Functional analysis of the eye genetic network in planarian regeneration

Abstract

Metazoan eyes are specified by the concerted action of several conserved nuclear factors that act co-ordinately in agenetic network. Pax6, a member of the paired-box family and sine oculis, a homeobox containing gene, are some of the players in that conservative genetic cascade that we have characterized in Platyhelminthes. Freshwater planarians detect light intensity through their eyespots. Although being very simple, they contain two cell types: photoreceptor and pigment cells, The photoreceptor cells are bipolar nerve cells that connect directly to the cephalic ganglia. They also differentiate into a microvilli extent from the dendrite, the rhabdomer, where the opsin photopigment accumulates. The pigmented cells aggregate to form a cup shape in the dorsal head region. In our search for the planarian eye genetic network we have characterized two Pax6 genes and two sine oculis genes. Functional analysis by loss of function using RNA interference (RNAi) approaches shows that the two Pax6 genes are partially dispensable, while the sine oculis gene homologous to the Six-1 family is essential for eye formation during head regeneration and for functional eye maintenance in adult planarians.