Drosophila IRBP bZIP heterodimer binds P-element DNA and affects hybrid dysgenesis

Abstract

In Drosophila, P-element transposition causes mutagenesis and genome instability during hybrid dysgenesis. The P-element 31-bp terminal inverted repeats (TIRs) contain sequences essential for transposase cleavage and have been implicated in DNA repair via protein-DNA interactions with cellular proteins. The identity and function of these cellular proteins were unknown. Biochemical characterization of proteins that bind the TIRs identified a heterodimeric basic leucine zipper (bZIP) complex between an uncharacterized protein that we termed "Inverted Repeat Binding Protein (IRBP) 18" and its partner Xrp1. The reconstituted IRBP18/Xrp1 heterodimer binds sequence-specifically to its dsDNA-binding site within the P-element TIRs. Genetic analyses implicate both proteins as critical for repair of DNA breaks following transposase cleavage in vivo. These results identify a cellular protein complex that binds an active mobile element and plays a more general role in maintaining genome stability.T ransposable elements contribute significantly to the organization and evolution of all eukaryotic genomes. Recent estimates of transposon content within the Drosophila melanogaster genome are between 5% and 10%, and in humans over half the genome is composed of mobile elements (1, 2). Although many of these elements, including the Drosophila P-element transposon, are still active (3), the cellular mechanisms used to combat the genotoxic effects of DNA double-strand breaks (DSBs) generated by transpositional recombination are not fully understood. The Drosophila P-transposable element provides an excellent model for understanding the ancient mechanisms used by the cell to counteract newly invading parasitic mobile DNA elements (4).The P-element transposon is a mobile DNA element that spread through wild populations of D. melangaster ∼100 y ago after most common laboratory strains were isolated (5, 6). P elements were identified by studying a genetic syndrome called "P-M hybrid dysgenesis." It was observed that males from wild populations (P strains) crossed to females from isolated laboratory stocks (M strains) yielded progeny that had germline mutations, temperature-sensitive sterility, and atypical male recombination (6). Reciprocal crosses yielded phenotypically normal progeny. The P element was shown to be the causative agent of these so-called P-M hybrid dysgenesis phenotypes by molecular analyses showing that P elements were present in variable locations in P strains yet totally absent from most M strains (7,8).The Drosophila P-element transposon encodes a GTP-dependent site-specific DNA transposase/integrase family enzyme (9, 10). At each end of the P-element transposon are perfect 31-bp terminal inverted repeats (TIRs), 11-bp internal inverted repeats that serve as enhancers of transposition, and internal 10-bp transposase binding sites (11-13) (Fig. 1A). The P-element transposase catalyzes DNA cleavage within the 31-bp TIRs to create 17-nt 3′ single-strand extensions at both the donor site and the transposon ends (14, 15)...

Inter-Organ Growth Coordination Is Mediated by the Xrp1-Dilp8 Axis in Drosophila

“…Xrp1 was previously involved in genotoxic stress (irradiation) response, and the maintenance of genome integrity downstream of p53 (Akdemir et al, 2007) and during P-element dysgenesis (Francis et al, 2016). Our results uncover another function for Xrp1 as a growth regulator.…”

“…Xrp1 has previously been implicated in the response to genotoxic stress (irradiation), the maintenance of genome integrity downstream of p53 (Akdemir et al, 2007) and during P-element dysgenesis (Francis et al, 2016). In order to gain insights into its putative growth-related function, we generated transgenic animals expressing the short and the long isoforms of Xrp1 under UAS control (UAS-xrp1-S and UAS-xrp1-L).…”

Inter-organ growth coordination is mediated by the Xrp1/Dilp8 axis in Drosophila

“…Xrp1 was previously involved in genotoxic stress (irradiation) response, and the maintenance of genome integrity downstream of p53 (Akdemir et al, 2007) and during P-element dysgenesis (Francis et al, 2016). Our results uncover a new function for Xrp1 as a growth regulator.…”

Mechanisms underlying the cooperation between loss of epithelial polarity and Notch signaling during neoplastic growth in Drosophila

“…5D,E,K) whereas the knock-down of Xrp1 very efficiently suppressed the growth and Mmp1 expression in NS tissues. This suggests that .CG6272/CEBPG could be acting in combination with its bZIP partner Xrp1 in this context (Francis et al, 2016; Reinke et al, 2013). Although the cellular processes controlled by CG6272/Xrp1 remain to be determined, the fact that Xrp1 is an early p53 target gene (Akdemir et al, 2007; Link et al, 2013), raises the possibility that its functions could be related to DNA/genome integrity maintenance.…”

“…Interestingly, we did not observe any effect knocking down Crc , the fly Atf4 homologue, suggesting that during NS overgrowth in Drosophila , CG6272/Irbp18 could be acting in combination with another partner. CG6272/Irbp18 also interacts with Xrp1, and the heterodimer has been implicated in DNA repair (Akdemir et al, 2007; Francis et al, 2016). We thus propose that the Irbp18/Xrp1 dimer is activated in NS and is required to facilitate DNA repair and ensure genomic stability to prevent catastrophic genotoxic effect upon the combined cellular stresses of S and replication stress of N. Recently, Xrp1 together with its binding partner CG6272/Irbp18 (but not Atf4) has been shown to mediate a loser status in ribosomal genes deficient cells, through the implementation of a specific transcriptional program (Baillon et al, 2018; Blanco et al, 2020; Ji et al, 2019).…”