EXPRESSION OF DJY1, A PROTEIN CONTAINING A COLD SHOCK DOMAIN AND RG REPEAT MOTIFS, IS TARGETED TO SITES OF REGENERATION IN PLANARIANS

Planarians are well-known for their exceptional regenerative abilities . This investigation focuses on the involvement of a Y-box protein, de fined by the presence of a cold-shock domain, in regeneration-specific processes. Previous studies have shown that developmentally expressed Y-box proteins bind to mRNA molecules and regulate the timing of thei r translation. We have isolated and characterized a planarian Y-box ge ne, DjY1, which is specifically expressed at the site of regeneration, the blastema. DjY1 transcripts appear rapidly at the site of cutting and increase in number as the blastema grows. The timing and level of expression is similar irrespective of the orientation of the cut: in a nterior, posterior, and lateral regenerative tissue. As regeneration n ears completion, there is a general decrease in transcript level excep t in structures which are still differentiating, specifically in the a uricles where new DjY1 transcripts are produced, A similarly modulated temporal pattern of expression throughout regeneration is seen in ass aying the DjY1 protein. Within the population of blastemal cells, a su bset of differentiating cells is specifically immunostained using anti bodies to DjY1. The DjY1 protein contains a cold-shock domain and RG-r epeat motifs, both of which are associated with RNA-binding properties : in vitro binding studies using recombinant DjY1 show that the prefer red template is single-stranded RNA of heterogeneous sequence. These d ata provide the first direct evidence that a Y-box protein is involved in the regeneration process in planarians and implicate DjY1 in the t ranslational regulation of: differentiation-specific mRNAs. (C) 1998 A cademic Press.