title: Hand2 regulates chondrogenesis in vitro and in vivo.
abstract: Hand2 is a transcription factor of the basic helix-loop-helix family that plays essential roles during development. Hand2 determines the anterior-posterior axis during limb development and there is also substantial evidence that Hand2 regulates limb skeletogenesis. However, little is known about how Hand2 might regulate skeletogenesis. Here we show that, in a limb bud micromass culture system, over-expression of Hand2 represses chondrogenesis and the expression of chondrocytic genes, Sox9, type II collagen and aggrecan. Furthermore, we show that Hand2 is induced by the activation of canonical Wnt signaling, which strongly represses chondrogenesis. Surprisingly, Hand2 repressed chondrogenesis in a DNA binding- and dimer formation-independent manner. To examine the in vivo role of Hand2 in mice, we targeted the expression of Hand2 to the cartilage using regulatory elements from the collagen II gene. The resulting transgenic mice displayed a dwarf phenotype, with axial, appendicular and craniofacial skeletal deformities. Hand2 strongly inhibited chondrogenesis in the axial and cranial base skeleton. In the sternum, Hand2 inhibited endochondral ossification by slowing chondrocyte maturation. These data support a model of Hand2 regulating endochondral ossification via at least two steps: (1) determination of the site of chondrogenesis by outlining the region of the future cartilage template and (2) regulation of the rate of chondrocyte maturation.
authors.affiliation: Department of Oral Anatomy and Developmental Biology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka, Japan. m-abe@dent.osaka-u.ac.jp
authors.forename: Makoto
authors.initials: M
authors.lastname: Abe
authors.forename: Ikumi
authors.initials: I
authors.lastname: Michikami
authors.forename: Toshiya
authors.initials: T
authors.lastname: Fukushi
authors.forename: Akiko
authors.initials: A
authors.lastname: Abe
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Maeda
authors.forename: Takashi
authors.initials: T
authors.lastname: Ooshima
authors.forename: Satoshi
authors.initials: S
authors.lastname: Wakisaka
mesh_terms: D053674:Aggrecans / Q000235:genetics / Q000378:metabolism; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002460:Cell Line; D020219:Chondrogenesis / Q000235:genetics / Q000502:physiology*; D024043:Collagen Type II / Q000235:genetics / Q000378:metabolism; D005121:Extremities / Q000196:embryology; D005260:Female; D005838:Genotype; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D066298:In Vitro Techniques; D008297:Male; D008648:Mesoderm / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055758:SOX9 Transcription Factor / Q000235:genetics / Q000378:metabolism
chemical_list: D053674:Aggrecans; D051792:Basic Helix-Loop-Helix Proteins; D024043:Collagen Type II; D055758:SOX9 Transcription Factor; C498766:Hand2 protein, mouse