Characterization of the Crumbs homolog 2 (CRB2) gene and analysis of its role in retinitis pigmentosa and Leber congenital amaurosis.
OBJECTIVE
Mutations in the Crumbs homolog 1 (CRB1) gene cause autosomal recessive retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA). Database searches reveal two other Crumbs homologs on chromosomes 9q33.3 and 19p13.3. The purpose of this study was to characterize the Crumbs homolog 2 (CRB2) gene on 9q33.3, to analyze its expression pattern, and to determine whether mutations in CRB2 are associated with RP and LCA.


METHODS
The CRB2 mRNA and its expression pattern in human tissues were analyzed by reverse transcription-polymerase chain reaction (RT-PCR). The cellular expression of Crb2 in the mouse eye was determined by mRNA in situ hybridizations. The open reading frame and splice junctions of CRB2 were analyzed for mutations by single-strand conformation analysis and direct nucleotide sequencing in 85 RP patients and 79 LCA patients.


RESULTS
The CRB2 gene consists of 13 exons and encodes a 1285 amino acid transmembrane protein. CRB2 is mainly expressed in retina, brain, and kidney. In mouse retina Crb2 expression was detected in all cell layers. Mutation analysis of the CRB2 gene revealed 11 sequence variants leading to an amino acid substitution. Three of them were not identified in control individuals and affect conserved amino acid residues. However, the patients that carry these sequence variants do not have a second sequence variant on the other allele, excluding autosomal recessive inheritance of CRB2 sequence variants as a cause of their disease.


CONCLUSIONS
This study shows that CRB2 sequence variants are not a common cause of autosomal recessive RP and LCA. It is possible that a more complex clinical phenotype is associated with the loss or altered function of CRB2 in humans due to its expression in tissues other than the retina.
van den Hurk
José A J M
JA
Department of Human Genetics, Radboud Univerisity Nijmegen Medical Center, Nijmegen, The Netherlands.
Rashbass
Penny
P
Roepman
Ronald
R
Davis
Jason
J
Voesenek
Krysta E J
KE
Arends
Maarten L
ML
Zonneveld
Marijke N
MN
van Roekel
Marga H G
MH
Cameron
Karen
K
Rohrschneider
Klaus
K
Heckenlively
John R
JR
Koenekoop
Robert K
RK
Hoyng
Carel B
CB
Cremers
Frans P M
FP
den Hollander
Anneke I
AI
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001766:Blindness / Q000151:congenital / Q000235:genetics*; D001921:Brain / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics*; D002899:Chromosomes, Human, Pair 9 / Q000235:genetics*; D004252:DNA Mutational Analysis; D005786:Gene Expression Regulation / Q000502:physiology; D014644:Genetic Variation; D006801:Humans; D017403:In Situ Hybridization; D007668:Kidney / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics*; D051379:Mice; D008808:Mice, Inbred CBA; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames; D018807:Polymorphism, Single-Stranded Conformational; D012333:RNA, Messenger / Q000378:metabolism; D012160:Retina / Q000378:metabolism; D012174:Retinitis Pigmentosa / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
C492531:CRB2 protein, human; D002352:Carrier Proteins; C568885:Crb2 protein, mouse; D008565:Membrane Proteins; D012333:RNA, Messenger