Sfrp1 demarcates the anterior neural plate and promotes eye development in the chick embryo

Secreted frizzled related proteins (SFRPs) are a new class of signaling molecules that antagonize the activity of Wnt proteins. However, the full range of SFRP activities and mechanisms of action are not fully understood. In our search for molecules which may participate in the development of the eye, we have isolated the chick homologue of Sfrp1. Here we show that in chick, Sfrp1 has a widespread and dynamic expression in the most anterior portion of the embryo. At later stages of development, Sfrp1 continues to be expressed with a pattern that is consistent with a function in cell fate determination and differentiation in both the eye and the neural tube. On the basis of this expression pattern, we have analyzed possible roles of Sfrp1 in the development of chick embryos. With in vitro and in vivo experiments, we show here that Sfrp1 has a dual function in the development of the chick retina: it promotes axon outgrowth and increases neuronal differentiation, while inhibiting cell proliferation.