Homolog-Dependent Repair Following Dicentric Chromosome Breakage in Drosophila melanogaster

Abstract

Double-strand DNA breaks are repaired by one of several mechanisms that rejoin two broken ends. However, cells are challenged when asked to repair a single broken end and respond by: (1) inducing programmed cell death; (2) healing the broken end by constructing a new telomere; (3) adapting to the broken end and resuming the mitotic cycle without repair; and (4) using information from the sister chromatid or homologous chromosome to restore a normal chromosome terminus. During one form of homolog-dependent repair in yeast, termed break-induced replication (BIR), a template chromosome can be copied for hundreds of kilobases. BIR efficiency depends on Pif1 helicase and Pol32, a nonessential subunit of DNA polymerase δ. To date, there is little evidence that BIR can be used for extensive chromosome repair in higher eukaryotes. We report that a dicentric chromosome broken in mitosis in the male germline of Drosophila melanogaster is usually repaired by healing, but can also be repaired in a homolog-dependent fashion, restoring at least 1.3 Mb of terminal sequence information. This mode of repair is significantly reduced in pif1 and pol32 mutants. Formally, the repaired chromosomes are recombinants. However, the absence of reciprocal recombinants and the dependence on Pif1 and Pol32 strongly support the hypothesis that BIR is the mechanism for restoration of the chromosome terminus. In contrast to yeast, pif1 mutants in Drosophila exhibit a reduced rate of chromosome healing, likely owing to fundamental differences in telomeres between these organisms.

Silence at the End: How Drosophila Regulates Expression and Transposition of Telomeric Retroelements

“…In some instances, as for Drosophila biarmipes and possibly also for Drosophila takahashii, telomere retroelements became inactive and recombination-based mechanisms emerged as the principal mean to regulate J o u r n a l P r e -p r o o f telomere length [17]. Furthermore, in Drosophila melanogaster retrotransposition of active telomeric elements coexists with gene conversion and very likely with BIR-mediated healing [90,143,152].…”

The DNA polymerases of Drosophila melanogaster

“…However, genetic approaches have been used to show that PolD3 is essential for DNA replication in early embryogenesis [ 58 , 63 ]. Interestingly, PolD3 is also required for the repair of double-strand breaks by homologous recombination involving extensive DNA synthesis [ 59 ] and for break-induced replication during repair of single broken strands [ 64 ], though it’s unclear whether PolD functions within the polymerase delta or zeta complex in these roles (see below). Genetic interactions between PolD3 and the other two delta subunits have been reported, supporting functional associations in vivo [ 58 ].…”

The Cyclically Seasonal Drosophila subobscura Inversion O7 Originated From Fragile Genomic Sites and Relocated Immunity and Metabolic Genes

“…It is known that this type of events can trigger BIR and MMBIR repair (Sakofsky et al, 2015). Of the two pathways, the second pathway has yet to be identified in Drosophila (Alexander et al, 2016;Bhandari et al, 2019). A possible scenario is detailed in Figure 10: first, non-B DNA-induced stalling of a replication fork at the proximal breakpoint of a ch-cu-type chromosome led to two DSBs generating three fragments.…”