title: barx1 is necessary for ectomesenchyme proliferation and osteochondroprogenitor condensation in the zebrafish pharyngeal arches.
abstract: Barx1 modulates cellular adhesion molecule expression and participates in specification of tooth-types, but little is understood of its role in patterning the pharyngeal arches. We examined barx1 expression during zebrafish craniofacial development and performed a functional analysis using antisense morpholino oligonucleotides. Barx1 is expressed in the rhombencephalic neural crest, the pharyngeal arches, the pectoral fin buds and the gut in contrast to its paralogue barx2, which is most prominently expressed in the arch epithelium. Additionally, barx1 transient expression was observed in the posterior lateral line ganglia and developing trunk/tail. We show that Barx1 is necessary for proliferation of the arch osteochondrogenic progenitors, and that morphants exhibit diminished and dysmorphic arch cartilage elements due to reductions in chondrocyte differentiation and condensation. Attenuation of Barx1 results in lost arch expression of osteochondrogenic markers col2a1, runx2a and chondromodulin, as well as odontogenic marker dlx2b. Further, loss of barx1 positively influenced gdf5 and chordin, markers of jaw joint patterning. FGF signaling is required for maintaining barx1 expression, and that ectopic BMP4 induces expression of barx1 in the intermediate region of the second pharyngeal arch. Together, these results indicate an essential role for barx1 at early stages of chondrogenesis within the developing zebrafish viscerocranium.
authors.affiliation: Laboratory of Molecular Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, 9000 Rockville Pike, Bethesda, MD 20892, USA. sperbers@mail.nih.gov
authors.forename: Steven M
authors.initials: SM
authors.lastname: Sperber
authors.forename: Igor B
authors.initials: IB
authors.lastname: Dawid
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000378:metabolism; D001934:Branchial Region / Q000196:embryology*; D049109:Cell Proliferation; D020219:Chondrogenesis; D004625:Embryo, Nonmammalian / Q000378:metabolism; D005346:Fibroblast Growth Factors / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics; D006801:Humans; D051379:Mice; D009432:Neural Crest / Q000196:embryology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015027:Zebrafish / Q000196:embryology*; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C490667:BARX1 protein, human; C525809:BMP4 protein, human; C095587:Barx1 protein, mouse; C531180:Barx1 protein, zebrafish; C525810:Bmp4 protein, mouse; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D018398:Homeodomain Proteins; D014157:Transcription Factors; D029961:Zebrafish Proteins; C525813:bmp4 protein, zebrafish; D005346:Fibroblast Growth Factors