Conditional deletion of Indian hedgehog from collagen type 2α1‐expressing cells results in abnormal endochondral bone formation

MS Razzaque, DW Soegiarto, D Chang… - The Journal of …, 2005 - Wiley Online Library
MS Razzaque, DW Soegiarto, D Chang, F Long, B Lanske
The Journal of Pathology: A Journal of the Pathological Society of …, 2005Wiley Online Library
Indian hedgehog (Ihh) is actively involved in endochondral bone formation. Although
expression of Ihh is mostly restricted to pre‐hypertrophic chondrocytes, the role of
chondrocyte‐derived Ihh in endochondral bone formation is not completely understood. To
address such unresolved issues, we used the Cre/loxP approach to generate mice
(Col2α1Cre; Ihhd/Ihhd) in which the Ihh gene was selectively ablated from collagen type II
expressing cells. Mutant mice were born with the expected ratio of Mendelian inheritance …
Abstract
Indian hedgehog (Ihh) is actively involved in endochondral bone formation. Although expression of Ihh is mostly restricted to pre‐hypertrophic chondrocytes, the role of chondrocyte‐derived Ihh in endochondral bone formation is not completely understood. To address such unresolved issues, we used the Cre/loxP approach to generate mice (Col2α1Cre; Ihhd/Ihhd) in which the Ihh gene was selectively ablated from collagen type II expressing cells. Mutant mice were born with the expected ratio of Mendelian inheritance, but died shortly after birth and were smaller in size, exhibiting malformed and retarded growth of limbs with severe skeletal deformities. Alizarin red S staining showed abnormal mineralization of axial and appendicular bones. Histological analysis of mutant long bones revealed abnormal endochondral bone formation with loss of a normal growth plate. In addition, in vivo bromo‐deoxyuridine (BrdU) labelling showed a marked decrease in chondrocyte proliferation. A delay in chondrocyte hypertrophy in Col2α1Cre; Ihhd/Ihhd mice was detected by the expression of collagen type X and osteopontin, using in situ hybridization. Furthermore, there was no expression of bone markers such as collagen type I, bone Gla protein, Runx2/Cbfa1 or PTH‐R in the perichondrium of mutant mice, indicating the absence of osteoblasts from endochondral bones. Thus, selective loss of chondrocyte‐derived Ihh recapitulated the defects in Ihh−/− animals, providing direct in vivo evidence that Ihh not only regulates chondrocyte proliferation and differentiation but also exerts effects on osteoblast differentiation. Understanding the exact functions of the molecules involved in endochondral bone formation will form the basis for further study to determine the molecular mechanisms of skeletal diseases involving various cellular components of bone. Copyright © 2005 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
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