Lukacs, A. | bioRxiv Science

bioRxiv2018

Intricate structure of the interphase chromocenter revealed by the analysis of a factor involved in species formation

In higher eukaryotes centromeres often coalesce into a large intranuclear domain called the chromocenter. Chromocenters are important for the organization of pericentric heterochromatin and a disturbance of their formation results in an upregulation of repetitive elements and causes defects in chromosome segregation. Mutations in the gene encoding for the centromere associated Drosophila speciation factor HMR show very similar phenotypes suggesting a role of HMR in chromocenter architecture and function. We performed confocal and super resolution microscopy as well as proximity based biotinylation experiments of HMR and its associated protein HP1a to generate a molecular map of HMR and HP1a bound chromatin. Our work reveals an intricate internal structure of the centromeric chromatin region, which suggests a role of HMR in separating heterochromatin from centromeric chromatin.

biochemistry↗

bioRxiv2018

Altered chromatin localization of hybrid lethality proteins in Drosophila

Understanding hybrid incompatibilities is a fundamental pursuit in evolutionary genetics. In crosses between Drosophila melanogaster females and Drosophila simulans males, the interaction of at least three genes is necessary for hybrid male lethality: Hmr mel, Lhr sim, and gfzf sim. All three hybrid incompatibility genes are chromatin associated factors. While HMR and LHR physically bind each other and function together in a single complex, the connection between either of these proteins and gfzf remains mysterious. Here, we investigate the allele specific chromatin binding patterns of gfzf. First, our cytological analyses show that there is little difference in protein localization of GFZF between the two species except at telomeric sequences. In particular, GFZF binds the telomeric retrotransposon repeat arrays, and the differential binding of GFZF at telomeres reflects the rapid changes in sequence composition at telomeres between D. melanogaster and D. simulans. Second, we investigate the patterns of GFZF and HMR co-localization and find that the two proteins do not normally co-localize in D. melanogaster. However, in inter-species hybrids, HMR shows extensive mis-localization to GFZF sites, and this altered localization requires the presence of gfzf sim. Third, we find by ChIP-Seq that over-expression of HMR and LHR within species is sufficient to cause HMR to mis-localize to GFZF binding sites, indicating that HMR has a natural low affinity for GFZF sites. Together, these studies provide the first insights into the different properties of gfzf between D. melanogaster and D. simulans as well as a molecular interaction between gfzf and Hmr in the form of altered protein localization.

molecular biology↗