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H. Mu, K. Ohta, S. Kuriyama, H. Tanihara, H. Tanaka; Molecular Cloning and Characterization of Equarin, a Novel Soluble Molecule Expressed With Polarity at Chick Embryonic Lens Equator . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1090.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The development of the eye is controlled by a combination of intrinsic and extrinsic signals. For example, the lens has been shown to be an important source of signals for the development of the eye. Our study was conducted in an attempt to identify secreted molecule(s) that mediate the signals expressed in the lens. Methods: A chick E6 lens cDNA library was used for the identification of soluble molecules that are secreted from the lens using signal sequence trap (SST). In an attempt to reveal temporal and special expression pattern of the identified molecule, in situ hybridization was conducted. Also, translated proteins were subjected to immunoblotting and immunocytochemistry. Function of the identified molecules on eye development was analyzed by microinjection mRNA into Xenopus embryos. Results: From a total of 2 x 106clones, 177 plasmid DNAs were recovered, and cDNA inserts were sequenced. Of these, five clones were identified as unknown molecules encoding genuine signal sequences. In situ hybridization demonstrated that, one (clone #15) of the five novel molecules, was preferentially expressed in the equatorial region of the lens, and we designated this molecule as "equarin." Cloning of full length cDNA and deduced amino acid sequence of equarin revealed that there are two alternative splicing forms, and that they encode consensus repeat domains conserved in human SRPX (a retinitis pigmantosa-associated gene). During chick embryonic eye development, equarin mRNA is expressed exclusively in the lens from early stages and later persists in the lens equatorial region in a high-dorsal-to-low-ventral gradient till postnatal day 2. In vitro analysis of equarin protein indicated that after translation, it is modified, cleaved and secreted to extracellular matrix. Microinjection of equarin mRNA into Xenopus embryos induced abnormal ventral eye formation. Conclusions: Our results suggest that equarin is one of the candidates for the signaling molecules from the lens that are involved in eye morphogenesis.
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