title: Nulliparous CCAAT/enhancer binding proteindelta (C/EBPdelta) knockout mice exhibit mammary gland ductal hyperlasia.
abstract: CCAAT/Enhancer binding proteins (C/EBPs) are a family of nuclear proteins that function in the control of cell growth, death, and differentiation. We previously reported that C/EBPdelta plays a key role in mammary epithelial cell G(0) growth arrest. In this report, we investigated the role of C/EBPdelta in mammary gland development and function using female mice homozygous for a targeted deletion of C/EBPdelta (C/EBPdelta -/-). C/EBPdelta -/- females develop normally and exhibit normal reproductive and lactational performance. Adult nulliparous C/EBPdelta -/- females, however, exhibit mammary epithelial cell growth control defects. The mean number of mammary ductal branches is significantly higher in adult nulliparous C/EBPdelta -/- females compared with C/EBPdelta +/+ (wild-type control) females (66.8 +/- 5.2 vs 42.9 +/- 6.3 branch points/field, P < 0.01). In addition, the mean total mammary gland cellular volume occupied by epithelium is significantly higher in adult nulliparous C/EBPdelta -/- females compared with C/EBPdelta +/+ controls (29.0 +/- 1.4 vs 20.4 +/- 1.3, P < 0.001). Our results showed that the BrdU labeling index was significantly higher in mammary epithelial cells from nulliparous C/EBPdelta -/- females compared with C/EBPdelta +/+ controls during the proestrus/estrus (4.55 +/- 0.70 vs 2.14 +/- 0.43, P < 0.01) and metestrus/diestrus (6.92 +/- 0.75 vs 3.98 +/- 0.43 P < 0.01) phases of the estrus cycle. In contrast, the percentage of mammary epithelial cells undergoing apoptosis during both phases of the estrus cycle did not differ between C/EBPdelta -/- and C/EBPdelta +/+ females. The increased epithelial cell content and proliferative capacity was restricted to the nulliparous C/EBPdelta -/- females as no differences in mammary gland morphology, ductal branching or total epithelial content were observed between multiparous C/EBPdelta -/- and C/EBPdelta +/+ females. These results demonstrate that C/EBPdelta plays a novel role in mammary epithelial cell growth control that appears to be restricted to the nulliparous mammary gland.
authors.affiliation: Department of Veterinary Biosciences and Division of Molecular Biology and Cancer Genetics, Ohio State Comprehensive Cancer Center, Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Gigliotti
authors.forename: Peter F
authors.initials: PF
authors.lastname: Johnson
authors.forename: Esta
authors.initials: E
authors.lastname: Sterneck
authors.forename: James W
authors.initials: JW
authors.lastname: DeWille
mesh_terms: D000818:Animals; D017209:Apoptosis; D015152:Blotting, Northern; D051743:CCAAT-Enhancer-Binding Protein-delta; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000502:physiology*; D002455:Cell Division; D004971:Estrus; D005260:Female; D005348:Fibrocystic Breast Disease / Q000235:genetics*; D015870:Gene Expression; D051379:Mice; D018345:Mice, Knockout; D014157:Transcription Factors
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; C497253:Cebpd protein, mouse; D014157:Transcription Factors; D051743:CCAAT-Enhancer-Binding Protein-delta