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Updated: May 16, 2026
Culture of Murine Embryonic Metatarsals: A Physiological Model of Endochondral Ossification
Published on: December 3, 2016
Toward an understanding of the short bone phenotype associated with multiple osteochondromas
Kevin B Jones1, Manasi Datar, Sandhya Ravichandran
1Sarcoma Services, Department of Orthopaedics and Center for Children's Cancer Research, Huntsman Cancer Institute, University of Utah School of Medicine, Salt Lake City, UT, USA.
Abstract:
Individuals with multiple osteochondromas (MO) demonstrate shortened long bones. Ext1 or Ext2 haploinsufficiency cannot recapitulate the phenotype in mice. Loss of heterozygosity for Ext1 may induce shortening by steal of longitudinal growth into osteochondromas or by a general derangement of physeal signaling. We induced osteochondromagenesis at different time points during skeletal growth in a mouse genetic model, then analyzed femora and tibiae at 12 weeks using micro-CT and a point-distribution-based shape analysis. Bone lengths and volumes were compared. Metaphyseal volume deviations from normal, as a measure of phenotypic widening, were tested for correlation with length deviations. Mice with osteochondromas had shorter femora and tibiae than controls, more consistently when osteochondromagenesis was induced earlier during skeletal growth. Volumetric metaphyseal widening did not correlate with longitudinal shortening, although some of the most severe shortening was in bones with abundant osteochondromas. Loss of heterozygosity for Ext1 was sufficient to drive bone shortening in a mouse model of MO, but shortening did not correlate with osteochondroma volumetric growth. While a steal phenomenon seems apparent in individual cases, some other mechanism must also be capable of contributing to the short bone phenotype, independent of osteochondroma formation. Clones of chondrocytes lacking functional heparan sulfate must blunt physeal signaling generally, rather than stealing growth potential focally.
Insights
Multiple osteochondromas (MO) cause short long bones in mice. Loss of Ext1 function shortens bones, but not solely by growth diversion into tumors, suggesting broader growth plate signaling disruption.
Area of Science:
- Skeletal biology
- Genetics
- Developmental biology
Background:
- Multiple osteochondromas (MO) are characterized by shortened long bones.
- Existing mouse models of Ext1 or Ext2 haploinsufficiency do not fully replicate this phenotype.
- Loss of heterozygosity for Ext1 is hypothesized to cause shortening via growth diversion or disrupted physeal signaling.
Purpose of the Study:
- To investigate the mechanisms underlying long bone shortening in a mouse model of MO.
- To determine the relationship between osteochondroma formation and bone length reduction.
- To elucidate the role of Ext1 loss of heterozygosity in skeletal growth abnormalities.
Main Methods:
- Induced osteochondromagenesis at various developmental stages in a mouse genetic model.
- Analyzed femora and tibiae at 12 weeks using micro-computed tomography (micro-CT) and shape analysis.
- Compared bone lengths, volumes, and metaphyseal volume deviations between affected and control mice.
Main Results:
- Mice with MO exhibited shorter femora and tibiae compared to controls, particularly when osteochondromagenesis occurred earlier in skeletal development.
- Volumetric metaphyseal widening did not correlate with longitudinal shortening.
- Ext1 loss of heterozygosity induced bone shortening independently of osteochondroma volume.
Conclusions:
- Loss of Ext1 function is sufficient to cause bone shortening in a mouse model of MO.
- The short bone phenotype is not solely explained by a 'steal' phenomenon where growth is diverted into osteochondromas.
- Disruption of physeal signaling due to loss of functional heparan sulfate in chondrocytes likely contributes to generalized growth blunting.
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