2009 Conference abstract
Osteochondromagenesis: somatic loss of heterozygosity modeled via Cre-mediated inversion of the second exon of
Ext1 in chondrocytes
§†Kevin B. Jones, MD; ◊Virginia Piombo, BS; *Charles Searby, BS; †Gail Kurriger, BS; ■Florian Grabellus, MD; ‡Peter Roughley,
PhD; †Jose A. Morcuende, MD, MS; †Joseph A. Buckwalter, MD, MS; ☼Mario R. Capecchi, PhD; ◊Andrea Vortkamp, PhD;
*Val C. Sheffield, MD, PhD
§Department of Orthopaedics and Huntsman Cancer Institute, ☼Department of Human Genetics and Howard Hughes Medical
Institute, University of Utah. †Department of Orthopaedics and Rehabilitation, and *Department of Pediatrics, Division of Medical
Genetics, Howard Hughes Medical Institute, University of Iowa. ◊Department for Biology and Geography and ■Institute for
Pathology and Neuropathology, University of Duisburg-Essen, Essen Germany. ‡Shriner’s Hospital Research Institute, Montreal,
Quebec, Canada.
Multiple hereditary exostoses (MHE) is caused by heterozygosity for mutations in EXT1 or EXT2. Osteochondroma pathogenesis
in this disorder remains elusive. Mice homozygous null for homologous Ext1 or Ext2 die prenatally; only rarely will a
heterozygote form a rib osteochondroma-like excrescence. Origin of osteochondromas in the physeal chondrocytes or adjacent
perichondrium is also unclear.
Gene-targeting generated a unique conditional allele of Ext1 with trans-orientation loxP sites flanking exon 2. Mice bearing this
Ext1e2neofl were crossed with mice bearing transgenic Cre-recombinase driven by a doxycycline-inducible collagen IIa1 promoter
(Col2-rtTA-Cre). Doxycyline was administered during week 2 of life. Mice were sacrificed for phenotypic analysis at 4, 6, and 10
weeks. Phenotypic analysis included histology of ribs and knees and microCT. Crossing to mice bearing Cre-recombinase driven
by Osterix expression and activated by tamoxifen (Osx-CreERT) at P8 tested competing cells of origin.
PCR from cartilage containing tissues demonstrated both forward- and reverse-orientation exon 2 in Ext1e2neofl/e2neofl;Col2-
rtTA-Cre mice after receiving doxycycline. Homozygotes lacking Cre and heterozygotes with Cre had no demonstrable
phenotype. Homozygotes with induced Cre consistently developed numerous osteochondromas. Ext1e2neofl/e2neofl;Osx-
CreERT mice, in contrast, formed no osteochondromas.
Reversible Cre-mediated inversion of a trans-floxed genomic fragment results in a 50:50 distribution of forward and reverse
orientation alleles and a small fraction of cells with homozygous disruption. This genetic recapitulation of somatic loss of
heterozygosity of Ext1 in physeal chondrocytes generated numerous osteochondromas, when heterozygosity for a null-allele
failed to. This argues that loss of heterozygosity is critical to the phenotypic expression of MHE. That osteochondromas do not
form when Ext1 disruption is induced in pre-osteoblasts argues for a proliferating chondrocytes as the cell of origin.
Osteochondromagenesis: somatic loss of heterozygosity modeled via Cre-mediated inversion of the second exon of
Ext1 in chondrocytes
§†Kevin B. Jones, MD; ◊Virginia Piombo, BS; *Charles Searby, BS; †Gail Kurriger, BS; ■Florian Grabellus, MD; ‡Peter Roughley,
PhD; †Jose A. Morcuende, MD, MS; †Joseph A. Buckwalter, MD, MS; ☼Mario R. Capecchi, PhD; ◊Andrea Vortkamp, PhD;
*Val C. Sheffield, MD, PhD
§Department of Orthopaedics and Huntsman Cancer Institute, ☼Department of Human Genetics and Howard Hughes Medical
Institute, University of Utah. †Department of Orthopaedics and Rehabilitation, and *Department of Pediatrics, Division of Medical
Genetics, Howard Hughes Medical Institute, University of Iowa. ◊Department for Biology and Geography and ■Institute for
Pathology and Neuropathology, University of Duisburg-Essen, Essen Germany. ‡Shriner’s Hospital Research Institute, Montreal,
Quebec, Canada.
Multiple hereditary exostoses (MHE) is caused by heterozygosity for mutations in EXT1 or EXT2. Osteochondroma pathogenesis
in this disorder remains elusive. Mice homozygous null for homologous Ext1 or Ext2 die prenatally; only rarely will a
heterozygote form a rib osteochondroma-like excrescence. Origin of osteochondromas in the physeal chondrocytes or adjacent
perichondrium is also unclear.
Gene-targeting generated a unique conditional allele of Ext1 with trans-orientation loxP sites flanking exon 2. Mice bearing this
Ext1e2neofl were crossed with mice bearing transgenic Cre-recombinase driven by a doxycycline-inducible collagen IIa1 promoter
(Col2-rtTA-Cre). Doxycyline was administered during week 2 of life. Mice were sacrificed for phenotypic analysis at 4, 6, and 10
weeks. Phenotypic analysis included histology of ribs and knees and microCT. Crossing to mice bearing Cre-recombinase driven
by Osterix expression and activated by tamoxifen (Osx-CreERT) at P8 tested competing cells of origin.
PCR from cartilage containing tissues demonstrated both forward- and reverse-orientation exon 2 in Ext1e2neofl/e2neofl;Col2-
rtTA-Cre mice after receiving doxycycline. Homozygotes lacking Cre and heterozygotes with Cre had no demonstrable
phenotype. Homozygotes with induced Cre consistently developed numerous osteochondromas. Ext1e2neofl/e2neofl;Osx-
CreERT mice, in contrast, formed no osteochondromas.
Reversible Cre-mediated inversion of a trans-floxed genomic fragment results in a 50:50 distribution of forward and reverse
orientation alleles and a small fraction of cells with homozygous disruption. This genetic recapitulation of somatic loss of
heterozygosity of Ext1 in physeal chondrocytes generated numerous osteochondromas, when heterozygosity for a null-allele
failed to. This argues that loss of heterozygosity is critical to the phenotypic expression of MHE. That osteochondromas do not
form when Ext1 disruption is induced in pre-osteoblasts argues for a proliferating chondrocytes as the cell of origin.
| Dr. Kevin B. Jones |
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Power Point presentation at during the 2008 Connective Tissue Oncology Society conference Click Here
(Knock Mice Model presentation)
Osteochondromagenesis: Loss of heterozygosity modeled via Cre-mediated inversion of the second exon of Ext1 in
chondrocytes
(Knock Mice Model presentation)
Osteochondromagenesis: Loss of heterozygosity modeled via Cre-mediated inversion of the second exon of Ext1 in
chondrocytes
Of hedgehogs and hereditary bone tumors: re-examination of the pathogenesis of osteochondromas.
Jones KB, Morcuende JA.
Iowa Orthop J. 2003;23:87-95. Review.
To read this Full Text publication Click Here
Jones KB, Morcuende JA.
Iowa Orthop J. 2003;23:87-95. Review.
To read this Full Text publication Click Here
Biological Sciences - Developmental Biology:
A mouse model of osteochondromagenesis from clonal inactivation of Ext1 in chondrocytes
Kevin B. Jones, Virginia Piombo, Charles Searby, Gail Kurriger, Baoli Yang, Florian Grabellus, Peter J. Roughley, Jose A.
Morcuende, Joseph A. Buckwalter, Mario R. Capecchi, Andrea Vortkamp, and Val C. Sheffield
PNAS published online doi:10.1073/pnas.0910875107
A mouse model of osteochondromagenesis from clonal inactivation of Ext1 in chondrocytes
Kevin B. Jones, Virginia Piombo, Charles Searby, Gail Kurriger, Baoli Yang, Florian Grabellus, Peter J. Roughley, Jose A.
Morcuende, Joseph A. Buckwalter, Mario R. Capecchi, Andrea Vortkamp, and Val C. Sheffield
PNAS published online doi:10.1073/pnas.0910875107
Kevin B. Jones, M.D.
Sarcoma Services
Huntsman Cancer Institute
and Primary Children's Medical Center
Department of Orthopaedics
University of Utah
Salt Lake City, Utah
Website: medicine.utah.edu/orthopaedics/physicians/faculty/jones.htm
Sarcoma Services
Huntsman Cancer Institute
and Primary Children's Medical Center
Department of Orthopaedics
University of Utah
Salt Lake City, Utah
Website: medicine.utah.edu/orthopaedics/physicians/faculty/jones.htm
| Photo's taken during the Third International MHE Research Conference |
Dr. Jones serves on the Scientific and Medical Advisory Board of the MHE Research Foundation
Publications authored by Dr. Jones
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List of Publications via PubMed
(NIH National Library of Medicine)
Publications authored by Dr. Jones
Click the tab and a window will appear.
List of Publications via PubMed
(NIH National Library of Medicine)
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Click here to verify.# HON Conduct 282463 and is the patient support link on the US Government Genetics Home Reference (http://ghr.nlm.nih.gov)
website, also linked for Patient Information on The Diseases Database a cross-referenced index of human disease, as well as the
Intute: health & life sciences a free online service providing access to the very best Web resources for education and research located in the UK
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| Dr. Kevin B. Jones has recently authored the book "What Doctors Cannot Tell You: Clarity, Confidence and Uncertainty in Medicine" Dr. Jones serves on the Scientific and Medical Advisory Board of our Foundation. We would like to thank Dr. Jones for all of his efforts on behalf of patients. |
