The nuclear distribution of Polycomb during Drosophila melanogaster development shown with a GFP fusion protein

The chromatin protein Polycomb (PC) is necessary for keeping homeotic genes repressed in a permanent and heritable manner. PC is part of a large multi meric complex (PcG proteins) involved in generating silenced chromatin doma ins at target genes, thus preventing their inappropriate expression. In ord er to assess the intranuclear distribution of PC during mitosis in differen t developmental stages as well as in the germ line we generated transgenic fly lines expressing a PC-GFP (Green Fluorescent Protein) fusion protein. R apidly dividing nuclei were found to display a rather homogeneous PC-GFP di stribution. However, with increasing differentiation a pronounced subnuclea r pattern was observed. In all investigated diploid somatic tissues the bul k of PC-GFP fusion protein is depleted from the chromosomes during mitosis: however, a detectable fraction remains associated. In the male germ line i n early spermatogenesis, PC-GFP was closely associated with the chromosomal bivalents and gradually lost at later stages. Interestingly, we found that PC is associated with the nucleolus in spermatocytes, unlike somatic nucle i. In contrast to mature sperm showing no PC-GFP signal the female germ lin e retains PC in the germinal vesicle.