Biology subjects

Rafanel, B.

Publications and source records attributed to Rafanel, B..

3 recordsLinked to original sources

bioRxiv2025

Antisense transposon insertions into host genes trigger piRNA mediated immunity

Transposable elements pose a persistent threat to genome integrity, yet how host defense systems adapt to newly invading elements remains poorly understood. Here, we reveal how Drosophila melanogaster acquired PIWI-interacting RNA (piRNA)-mediated immunity against the recently invading endogenous retrovirus tirant. By integrating genetics, small RNA profiling, and population genomics, we identify two distinct modes of de novo piRNA biogenesis. The primary mechanism involves antisense insertions into the flamenco cluster, a well-established master locus for transposon control. Strikingly, we also find that antisense tirant insertions into 3' UTRs of host genes robustly trigger piRNA production, a process driven by host gene transcription but independent of gene identity. These findings challenge prevailing models that link piRNA precursor specification to genomic origin or nuclear processing context. Instead, they uncover a flexible, general mechanism in which transposition into host gene exons represents a critical vulnerability for transposons: by generating chimeric antisense transcripts that are exported to the cytoplasm, transposons inadvertently initiate their own silencing, enabling rapid and adaptive genome defense against new invaders.

genetics↗

bioRxiv2025

Direct cell-to-cell transmission of retrotransposons

Transposable elements are abundant in host genomes but are generally considered to be confined to the cell in which they are expressed, with the notable exception of endogenous retroviruses. Here, we identify a group of LTR retrotransposons that infect the germline from somatic cells within the Drosophila ovary, despite lacking the fusogenic Envelope protein typically required for retroviral entry. Instead, these elements encode a short transmembrane protein, sORF2, with structural features reminiscent of viral cell-cell fusogens. Through genetics, imaging, and electron microscopy, we show that sORF2 localizes to invasive somatic protrusions, enabling the direct transfer of retrotransposon capsids into the oocyte. Remarkably, sORF2-like proteins are widespread among insect retrotransposons and also occur in piscine nackednaviruses and avian picornaviruses. These findings reveal a noncanonical, Envelope-independent transmission mechanism shared by retrotransposons and non-enveloped viruses, offering important insights into host-pathogen evolution and soma-germline interactions.

genetics↗

bioRxiv2023

Functional Adaptations of Endogenous Retroviruses to the Drosophila Host Underlie their Evolutionary Diversification

Transposable elements profoundly affect the biology and evolution of their hosts, yet their own evolutionary dynamics remain poorly understood. Here, we investigate insect endogenous retroviruses (iERVs), a monophyletic group of LTR retrotransposons that have acquired the trait of infectivity, likely through capture of a Baculovirus envelope gene. In Drosophila ovaries, iERVs with functional envelope have adapted their cis-regulatory sequences to be expressed in any somatic cell type, from where they infect the germline. Strikingly, related retroviruses show distinct expression patterns, indicating niche partitioning. In contrast, all non-infectious iERVs that emerged through secondary envelope-loss are specifically expressed in the germline. Co-evolving with iERVs, the genome-protecting piRNA pathway has assimilated iERV promoter and sequence information into piRNA clusters, underscoring the functional significance of iERV expression in somatic niches. We propose that the evolutionary innovation of cell-to-cell infectivity has triggered the adaptive radiation of iERVs through trait diversification and antagonistic virus-host interactions, processes that likely underpin niche-specific expression of endogenous retroviruses in vertebrates as well.

evolutionary biology↗