Interaction of Mouse Polycomb-Group (Pc-G) Proteins Enx1 and Enx2 with Eed: Indication for Separate Pc-G Complexes

ABSTRACT

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 Eed, we searched for Eed-interacting proteins, using the yeast two-hybrid method. Here we describe the specific in vivo binding of Eed to Enx1 and Enx2, two mammalian homologs of the essential DrosophilaPc-G gene Enhancer-of-zeste[E(z)]. No direct biochemical interactions were found between Eed/Enx and a previously characterized mouse Pc-G protein complex, containing several mouse Pc-G proteins includingmouse polyhomeotic (Mph1). This suggests that different Pc-G complexes with 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.

ACKNOWLEDGMENTS

We thank O. Hobert and A. Ullrich for generously sharing the Enx1 antiserum and the ΔENX1 two-hybrid construct, T. Jenuwein for providing the epitope-tagged ENX1/EZH2 cDNA constructs, and J. Jacobs for developing the RT-PCR protocol.

This work was supported in part by the Life Sciences Foundation (SLW) grant, which is subsidized by the Netherlands Organization for Scientific Research (NWO), to J.W.V., and by an NIH grant (HD24462) to T.M.