Potential novel mechanism for Axenfeld-Rieger syndrome: deletion of a distant region containing regulatory elements of PITX2.
OBJECTIVE
Mutations in PITX2 are associated with Axenfeld-Rieger syndrome (ARS), which involves ocular, dental, and umbilical abnormalities. Identification of cis-regulatory elements of PITX2 is important to better understand the mechanisms of disease.


METHODS
Conserved noncoding elements surrounding PITX2/pitx2 were identified and examined through transgenic analysis in zebrafish; expression pattern was studied by in situ hybridization. Patient samples were screened for deletion/duplication of the PITX2 upstream region using arrays and probes.


RESULTS
Zebrafish pitx2 demonstrates conserved expression during ocular and craniofacial development. Thirteen conserved noncoding sequences positioned within a gene desert as far as 1.1 Mb upstream of the human PITX2 gene were identified; 11 have enhancer activities consistent with pitx2 expression. Ten elements mediated expression in the developing brain, four regions were active during eye formation, and two sequences were associated with craniofacial expression. One region, CE4, located approximately 111 kb upstream of PITX2, directed a complex pattern including expression in the developing eye and craniofacial region, the classic sites affected in ARS. Screening of ARS patients identified an approximately 7600-kb deletion that began 106 to 108 kb upstream of the PITX2 gene, leaving PITX2 intact while removing regulatory elements CE4 to CE13.


CONCLUSIONS
These data suggest the presence of a complex distant regulatory matrix within the gene desert located upstream of PITX2 with an essential role in its activity and provides a possible mechanism for the previous reports of ARS in patients with balanced translocations involving the 4q25 region upstream of PITX2 and the current patient with an upstream deletion.
Volkmann
Bethany A
BA
Department of Pediatrics and Children's Research Institute, Medical College of Wisconsin, Milwaukee, Wisconsin, USA.
Zinkevich
Natalya S
NS
Mustonen
Aki
A
Schilter
Kala F
KF
Bosenko
Dmitry V
DV
Reis
Linda M
LM
Broeckel
Ulrich
U
Link
Brian A
BA
Semina
Elena V
EV
D000818:Animals; D030801:Animals, Genetically Modified; D000869:Anterior Eye Segment / Q000002:abnormalities / Q000473:pathology; D005124:Eye Abnormalities / Q000235:genetics / Q000473:pathology; D015785:Eye Diseases, Hereditary; D017353:Gene Deletion; D020440:Gene Duplication; D015870:Gene Expression; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D017403:In Situ Hybridization; D007223:Infant; D008297:Male; D009154:Mutation; D010957:Plasmids; D050436:Regulatory Elements, Transcriptional / Q000235:genetics*; D017384:Sequence Deletion; D014157:Transcription Factors / Q000235:genetics*; D015027:Zebrafish; D000097577:Homeobox Protein PITX2
D018398:Homeodomain Proteins; D014157:Transcription Factors; D000097577:Homeobox Protein PITX2