Molecular analysis of a human PAX6 homeobox mutant.
Pax6 controls eye, pancreas and brain morphogenesis. In humans, heterozygous PAX6 mutations cause aniridia and various other congenital eye abnormalities. Most frequent PAX6 missense mutations are located in the paired domain (PD), while very few missense mutations have been identified in the homeodomain (HD). In the present report, we describe a molecular analysis of the human PAX6 R242T missense mutation, which is located in the second helix of the HD. It was identified in a male child with partial aniridia in the left eye, presenting as a pseudo-coloboma. Gel-retardation assays revealed that the mutant HD binds DNA as well as the wild-type HD. In addition, the mutation does not modify the DNA-binding properties of the PD. Cell transfection assays indicated that the steady-state levels of the full length mutant protein are higher than those of the wild-type one. In cotransfection assays a PAX6 responsive promoter is activated to a higher extent by the mutant protein than by the wild-type protein. In vitro limited proteolysis assays indicated that the presence of the mutation reduces the sensitivity to trypsin digestion. Thus, we suggest that the R242T human phenotype could be due to abnormal increase of PAX6 protein, in keeping with the reported sensitivity of the eye phenotype to increased PAX6 dosage.
Dipartimento di Scienze e Tecnologie Biomediche, Università di Udine, Udine, Italy.
Angela Valentina
AV
D'Elia
Cinzia
C
Puppin
Lucia
L
Pellizzari
Annalisa
A
Pianta
Elisa
E
Bregant
Renata
R
Lonigro
Gianluca
G
Tell
Federico
F
Fogolari
Veronica
V
van Heyningen
Giuseppe
G
Damante
D000818:Animals; D015783:Aniridia / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism; D018628:Gene Dosage / Q000235:genetics; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D020125:Mutation, Missense; D038081:Organogenesis / Q000235:genetics; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism
D005136:Eye Proteins; D018398:Homeodomain Proteins; D000071841:PAX6 Transcription Factor; C000605730:PAX6 protein, human; D051761:Paired Box Transcription Factors; C000605732:Pax6 protein, mouse; D012097:Repressor Proteins; D004247:DNA