The Integrity of the HMR complex is necessary for centromeric binding and reproductive isolation in Drosophila

Abstract

Postzygotic isolation by genomic conflict is a major cause for the formation of species. Despite its importance, the molecular mechanisms that result in the lethality of interspecies hybrids are still largely unclear. The genus Drosophila, which contains over 1600 different species, is one of the best characterized model systems to study these questions. We showed in the past that the expression levels of the two hybrid incompatibility factors Hmr and Lhr diverged in the two closely related Drosophila species, D. melanogaster and D. simulans, resulting in an increased level of both proteins in interspecies hybrids. The overexpression of the two proteins also leads to mitotic defects, a misregulation in the expression of transposable elements and decreased fertility in pure species. In this work, we describe a distinct six subunit protein complex containing HMR and LHR and analyse the effect of Hmr mutations on complex integrity and function. Our experiments suggest that HMR needs to bring together components of centromeric and pericentromeric chromatin to fulfil its physiological function and to cause hybrid male lethality.

The role of RNA in the maintenance of chromatin domains as revealed by antibody-mediated proximity labelling coupled to mass spectrometry

“…R-loop-ChIP experiments were performed on cells expressing the either ‘EGFP-2xHBD-3xFLAG’ or HBD mutant ‘EGFP-2xHBD(WKK)-3xFLAG’ protein by using standard ChIP protocol as in Lukacs et al, 2021 with modifications. Briefly, 5–7 × 10 7 cells after RNAi treatment were harvested and crosslinked with 1% FA for 10 min in RT.…”

Molecular conflicts disrupting centromere assembly contribute to Xenopus hybrid inviability

“…For example, disruption of the chromocenter, a domain containing the pericentromeric satellite DNA, is common among Drosophila hybrids and may underlie inviability (Jagannathan and Yamashita, 2021). Furthermore, known inviability factors such as hybrid male rescue (Hmr) and lethal hybrid rescue (Lhr) strongly impact chromosome segregation in Drosophila hybrids and have been reported to regulate transposable elements and heterochromatic repeats (Thomae et al, 2013; Satyaki et al, 2014), associate with chromatin chaperones adjacent to centromeres (Anselm et al, 2018), and to link pericentromeric and centromeric chromatin to maintain centromere integrity (Lukacs et al, 2021). However, whether these factors play a direct role in centromere function is unclear (Blum et al, 2017).…”

Molecular conflicts disrupting centromere maintenance contribute to Xenopus hybrid inviability

“…17 Furthermore, known inviability factors such as hybrid male rescue (Hmr) and lethal hybrid rescue (Lhr) strongly impact chromosome segregation in Drosophila hybrids and have been reported to regulate transposable elements and heterochromatic repeats, 18,19 associate with chromatin chaperones adjacent to centromeres, 20 and to link pericentromeric and centromeric chromatin to maintain centromere integrity. 21 However, whether these factors play a direct role in centromere function is unclear. 22 Despite these advances, the relative contribution to hybrid inviability of diverging centromere sequences versus the activity and spatial organization of associated chromatin machineries that promote centromere assembly and maintenance is poorly understood.…”