[101] Zebrafish Model for Studies on Bone Defects in Multiple Osteochondromas

M Wiweger, H Roehl, PCW Hogendoorn. LUMC, Leiden, Netherlands; University of Sheffield, Sheffield, United Kingdom

Background: Multiple Osteochondromas (MO) previously known as Hereditary Multiple Exostosis (HME) is caused by a mutation in Exostosins (EXT) genes, EXT1 or EXT2. MO is characterized by the formation of multiple cartilaginous bone outgrowths near growth plates. However, it seems that MO phenotype is not restricted to osteochondromas. In order to find more information about MO, we use zebrafish mutant called dackel (dak) that is mutated in a homologue of the EXT2 gene. dak/ext2 mutant is the only available vertebrate that completes embryo development when homozygous for mutation in an ext and displays various phenotypical changes e.g. similar chondrocyte organization as this in osteochondromas.

We have recently shown that mutation in dak/ext2 does not affect cartilage differentiation but it disrupts cartilage morphogenesis and bone development (Clement et al., 2008). As not much is know about bone condition in MO, we examined skeletal changes in juvenile and adult skeletons in dak/ext2(+/-) mutants and investigated involvement of FGF signaling in MO.
Design: Zebrafish heterozygous mutants for dak/ext2, ace/fgf8 and their siblings were raised to adolescence, harvested, fixed in 4% PFA and stained with Alizarin red and Alcian blue. Juvenile dak/ext2 mutants were subjected to TRAP staining. Skeletons were analyzed under dissecting-scope. Each group had minimum 10 fish. Experiments were repeated two times with similar results.
Results: In 20% of dak/ext2 and ace/fgf8 mutants deformities similar to those that are well recognized in MO patients i.e. osteochondromas-like outgrowths, bone curving and bone shortening/thickening were found. Similar deformities were also observed in dermal bones, in both zebrafish mutants. TRAP staining indicated altered osteoclast function in dak/ext2 mutants.
Conclusions: Our findings from zebrafish model indicate that MO patients can have general skeletal problems. Deformities of endochondral bones are more likely to result from malformations of cartilage templates whereas the presence of defects in intramembranous bones is most likely due to osteoclast dysfunction. Similarities between bone phenotype of dak/ext2 and ace/fgf8 mutants indicate that impaired FGF signaling might contribute to bone defects in MO.
Category: Bone & Soft Tissue

Tuesday, March 10, 2009 9:30 AM

Poster Session III # 12, Tuesday Morning