alpha A-crystallin is expressed in non-ocular tissues.
alpha-Crystallin, the predominant structural protein of the ocular lens, has been considered to be composed of two subunits, alpha A-crystallin and alpha B-crystallin. Of these two, alpha B-crystallin has been previously shown to be an extralenticular protein while alpha A-crystallin has been considered to be a lens-specific polypeptide. Using an antiserum directed against an N-terminal peptide of alpha-crystallin, we have detected a 20-kDa protein in various rat tissues including the brain, liver, lung, spleen, skin, and small intestine and in a number of established epithelial and fibroblast cell lines. PCR analysis of poly(A)-enriched RNA and Southern blot analysis indicated the presence of alpha A-crystallin mRNA sequences in different non-lenticular tissues. Among the non-ocular tissues examined, spleen showed the highest levels of alpha A-crystallin protein and mRNA. The identity of alpha A-crystallin sequences in the spleen was established by cloning and sequencing a polymerase chain reaction-amplified region of alpha A-crystallin mRNA. Sequences derived from spleen and eye revealed almost 100% identity at the nucleotide level. Interestingly, alpha A-crystallin and alpha B-crystallin seem to exist in an inverse quantitative relationship in the spleen and the heart, the two non-ocular tissues where they show highest concentrations, respectively. The known conserved evolution of alpha A-crystallin and the definitive demonstration of the non-ocular expression of this polypeptide suggest important non-crystallin functions for this protein.
Srinivasan
A N
AN
Jules Stein Eye Institute, UCLA School of Medicine 90024-7008.
Nagineni
C N
CN
Bhat
S P
SP
D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D003459:Crystallins / Q000032:analysis / Q000096:biosynthesis / Q000235:genetics*; D004591:Electrophoresis, Polyacrylamide Gel; D005333:Fetus; D015870:Gene Expression; D006801:Humans; D007106:Immune Sera; D015151:Immunoblotting; D007908:Lens, Crystalline / Q000502:physiology*; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009838:Oligodeoxyribonucleotides; D009928:Organ Specificity; D016133:Polymerase Chain Reaction / Q000379:methods; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012689:Sequence Homology, Nucleic Acid; D013154:Spleen / Q000502:physiology*
D003459:Crystallins; D007106:Immune Sera; D046911:Macromolecular Substances; D009838:Oligodeoxyribonucleotides; D012333:RNA, Messenger