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J. Cell Biol.,
Volume 145, Number 5, May 31, 1999 1103-1115
* Department of Biochemistry and Molecular Biology, University of Texas, M.D. Anderson Cancer Center, Houston, Texas
77030; Expression of the basement membrane
heparan sulfate proteoglycan (HSPG), perlecan (Pln),
mRNA, and protein has been examined during murine
development. Both Pln mRNA and protein are highly expressed in cartilaginous regions of developing mouse
embryos, but not in areas of membranous bone formation. Initially detected at low levels in precartilaginous
areas of d 12.5 embryos, Pln protein accumulates in
these regions through d 15.5 at which time high levels
are detected in the cartilage primordia. Laminin and collagen type IV, other basal lamina proteins commonly
found colocalized with Pln, are absent from the cartilage primordia. Accumulation of Pln mRNA, detected
by in situ hybridization, was increased in d 14.5 embryos. Cartilage primordia expression decreased to levels similar to that of the surrounding tissue at d 15.5. Pln accumulation in developing cartilage is preceded by
that of collagen type II. To gain insight into Pln function
in chondrogenesis, an assay was developed to assess the
potential inductive activity of Pln using multipotential
10T1/2 murine embryonic fibroblast cells. Culture on
Pln, but not on a variety of other matrices, stimulated
extensive formation of dense nodules reminiscent of embryonic cartilaginous condensations. These nodules
stained intensely with Alcian blue and collagen type II
antibodies. mRNA encoding chondrocyte markers including collagen type II, aggrecan, and Pln was elevated
in 10T1/2 cells cultured on Pln. Human chondrocytes that otherwise rapidly dedifferentiate during in vitro
culture also formed nodules and expressed high levels
of chondrocytic marker proteins when cultured on Pln.
Collectively, these studies demonstrate that Pln is not
only a marker of chondrogenesis, but also strongly potentiates chondrogenic differentiation in vitro.
Department of Basic Science, University of Texas, Dental Branch, Houston, Texas 77030; and § Department of Pediatrics,
University of Texas Medical School, Houston, Texas 77030
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