pathway is essential for ovulation and luteinization because granulosa cell depletion of Erk1/2 (Erk1/2gc-/- mice) renders mice completely infertile. Because of their potential as mediators of ERK1/2-dependent granulosa cell differentiation, we disrupted genes encoding the CCAAT/enhancer-binding proteins, (C/EBP) a and C/EBPb. Female Cebpbgc-/- mutant mice but not Cebpagc-/- mice were subfertile whereas Cebpa/bgc-/- double mutant females were sterile. Follicles failed to ovulate, ovaries were devoid of corpora lutea, luteal cell marker genes (Lhcgr, Prlr, Ptgfr, Cyp11a1 and Star) were absent and serum progesterone levels were low. Microarray analyses identified numerous C/EBPa/b target genes in eCG-hCG treated mice. At 4h post-hCG, a subset (19%) of genes altered in the Cebpa/b depleted cells was also altered in Erk1/2 depleted cells; hence they are common effectors of ERK1/2. Additional genes down-regulated in the Cebpa/b depleted cells at 8 and 24h post-hCG include known (Akr1b7, Runx2, Star, Saa3) and novel (Abcb1b, Apln, Igfbp4, Prlr, Ptgfr Timp4) C/EBP target genes including effectors of vascular cell development. Bhmt, a gene controlling methionine metabolism and expressed exclusively in liver and kidney, was high in WT luteal cells but totally absent in Cebpa/b mutant cells. Because numerous genes potentially associated with vascular development were suppressed in the mutant cells, C/EBPa/b appear to dictate the luteinization process by also controlling genes that regulate the formation of the extensive vascular network required to sustain luteal cells. Thus, C/EBPa/b mediate several aspects of granulosa cell differentiation as well as the complex process of luteinization.

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