Equarin, a novel soluble molecule expressed with polarity at chick embryonic lens equator, is involved in eye formation

The lens plays an important role in eye development. To investigate the molecular mechanisms involved, we used signal sequence trap screens with a chicken lens cDNA library and identified a novel secreted molecule, equarin. Equarin encodes consensus repeat domains conserved in human SRPX and mouse Urb. In the embryonic eye, equarin transcript is detected exclusively in the lens, and persists in the lens equatorial region in a high-dorsal-to-low-ventral gradient. In vitro analysis of equarin protein indicated that after translation, it is modified, cleaved, and secreted to extracellular locations. Microinjection of equarin mRNA into Xenopus embryos induced abnormal eye development. These data suggest that equarin is involved in eye formation.