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J. Cell Biol.,
Volume 140, Number 2, January 26, 1998 419-430




* Department of Biochemistry, Thrombospondin (TSP) 2, and its close relative TSP1, are extracellular proteins whose functions
are complex, poorly understood, and controversial. In
an attempt to determine the function of TSP2, we disrupted the Thbs2 gene by homologous recombination in embryonic stem cells, and generated TSP2-null mice
by blastocyst injection and appropriate breeding of mutant animals. Thbs2
Department of Medicine, University of Washington, Seattle, Washington 98195; § Zymogenetics,
Inc., Seattle, Washington 98105;
Department of Pathology, Anatomy, and Cell Biology, Jefferson Medical College, Thomas
Jefferson University, Philadelphia, Pennsylvania 19107; and ¶ Clinical Neuroscience Branch, National Institute of Mental Health,
National Institutes of Health, Bethesda, Maryland 20892
/
mice were produced with the
expected Mendelian frequency, appeared overtly normal, and were fertile. However, on closer examination, these mice displayed a wide variety of abnormalities.
Collagen fiber patterns in skin were disordered, and abnormally large fibrils with irregular contours were observed by electron microscopy in both skin and tendon.
As a functional correlate of these findings, the skin was
fragile and had reduced tensile strength, and the tail
was unusually flexible. Mutant skin fibroblasts were defective in attachment to a substratum. An increase in
total density and in cortical thickness of long bones was
documented by histology and quantitative computer tomography. Mutant mice also manifested an abnormal
bleeding time, and histologic surveys of mouse tissues, stained with an antibody to von Willebrand factor,
showed a significant increase in blood vessels. The basis
for the unusual phenotype of the TSP2-null mouse
could derive from the structural role that TSP2 might
play in collagen fibrillogenesis in skin and tendon. However, it seems likely that some of the diverse manifestations of this genetic disorder result from the ability
of TSP2 to modulate the cell surface properties of mesenchymal cells, and thus, to affect cell functions such as
adhesion and migration.
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