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Mol. Cell. Biol., Aug 1996, 4512-4523, Vol 16, No. 8
V Lefebvre, G Zhou, K Mukhopadhyay, CN Smith, Z Zhang, H Eberspaecher, X Zhou, S Sinha, SN Maity and B de Crombrugghe
The molecular mechanisms by which mesenchymal cells differentiate into
chondrocytes are still poorly understood. We have used the gene for a
chondrocyte marker, the proalpha1(II) collagen gene (Col2a1), as a model to
delineate a minimal sequence needed for chondrocyte expression and identify
chondrocyte-specific proteins binding to this sequence. We previously
localized a cartilage-specific enhancer to 156 bp of the mouse Col2a1
intron 1. We show here that four copies of a 48-bp subsegment strongly
increased promoter activity in transiently transfected rat chondrosarcoma
(RCS) cells and mouse primary chondrocytes but not in 10T1/2 fibroblasts.
They also directed cartilage specificity in transgenic mouse embryos. These
48 bp include two 11-bp inverted repeats with only one mismatch. Tandem
copies of an 18-bp element containing the 3' repeat strongly enhanced
promoter activity in RCS cells and chondrocytes but not in fibroblasts.
Transgenic mice harboring 12 copies of this 18-mer expressed luciferase in
ribs and vertebrae and in isolated chondrocytes but not in noncartilaginous
tissues except skin and brain. In gel retardation assays, an RCS
cell-specific protein and another closely related protein expressed only in
RCS cells and primary chondrocytes bound to a 10-bp sequence within the
18-mer. Mutations in these 10 bp abolished activity of the multimerized
18-bp enhancer, and deletion of these 10 bp abolished enhancer activity of
465- and 231-bp intron 1 segments. This sequence contains a low-affinity
binding site for POU domain proteins, and competition experiments with a
high-affinity POU domain binding site strongly suggested that the
chondrocyte proteins belong to this family. Together, our results indicate
that an 18-bp sequence in Col2a1 intron 1 controls chondrocyte expression
and suggest that RCS cells and chondrocytes contain specific POU domain
proteins involved in enhancer activity.
Copyright © 1996, American Society for Microbiology
An 18-base-pair sequence in the mouse proalpha1(II) collagen gene is sufficient for expression in cartilage and binds nuclear proteins that are selectively expressed in chondrocytes
Department of Molecular Genetics, The University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
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