Abundant corneal gelsolin in Zebrafish and the 'four-eyed' fish, Anableps anableps: possible analogy with multifunctional lens crystallins.
The cornea accumulates high proportions (can be up to 50%) of taxon-specific, water-soluble, cytoplasmic proteins (often enzymes) that have been considered analogous to the multifunctional lens crystallins. We have shown that gelsolin (an actin-severing protein) is the major water-soluble corneal protein of the zebrafish (Danio rerio) and the 'four-eyed' fish (Anableps anableps). Each Anableps eye contains one lens, an aquatic ventral cornea with an epithelium comprising 5-7 cell layers, and an air-exposed flatter dorsal cornea with an epithelium comprising >20 cell layers and appreciably enriched with glycogen. Gelsolin accounts for 38 and 21% of the dorsal and ventral cornea, respectively, suggesting that the abundance of gelsolin in the cornea is not incompatible with its function in air. The thicker, glycogen-enriched, air-exposed dorsal cornea may protect against UV irradiation and desiccation. Gelsolin comprises approximately 50% of the 5 cell-layer thick aquatic corneal epithelium of zebrafish. Reported zebrafish ESTs have indicated the presence of a second gelsolin gene in this species. We show by RT-PCR that the abundant corneal gelsolin (also expressed weakly in lens) (C/L-gelsolin) is also expressed in early development and differs from a ubiquitously expressed gelsolin (U-gelsolin) that is not specialized for cornea. Microinjection tests showed that overexpression of C/L-gelsolin dorsalizes the embryo and can lead to axis duplication, while interruption of C/L-gelsolin expression with a specific morpholino oligonucleotide ventralizes the embryo and interferes with brain and eye development. The evidence that C/L-gelsolin participates in the bone morphogenetic protein (BMP)/Smad dorsal-ventral signaling pathway is reviewed. Finally, we speculate that soluble C/L-gelsolin:actin complexes in the cornea may be analogous to soluble alphaA:alphaB-crystallin complexes in the lens. Together, our data are consistent with an analogy between the abundance of gelsolin in fish corneas and taxon-specific multifunctional crystallins in lenses.
Kanungo
Jyotshnabala
J
Laboratory of Molecular and Developmental Biology, National Eye Institute, National Institutes of Health, 7 Memorial Drive, Building. 7, Room 100A, Bethesda, MD 20892, USA.
Swamynathan
Shivalingappa K
SK
Piatigorsky
Joram
J
D000818:Animals; D003315:Cornea / Q000033:anatomy & histology / Q000378:metabolism*; D003459:Crystallins / Q000235:genetics / Q000378:metabolism*; D005399:Fishes / Q000033:anatomy & histology / Q000378:metabolism*; D018260:Gelsolin / Q000378:metabolism*; D015870:Gene Expression; D017403:In Situ Hybridization; D007908:Lens, Crystalline / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015027:Zebrafish / Q000033:anatomy & histology / Q000378:metabolism
D003459:Crystallins; D018260:Gelsolin; D012333:RNA, Messenger