Epimorphin acts extracellularly to promote cell sorting and aggregation during the condensation of vertebral cartilage.
Formation of vertebrae occurs via endochondral ossification, a process involving condensation of precartilaginous cells. Here, we provide the first molecular evidence of mechanism that underlies initiation of this process by showing that the extracellular factor, Epimorphin, plays a role during early steps in vertebral cartilage condensation. Epimorphin mRNA is predominantly localized in the vertebral primordium. When provided exogenously in ovo, it causes precocious differentiation of chondrocytes, resulting in the formation of supernumerary vertebral cartilage in chicken embryos. To further analyze its mode of action, we used an in vitro co-culture system in which labeled 10T1/2 or sclerotomal prechondrogenic cells were co-cultured with unlabeled Epimorphin-producing cells. In the presence of Epimorphin, the labeled cells formed tightly packed aggregates, and sclerotomal cells displayed augmented accumulation of NCAM and other early markers of chondrocyte differentiation. Finally, we found that the Epimorphin expression is initiated during vertebrogenesis by Sonic hedgehog from the notochord mediated by Sox 9. We present a model in which successive action of Epimorphin in recruiting and stacking sclerotomal cells leads to a sequential elongation of a vertebral primordium.
Oka
Yumiko
Y
Research Planning Department, Sumitomo Electric Industries LTD., 1-13-12, Motoakasaka, Tokyo 107-8468, Japan.
Sato
Yuki
Y
Tsuda
Hokari
H
Hanaoka
Kazunori
K
Hirai
Yohei
Y
Takahashi
Yoshiko
Y
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002356:Cartilage / Q000196:embryology* / Q000378:metabolism; D002449:Cell Aggregation; D002454:Cell Differentiation; D002642:Chick Embryo; D002522:Chlorocebus aethiops; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D053823:Hedgehog Proteins; D006609:High Mobility Group Proteins / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D009024:Morphogenesis; D019006:Neural Cell Adhesion Molecules / Q000378:metabolism; D009672:Notochord / Q000166:cytology* / Q000378:metabolism; D011784:Quail; D012333:RNA, Messenger / Q000096:biosynthesis; D055758:SOX9 Transcription Factor; D015534:Trans-Activators / Q000502:physiology; D014157:Transcription Factors / Q000378:metabolism
D053823:Hedgehog Proteins; D006609:High Mobility Group Proteins; D008565:Membrane Proteins; D019006:Neural Cell Adhesion Molecules; D012333:RNA, Messenger; C509239:SHH protein, human; D055758:SOX9 Transcription Factor; C527932:SOX9 protein, human; D015534:Trans-Activators; D014157:Transcription Factors