OPA3A and OPA3B structure and expression.
(A) Schematic of the OPA3 locus on chromosome 19q13.32 (not to scale). Intron and exon sizes are indicated. Neighboring upstream and downstream genes are GPR4 and VASP, respectively. A LINE-1 transposon (L1MC4), located about 24-kb upstream of exon 2, may have led to formation of exon 3 by segmental duplication.
(B) Expression analysis of OPA3A (left) and OPA3B (right) using a multiple human tissue cDNA panel.
(C) Expression of OPA3A and OPA3B in cDNA of normal (C1 and C2) and 3-MGCA type III fibroblasts P1 and P2, carrying homozygous c.143-1G>C and c.320-337del mutations, respectively.
(D) Real-time quantitative PCR analysis of OPA3A and OPA3B transcripts in 3-MGCA type III (P1) fibroblasts compared to normal fibroblasts. Exon-specific primer-probe combinations showed a 5.8 fold (p<0.0001) up-regulation for exon 1 (ex1), a 2.7 fold (p=0.034) down-regulation of exon 2 (ex2; representing OPA3A), and a 4.8 fold (p<0.0001) up-regulation of exon 3 (ex3; representing OPA3B) (n=3).
(E) Amino acid sequence alignment of OPA3A and OPA3B. The N-terminal amino acids encoded by exon 1 (bold) are shared by both proteins and contain a potential mitochondrial leader sequence (amino acids 1-18, underlined) and mitochondrial targeting signal NRIKE (amino acids 25-29, underlined). The potential C-terminal peroxisomal sorting signals SKK for OPA3A and SEK for OPA3B are gray shaded and underlined. Over the entire protein, OPA3A and OPA3B are 77.6% homologous; their C-terminal sequences contain 41 mismatches (printed in bold italic in the OPA3B sequence).