title: Identification of a basic helix-loop-helix transcription factor expressed in mammary gland alveolar cells and required for maintenance of the differentiated state.
abstract: The development of mammary glands relies on complicated signaling pathways that control cell proliferation, differentiation, and apoptotic events through transcriptional regulatory circuits. A key family of transcription factors used in mammary gland development is the helix-loop-helix/basic helix-loop-helix (HLH/bHLH) protein family. In this study, we identify Mist1 as a tissue-restricted Class II bHLH transcription factor expressed in lactating mammary glands. Mouse and human mammary glands accumulated Mist1 protein exclusively in secretory alveolar cells, and Mist1 transcripts were differentially expressed in mouse SCp2 cells induced to differentiate by addition of lactogenic hormones. Mist1 null (Mist1(KO)) lactating mammary glands were defective in normal lobuloalveolar organization, exhibiting shedding of cells into the alveolus lumen and premature activation of the signal transducer and activator of transcription 3 signaling pathway. These cells also failed to maintain expression of the gap junction proteins connexin26 and connexin32, leading to the loss of gap junctions. Our findings suggest that loss of Mist1 impairs the maintenance of the fully differentiated alveolar state and, for the first time, places Mist1 within the hierarchy of known HLH/bHLH proteins that control mammary epithelial cell development.
authors.affiliation: Department of Biological Sciences and the Purdue Cancer Center, Purdue University, West Lafayette, Indiana 47907-2064, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Carina
authors.initials: C
authors.lastname: Johansson
authors.forename: Thai
authors.initials: T
authors.lastname: Tran
authors.forename: Ryan
authors.initials: R
authors.lastname: Bettencourt
authors.forename: Yoko
authors.initials: Y
authors.lastname: Itahana
authors.forename: Pierre-Yves
authors.initials: PY
authors.lastname: Desprez
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Konieczny
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D000072259:Connexin 26; D017630:Connexins; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D008321:Mammary Glands, Animal / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D050796:STAT3 Transcription Factor / Q000378:metabolism
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D000072259:Connexin 26; D017630:Connexins; D050796:STAT3 Transcription Factor; C491312:Bhlha15 protein, mouse; C000607042:GJB2 protein, human; C494087:Stat3 protein, mouse