Homeobox genes d11–d13 and a13 control mouse autopod cortical bone and joint formation
Pablo Villavicencio-Lorini, … , Jochen Hecht, Stefan Mundlos
Pablo Villavicencio-Lorini, … , Jochen Hecht, Stefan Mundlos
Published May 10, 2010
Citation Information: J Clin Invest. 2010;120(6):1994-2004. https://doi.org/10.1172/JCI41554.
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Homeobox genes d11–d13 and a13 control mouse autopod cortical bone and joint formation

Abstract

The molecular mechanisms that govern bone and joint formation are complex, involving an integrated network of signaling pathways and gene regulators. We investigated the role of Hox genes, which are known to specify individual segments of the skeleton, in the formation of autopod limb bones (i.e., the hands and feet) using the mouse mutant synpolydactyly homolog (spdh), which encodes a polyalanine expansion in Hoxd13. We found that no cortical bone was formed in the autopod in spdh/spdh mice; instead, these bones underwent trabecular ossification after birth. Spdh/spdh metacarpals acquired an ovoid shape and developed ectopic joints, indicating a loss of long bone characteristics and thus a transformation of metacarpals into carpal bones. The perichondrium of spdh/spdh mice showed abnormal morphology and decreased expression of Runt-related transcription factor 2 (Runx2), which was identified as a direct Hoxd13 transcriptional target. Hoxd11–/–Hoxd12–/–Hoxd13–/– triple-knockout mice and Hoxd13–/–Hoxa13+/– mice exhibited similar but less severe defects, suggesting that these Hox genes have similar and complementary functions and that the spdh allele acts as a dominant negative. This effect was shown to be due to sequestration of other polyalanine-containing transcription factors by the mutant Hoxd13 in the cytoplasm, leading to their degradation. These data indicate that Hox genes not only regulate patterning but also directly influence bone formation and the ossification pattern of bones, in part via Runx2.

Authors

Pablo Villavicencio-Lorini, Pia Kuss, Julia Friedrich, Julia Haupt, Muhammed Farooq, Seval Türkmen, Denis Duboule, Jochen Hecht, Stefan Mundlos

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Figure 4

Homeotic transformation in Hox mutant mice.

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Homeotic transformation in Hox mutant mice. (A) Histology at P7 of WT an...
(A) Histology at P7 of WT and spdh/spdh forelimbs. Mutant metacarpal bones show mineralized cartilage (black) similar to WT carpal bones or secondary ossification centers. Mutant metacarpals have adopted a round carpal-like shape with joint-like gaps. c, carpal; cb, cortical bone; so, secondary ossification center. (B) Higher magnification (×200) of metacarpal bones. WT cortical bone of metacarpals (black) is separated by connective tissue (pink). In mutant mice, carpal bones are surrounded by cartilage. This cartilage has a similar morphology to that in the joints of WT carpal bones. (C) In situ hybridization against Col2a1. At E14.5, Col2a1 is expressed throughout the cartilaginous anlage. At P7, WT (composited view) Col2a1 is expressed around the carpal bones and secondary ossification centers marking the joint cartilage. In spdh/spdh forelimbs, Col2a1 is expressed in a narrow band around the metacarpals similar to that seen in WT carpals. (D) X-rays of a patient with synpolydactyly. Carpals (c) have a round shape; metacarpals (m) are long bones, with cortical bones in the shaft region. In the patient, metacarpal bones have adopted a carpal-like shape. (E) In situ hybridization of Gdf5 at E12.5 to E16.5. In spdh/spdh limbs, Gdf5 is expressed around the cartilage anlagen. Boxes show magnifications (×250). (F) In situ hybridizations at E14.5 with joint markers Sfrp2, Wnt4, and Dkk3. In all cases, joint expression is lost in spdh/spdh animals; instead, there is an upregulation in perichondrial regions along the metacarpal structures.