Interaction of mouse polycomb-group (Pc-G) proteins Enx1 and Enx2 with Eed: Indication for separate Pc-G complexes

The Polycomb group (Pc-G) constitutes an important, functionally conserved group of proteins, required to stably maintain inactive homeobox genes repressed during development. Drosophila extra sex combs (esc) and its mammalian homolog embryonic ectoderm development (eed) are special Pc-G members, in that they are required early during development when Pc-G repression is initiated, a process that is still poorly understood. To get insight in the molecular function of fed, we searched for fed-interacting proteins, using the yeast two-hybrid method. Here we describe the specific in vivo binding of fed to Enx1 and End, two mammalian homologs of the essential Drosophila Pc-G gene Enhancer-of-zeste [E(z)]. No direct biochemical interactions were found between Fed/Enx and a previously characterized mouse Pc-G protein complex, containing several mouse Pc-G proteins including mouse polyhomeotic (Mph1). This suggests that different Pc-G complexes,vith distinct functions may exist. However, partial colocalization of Enx1 and Mph1 to subnuclear domains may point to more transient interactions between these complexes, in support of a bridging role for Enx1.