Collagen gene expression during limb cartilage differentiation.

Abstract

Abstract. As limb mesenchymal cells differentiate into chondrocytes, they initiate the synthesis of type II collagen and cease synthesizing type I collagen. Changes in the cytoplasmic levels of type I and type II collagen mRNAs during the course of limb chondrogenesis in vivo and in vitro were examined using cloned cDNA probes. A striking increase in cytoplasmic type II collagen m R N A occurs coincident with the crucial condensation stage of chondrogenesis in vitro, in which prechondrogenic mesenchymal cells become closely juxtaposed before depositing a cartilage matrix. Thereafter, a continuous and progressive increase in the accumulation of cytoplasmic type II coUagen m R N A occurs which parallels the progressive accumulation of cartilage matrix by ceils. The onset of overt chondrogenesis, however, does not involve activation of the transcription of the type II collagen gene. Low levels of type II collagen m R N A are present in the cytoplasm of prechondrogenic mesenchymal cells at the earliest stages of limb development, well before the accumulation of detectable levels of type II collagen. Type I collagen gene expression during chondrogenesis is regulated, at least in part, at the translational level. Type I collagen mRNAs are present in the cytoplasm of differentiated chondrocytes, which have ceased synthesizing detectable amounts of type I collagen. T HE onset of cartilage differentiation in the developinglimb is characterized by a transient cellular condensation or aggregation process in which prechondrogenic mesenchymal cells become closely juxtaposed to one another before initiating cartilage matrix deposition. During this process, a cell-cell interaction, cell shape change, or some other event occurs which is necessary to trigger the chondrogenic differentiation of the cells (15). The critical condensation process may be initiated, at least in part, by a progressive decrease in the accumulation of extracellular hyaluronate (20,35). Fibronectin and type I collagen have been implicated in the cell-cell interaction occurring during condensation (7, 21, 34). Prostaglandin-mediated elevations in cAMP levels during condensation are involved in regulating chondrogenesis (3, 6, 11, 14, 16-18, 32, 33). A change in the shape of the cells from a flattened mesenchymal morphology to a rounded configuration also plays an important role in the process (2, 41).Although considerable insight has been gained into the extracellular influences and intracellular regulatory molecules that are involved in regulating limb chondrogenesis, virtually nothing is known about the molecular mechanisms by which these factors directly influence the changes in gene activity that occur during cartilage differentiation. Prechondrogenic limb mesenchymal cells synthesize type I collagen (36). As the cells differentiate into chondrocytes, they initiate the synthesis of cartilage-characteristic type II collagen and cease synthesizing type I collagen (36). Thus the conversion of mesenchymal chondrogenic progenitor cells into chondrocytes i...

Assessment of the gene expression profile of differentiated and dedifferentiated human fetal chondrocytes by microarray analysis

“…These results are in accord with a large body of previously reported results concerning the dedifferentiation of chondrocytes from multiple species. We also observed the up-regulation of numerous genes encoding ECM proteins associated with the fibroblastic or prechondrogenic phenotype displayed by dedifferentiated cells, including COL1A1 and tenascin (37)(38)(39)(40).…”

“…These changes in the biosynthetic profile of dedifferentiated chondrocytes resemble some of the phenotypic changes displayed by OA chondrocytes, and the matrix they produce is similar to that synthesized by chondroprogenitor cells (7)(8)(9)(10)(11)(12)(13)17,(37)(38)(39)(40). However, the mechanisms responsible for the phenotypic instability of chondrocytes and the regulation of these different chondrocyte-specific phenotypes remain poorly understood.…”

Development of a cellular model to study alternative splicing of type II collagen gene

“…A key step in chondrocyte differentiation is expression of the type I1 collagen (COL2) gene [3]. Alternative splicing of tlie COL2 pre-mRNA produces two mature niRNAs: COL2A, which retains exon 2, and COL2B, which lacks this exon [ 5 ] .…”

Fibroblast growth factor signaling in skeletal development and disease

“…Mesenchymal condensations form in the developing limb bud and are characterized by the aggregation of loose mesenchymal cells and the expression of extracellular matrix proteins, cell adhesion molecules, transcription factors, and receptors for signaling molecules. The transcription factor Sox9 is required for the differentiation of the chondrogenic lineage, and bone morphogenetic protein (BMP) receptors 1a and 1b are required for chondrogenesis and the maintenance of Sox9 expression (Kosher et al 1986;Nah et al 1988;Bi et al 1999;Akiyama et al 2002;Yoon et al 2005;Yeung Tsang et al 2014;Lim et al 2015). Proliferating cells within the forming mesenchymal condensation express type II collagen (Col2a1) centrally in chondroprogenitors and type I collagen (Col1a1) peripherally in osteoprogenitors (Kosher et al 1986).…”