title: A Pbx1-dependent genetic and transcriptional network regulates spleen ontogeny.
abstract: The genetic control of cell fate specification, morphogenesis and expansion of the spleen, a crucial lymphoid organ, is poorly understood. Recent studies of mutant mice implicate various transcription factors in spleen development, but the hierarchical relationships between these factors have not been explored. In this report, we establish a genetic network that regulates spleen ontogeny, by analyzing asplenic mice mutant for the transcription factors Pbx1, Hox11 (Tlx1), Nkx3.2 (Bapx1) and Pod1 (capsulin, Tcf21). We show that Hox11 and Nkx2.5, among the earliest known markers for splenic progenitor cells, are absent in the splenic anlage of Pbx1 homozygous mutant (-/-) embryos, implicating the TALE homeoprotein Pbx1 in splenic cell specification. Pbx1 and Hox11 genetically interact in spleen formation and loss of either is associated with a similar reduction of progenitor cell proliferation and failed expansion of the splenic anlage. Chromatin immunoprecipitation assays show that Pbx1 binds to the Hox11 promoter in spleen mesenchymal cells, which co-express Pbx1 and Hox11. Furthermore, Hox11 binds its own promoter in vivo and acts synergistically with TALE proteins to activate transcription, supporting its role in an auto-regulatory circuit. These studies establish a Pbx1-Hox11-dependent genetic and transcriptional pathway in spleen ontogeny. Additionally, we demonstrate that while Nkx3.2 and Pod1 control spleen development via separate pathways, Pbx1 genetically regulates key players in both pathways, and thus emerges as a central hierarchical co-regulator in spleen genesis.
authors.affiliation: Department of Cell and Developmental Biology, Cornell University, Weill Medical School, New York, NY, 10021, USA.
authors.forename: Andrea
authors.initials: A
authors.lastname: Brendolan
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Ferretti
authors.forename: Valentina
authors.initials: V
authors.lastname: Salsi
authors.forename: Kelvin
authors.initials: K
authors.lastname: Moses
authors.forename: Susan
authors.initials: S
authors.lastname: Quaggin
authors.forename: Francesco
authors.initials: F
authors.lastname: Blasi
authors.forename: Michael L
authors.initials: ML
authors.lastname: Cleary
authors.forename: Licia
authors.initials: L
authors.lastname: Selleri
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D011401:Promoter Regions, Genetic; D013154:Spleen / Q000002:abnormalities / Q000196:embryology*; D014157:Transcription Factors / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology; D025721:WT1 Proteins / Q000096:biosynthesis / Q000235:genetics
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D018398:Homeodomain Proteins; D000075062:Pre-B-Cell Leukemia Transcription Factor 1; D014157:Transcription Factors; D025721:WT1 Proteins; C481797:Pbx1 protein, mouse; C112923:Tcf21 protein, mouse; C487378:Tlx1 protein, mouse; C107836:Tlx2 protein, mouse