title: Temporally regulated overexpression of parathyroid hormone-related protein in the mammary gland reveals distinct fetal and pubertal phenotypes.
abstract: We have previously demonstrated that overexpression of parathyroid hormone-related protein (PTHrP) in the mammary glands of transgenic mice results in defects in ductal elongation and branching during puberty and in lobuloalveolar development during pregnancy. In addition, we have shown that PTHrP is necessary for the formation of the initial ductal tree during embryonic mammary development. In order to examine the effect of varying the timing of PTHrP overexpression on mammary development, we created tetracycline-regulated, K14-tTA/Tet(O)-PTHrP double transgenic mice. In this report, we document that this 'tet-off' system directs transgene expression to the mammary gland and that it is fully repressed in the presence of tetracycline. Using these mice, we demonstrate that transient overexpression of PTHrP before birth causes defects in ductal branching during puberty and that overexpression of PTHrP during puberty decreases the rate of ductal elongation. Furthermore, we demonstrate that if PTHrP overexpression is initiated after ductal morphogenesis is completed, lobuloalveolar development is unaffected. Finally, we demonstrate that the impairment in ductal elongation caused by PTHrP is associated with an increase in the basal rate of epithelial cell apoptosis in terminal end buds and a failure to increase end bud cell proliferation and decrease apoptosis in response to estrogen and progesterone.
authors.affiliation: Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Dunbar
authors.forename: P
authors.initials: P
authors.lastname: Dann
authors.forename: C W
authors.initials: CW
authors.lastname: Brown
authors.forename: J
authors.initials: J
authors.lastname: Van Houton
authors.forename: B
authors.initials: B
authors.lastname: Dreyer
authors.forename: W P
authors.initials: WP
authors.lastname: Philbrick
authors.forename: J J
authors.initials: JJ
authors.lastname: Wysolmerski
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D005314:Embryonic and Fetal Development / Q000502:physiology; D005260:Female; D018507:Gene Expression Regulation, Developmental; D008321:Mammary Glands, Animal / Q000166:cytology / Q000196:embryology / Q000254:growth & development*; D051379:Mice; D008822:Mice, Transgenic; D009024:Morphogenesis / Q000502:physiology; D044162:Parathyroid Hormone-Related Protein; D010641:Phenotype; D011506:Proteins / Q000235:genetics / Q000502:physiology*; D013752:Tetracycline
chemical_list: D044162:Parathyroid Hormone-Related Protein; D011506:Proteins; D013752:Tetracycline