Chk2 and P53 Regulate the Transmission of Healed Chromosomes in the Drosophila Male Germline

Simon W A Titen,Jayaram Bhandari,Ho-Chen Lin,Kent G Golic,Jeff Sekelsky

doi:10.1371/journal.pgen.1004130

Abstract

When a dicentric chromosome breaks in mitosis, the broken ends cannot be repaired by normal mechanisms that join two broken ends since each end is in a separate daughter cell. However, in the male germline of Drosophila melanogaster, a broken end may be healed by de novo telomere addition. We find that Chk2 (encoded by lok) and P53, major mediators of the DNA damage response, have strong and opposite influences on the transmission of broken-and-healed chromosomes: lok mutants exhibit a large increase in the recovery of healed chromosomes relative to wildtype control males, but p53 mutants show a strong reduction. This contrasts with the soma, where mutations in lok and p53 have the nearly identical effect of allowing survival and proliferation of cells with irreparable DNA damage. Examination of testes revealed a transient depletion of germline cells after dicentric chromosome induction in the wildtype controls, and further showed that P53 is required for the germline to recover. Although lok mutant males transmit healed chromosomes at a high rate, broken chromosome ends can also persist through spermatogonial divisions without healing in lok mutants, giving rise to frequent dicentric bridges in Meiosis II. Cytological and genetic analyses show that spermatid nuclei derived from such meiotic divisions are eliminated during spermiogenesis, resulting in strong meiotic drive. We conclude that the primary responsibility for maintaining genome integrity in the male germline lies with Chk2, and that P53 is required to reconstitute the germline when cells are eliminated owing to unrepaired DNA damage.

Highlights

Barbara McClintock discovered that dicentric chromosomes produced in germ cells of corn plants could break, and that the broken chromosomes could be transmitted and have a new telomere added to the broken end
In somatic cells the tumor suppressors Chk2 and P53 can induce suicide of cells with such a chromosome and eliminate the danger. Though, such chromosomes can be healed by the addition of a new telomere cap, and may be transmitted to the generation
We find that Chk2 and P53 regulate healing in the germline, but in seemingly opposite directions

Summary

Introduction

Barbara McClintock discovered that dicentric chromosomes produced in germ cells of corn plants could break, and that the broken chromosomes could be transmitted and have a new telomere added to the broken end. She called this process healing [1,2]. Dicentric chromosomes can be efficiently produced in Drosophila melanogaster by FLP-mediated recombination between FRTs in opposite orientation on sister chromatids (Figure 1A) [11] Such chromosomes typically break in the subsequent mitotic division, delivering a chromosome with a single broken end to each daughter cell [12]. The use of a Y chromosome avoids complications owing to aneuploidy that might result if dicentrics were produced on the X or an autosome [12]

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