Chromatin organisation of transgenes in Dictyostelium

The introduction of transgenes in Dictyostelium discoideum typically results in the integration of the transformation vector into the genome at one or a few insertion sites as tandem arrays of approximately 100 copies. Exceptions are extrachromosomal vectors, which do not integrate into chromosomes, and vectors containing resistance markers such as blasticidin, which integrate as single copies at one or a few sites. Here we report that low copy number vector inserts display typical euchromatic features while high copy number insertions are enriched for modifications associate with heterochromatin. Interestingly, high copy number insertions also colocalise with heterochromatin, are enriched for the centromeric histone CenH3 and display centromere-like behaviour during mitosis. We also found that the chromatin organisation on extrachromosmal transgenes is different from those integrated into the chromosomes.