Mutant Hoxd13 induces extra digits in a mouse model of synpolydactyly directly and by decreasing retinoic acid synthesis
Pia Kuss, … , Jochen Hecht, Stefan Mundlos
Pia Kuss, … , Jochen Hecht, Stefan Mundlos
Published December 15, 2008
Citation Information: J Clin Invest. 2009;119(1):146-156. https://doi.org/10.1172/JCI36851.
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Mutant Hoxd13 induces extra digits in a mouse model of synpolydactyly directly and by decreasing retinoic acid synthesis

Abstract

Individuals with the birth defect synpolydactyly (SPD) have 1 or more digit duplicated and 2 or more digits fused together. One form of SPD is caused by polyalanine expansions in homeobox d13 (Hoxd13). Here we have used the naturally occurring mouse mutant that has the same mutation, the SPD homolog (Spdh) allele, and a similar phenotype, to investigate the molecular pathogenesis of SPD. A transgenic approach and crossing experiments showed that the Spdh allele is a combination of loss and gain of function. Here we identify retinaldehyde dehydrogenase 2 (Raldh2), the rate-limiting enzyme for retinoic acid (RA) synthesis in the limb, as a direct Hoxd13 target and show decreased RA production in limbs from Spdh/Spdh mice. Intrauterine treatment with RA restored pentadactyly in Spdh/Spdh mice. We further show that RA and WT Hoxd13 suppress chondrogenesis in mesenchymal progenitor cells, whereas Hoxd13 encoded by Spdh promotes cartilage formation in primary cells isolated from Spdh/Spdh limbs, and that this was associated with increased expression of Sox6/9. Increased Sox9 expression and ectopic cartilage formation in the interdigital mesenchyme of limbs from Spdh/Spdh mice suggest uncontrolled differentiation of these cells into the chondrocytic lineage. Thus, we propose that mutated Hoxd13 causes polydactyly in SPD by inducing extraneous interdigital chondrogenesis, both directly and indirectly, via a reduction in RA levels.

Authors

Pia Kuss, Pablo Villavicencio-Lorini, Florian Witte, Joachim Klose, Andrea N. Albrecht, Petra Seemann, Jochen Hecht, Stefan Mundlos

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Figure 2

Dysregulation of RA pathway in Spdh.

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Dysregulation of RA pathway in Spdh. (A) 2D gel electrophoresis of l...
(A) 2D gel electrophoresis of limb bud tissue (stage E13.5) demonstrated a reduction (63% of WT) of Raldh2 protein levels in Spdh mice (*P < 0.05). (B) Quantification of RA in E13.5 autopod limb tissue. Spdh limbs show a reduction to 57% when compared to WT (**P ≤ 0.005). (C) In situ hybridization against Raldh2 on forelimbs at E12.5 and E13.5 demonstrated a reduction of Raldh2 mRNA in Spdh limbs. In the WT limbs, Raldh2 was expressed in the interdigital space but not the cartilaginous condensations. At E13.5, Raldh2 expression was mainly found in the perichondrium. Expression overlapped with Hoxd13. (D) In situ hybridizations of WT and Spdh forelimbs at E13.5 of RA downstream targets RARβ, dHand, Meis2, and Tbx5. All showed reduced expression in Spdh limbs.