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T. Dadon–Dahan, M. Spencer, E. Nevo, J. Piatigorsky; Differential Expression of B1 and B2 Crystallin in Zebrafish . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3133.
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There are two zebrafish αB–crystallin genes (αB1 and αB2) with 53% amino acid sequence identity. In adults, αB1–crystallin expression is restricted mainly to the lens, while αB2–crystallin expression includes lens, heart, brain, muscle and liver. We are interested in the molecular basis for the differential regulation of the two αB–crystallin genes. As an initial step, we explore here their developmental expression pattern.
αB1 and αB2–crystallin gene expression was examined at 24 and 48 hours post fertilization (hpf; embryonic) by whole–mount in situ hybridization (wm–ISH) and at 3 to 20 days post fertilization (dpf; larval) and in adults by RT–PCR. αB1–crystallin cDNA was cloned into TOPO–4 vector; αB2–crystallin cDNA clone was purchased from ATCC (in pExpress1 vector). Digoxigenin –UTP labeled RNA probes were generated from the cDNA clones by in vitro transcription and used for wm–ISH. EMBOSS–Align pairwise sequence local alignment was used to compare the αB1 and αB2–crystallin 5’–flanking regions.
αB1–crystallin is expressed in the 4th ventricle of the brain at 24 hpf and also in the heart and possibly optic tectum at 48 hpf. αB1–crystallin expression was not detected in the lens before 13dpf; it was high in lens and lower in brain in adults (other tissues were not examined). αB2–crystallin was detected in most of the embryonic tissues including lens at 24 and 48 hpf, and in the lens and tail of larvae. In adults, αB2–crystallin expression was confirmed in lens and brain. Other larval and adult tissues have not been examined yet. 5’–flanking sequences (640 bp) of the αB1 and αB2–crystallin genes showed 43% identity to each other and 45% and 41% identity to the 640 bp mouse αB–crystallin promoter/enhancer, respectively.
αB1 and αB2–crystallin gene expression patterns include significant temporal and quantitative as well as tissue–specific differences in zebrafish. In contrast to the lens–preferred expression of αB1–crystallin in adults, only the αB2–crystallin gene is expressed in the lens during embryogenesis. The two zebrafish αB–crystallin genes provide a useful model for the evolution of regulation of duplicated genes.
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