Misexpression of Xsiah-2 induces a small eye phenotype in Xenopus

Recent data demonstrate a structural and functional conservation of factors crucial for the development of the insect and the vertebrate eye. We isola ted Xenopus siah-2, a protein with 67% identity to Drosophila sina (seven i n absentia) and 85% identity to the mouse and human siah-2 proteins. Sina i s required in Drosophila for the R7 photoreceptor cell formation during eye development, because it down regulates proteins that inhibit R7 differenti ation via the ubiquitin/proteasome pathway. Nothing is known about the deve lopmental function of the siah protein in vertebrates. We show that in Xeno pus siah-2 is expressed maternally and is later restricted to the brain, sp inal cord and the developing and mature eye. To demonstrate that the verteb rate factor participates in the process of eye formation we over expressed Xsiah-2 during Xenopus development and observed the formation of a small ey e phenotype. The vertebrate counterpart of a C-terminal loss of Function si na mutant, that causes a deficiency of the R7 photoreceptor cells in Drosop hila, induces in Xenopus also smaller eyes. The small eyes are characterize d by a reduced size of the lens, the retina and the pigmented epithelium. A s this phenotype has been also described for flies expressing sina ectopica lly, the data demonstrate the functional and structural conservation of Xsi ah-2 and sina in metazoan eye development. (C) 2001 Elsevier Science Irelan d Ltd. All rights reserved.