A G220V substitution within the N-terminal transcription regulating domain of HOXD13 causes a variant synpolydactyly phenotype.
The 5' members of the HoxD gene cluster (paralogous groups 9-13) are crucial for correct vertebrate limb patterning. Mutations in the HOXD13 gene have been found to cause synpolydactyly (SPD) and other limb malformations in human. We report the identification in a Greek family of a variant form of SPD caused by a novel missense mutation that substitutes glycine for valine in position 220 (G220V) of HOXD13. This mutation represents the first substitution of an amino acid located outside of the HOXD13 homeodomain that causes autopodal limb malformations. We have characterized this mutation at the molecular level and found that the G220V substitution causes a significant impairment of the capacity of HOXD13 to bind DNA and regulate transcription. HOXD13(G220V) was found to be deficient in both activating and repressing transcription through HOXD13-responsive regulatory elements. In accordance with these results, a comparison of the activities of HOXD13 and HOXD13(G220V) in vivo, using retrovirus-mediated misexpression in developing chick limbs, showed that the G220V mutation impairs the capacity of HOXD13 to perturb the development of proximal limb skeletal elements and to ectopically activate the transcription of the Hand2 target gene. We moreover show that the G220V mutation compromises the stability of the HOXD13 protein within cells and causes its partial accumulation in the cytosol in the form of subtle aggregates. Taken together, our results establish that the G220V substitution does not produce a dominant-negative effect or a gain-of-function, but represents a dominant loss-of-function mutation revealing haploinsufficiency of HOXD13 in human.
Fantini
Sebastian
S
Department of Animal Biology, University of Modena and Reggio Emilia, Via Campi 213/D, 41100 Modena, Italy.
Vaccari
Giulia
G
Brison
Nathalie
N
Debeer
Philippe
P
Tylzanowski
Przemko
P
Zappavigna
Vincenzo
V
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D019556:COS Cells; D045744:Cell Line, Tumor; D002645:Chickens; D002522:Chlorocebus aethiops; D018398:Homeodomain Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D017880:Limb Deformities, Congenital / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D020125:Mutation, Missense; D010375:Pedigree; D010641:Phenotype; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
C513184:HOXD13 protein, human; D018398:Homeodomain Proteins; D014157:Transcription Factors