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 1

Skeletal phenotype of Hox mutant mice.

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Skeletal phenotype of Hox mutant mice. (A) Skeletal preparations of post...
(A) Skeletal preparations of postnatal stages P0, P4, P7, and P14 of WT, spdh/spdh, and Hoxd11,12,13del/del (Δd11-d13) mice. Cartilage stained with Alcian Blue, bone with Alizarin Red. Note additional digit-like structures, a severe delay in ossification, and missing joints in mutant mice. (B) Histology (von Kossa) of postnatal stages P0, P7, and P14 of WT, spdh/spdh, and Hoxd11,12,13del/del (Δd11-d13) metacarpals. Mineralized regions are black, counterstaining with Toluidine Blue and Picro Fuchsin Red. At P0, WT mice show both cortical (C) and trabecular bone (tb) and adjacent growth plates (gp). In mutant mice, mineralization and hypertrophic chondrocytes are completely missing. At P7 in WT, secondary ossification centers are visible at the distal ends of metacarpals. In mutant mice, hypertrophic chondrocytes and mineralized cartilage are present but no cortical bone. At P14 in WT, mineralized cartilage of secondary ossification centers has been replaced by trabecular bone; cortical bone has expanded. In spdh/spdh and Hoxd11,12,13del/del (Δd11–d13) mutants, growth plates are disorganized; mineralized regions have partly been replaced by trabecular bone. No cortical bone is present. Original magnification, ×200. (C) Skeletal preparations at P0 and P7, histology of metacarpals at P7 of Hoxd13–/–, Hoxd13–/–; Hoxa13+/–, and spdh/spdh; Hoxa13+/– mutant mice. Hoxd13–/– mutants exhibit a delay in ossification. Hoxd13–/–; Hoxa13+/– mice show a severe ossification defect at P0 and abnormal bone formation at P7 similar to the spdh/spdh mice. Spdh/spdh; Hoxa13+/– mutant mice show a similar but more severe phenotype.