Biology subjects

Tracy, L.

Publications and source records attributed to Tracy, L..

5 recordsLinked to original sources

bioRxiv2025

Safeguarding spermatogenesis from retrotransposon insertions by forming ecDNA

Retrotransposon mobilization in germline cells enables the rewriting of genetic information to drive genome innovation, species evolution, and adaptation through the generation of de novo mutations. However, uncontrolled mobilization can cause DNA breaks and genome instability, often leading to sterility. How germ cells balance retrotransposon-induced genome innovation with the need for genomic integrity remains poorly understood. Here, we used Drosophila spermatogenesis as a model to investigate retrotransposon mobilization dynamics. Although many retrotransposon families are transcriptionally active, we found that the LTR-retrotransposon nomad completes the full mobilization cascade--including mRNA export, protein translation, and reverse transcription--to produce double-stranded DNA (dsDNA) the most efficiently. Strikingly, despite successfully generating dsDNA, nomad rarely achieves genomic reintegration. Instead, its newly synthesized DNA predominantly forms extrachromosomal circular DNA (ecDNA). These findings suggest that ecDNA formation acts as a protective mechanism to sequester retrotransposon-derived DNA and prevent widespread genomic integration during spermatogenesis, thereby preserving genome stability while allowing limited retrotransposon activity.

genomics↗

bioRxiv2022

Retrotransposons hijack alt-EJ DNA repair process for mobilization and eccDNA biogenesis

Parasitic retrotransposons populate in the genome to rewrite the hosts genetic code. How retrotransposons use the host factors to achieve their propagation remains largely unclear. Here we report retrotransposons hijack the alternative end-joining (alt-EJ) DNA repair process to accomplish mobilization cycle. We applied Nanopore sequencing to examine the fates of replicated retrotransposon DNA, and found that only 10% of them achieve integration, while 90% exist as extrachromosomal circular DNA (eccDNA). Using eccDNA production as a readout, further genetic screens identified factors from alt-EJ as essential for retrotransposon replication. alt-EJ drives the 2nd-strand synthesis of the retrotransposon DNA via a circularization process, thus is necessitated for eccDNA production and integrations. Our study reveals a conserved function of alt-EJ in promoting selfish element propagation, which potentially causes disease or drives evolution.

cell biology↗

bioRxiv2021

Lack of blocking activity in anti-CTLA-4 antibodies reduces toxicity, but not anti-tumor efficacy

Anti-CTLA-4 antibodies such as ipilimumab were among the first immune-oncology agents to show significantly improved outcomes for patients. However, existing anti-CTLA-4 therapies fail to induce a response in a majority of patients and can induce severe, immune-related adverse events. It has been assumed that checkpoint inhibition, i.e., blocking the interaction between CTLA-4 and its ligands, is the primary mechanism of action for ipilimumab. In this study we present evidence that checkpoint inhibition is not a primary mechanism of action for efficacy of anti-CTLA-4 antibodies. Instead, the primary mechanism for efficacy is FcR-mediated Treg depletion in the tumor microenvironment. First, we identified a monoclonal antibody (mAb) that binds to CTLA-4 at an epitope that differs from ipilimumabs by only a few amino acids, yet has limited checkpoint inhibitor activity. Surprisingly, the weak checkpoint inhibitor has superior anti-tumor activity compared to ipilimumab in a murine model. The weak checkpoint inhibitor also induces less Treg proliferation and has increased ability to induce in vitro FcR signaling and in vivo depletion of intratumoral Tregs. Further experiments showed that the enhanced FcR activity of the weak checkpoint inhibitor likely contributes to its enhanced anti-tumor activity. Importantly, we also showed that weak checkpoint inhibition was associated with lower toxicity in murine models. Our work suggests that new anti-CTLA-4 drugs should be optimized for Treg depletion rather than checkpoint inhibition.

immunology↗

bioRxiv2020

Developmental retrotransposon activation primes host immunity for future viral-clearance

Transposons are thought to be largely suppressed under physiological conditions, ensuring that their mobilization is a rare event. By tracking mobilization, we show that during metamorphosis at the Drosophila pupal stage, the Gypsy retrotransposon selectively mobilizes in regenerating tissues. In the newly formed tissues, this wave of Gypsy activation primes the hosts innate immune system by inducing the production of antimicrobial peptides (AMPs). Moreover, early immune-priming functions of Gypsy are essential for combating viral invasion in adult flies: flies with Gypsy being silenced at the pupal stage are unable to clear viruses and succumb to viral infection. Our data reveal that regulated activation of transposons during animal developmental endows a long-term benefit in pathogen warfare.

developmental biology↗

bioRxiv2020

Capturing and Recreating Diverse Antibody Repertoires as Multivalent Recombinant Polyclonal Antibody Drugs

Plasma-derived polyclonal antibodies are polyvalent drugs used for many important clinical indications that require modulation of multiple drug targets simultaneously, including emerging infectious disease and transplantation. However, plasma-derived drugs suffer many problems, including low potency, impurities, constraints on supply, and batch-to-batch variation. In this study, we demonstrated proofs-of-concept for a technology that uses microfluidics and molecular genomics to capture diverse mammalian antibody repertoires as multivalent recombinant drugs. These "recombinant hyperimmune" drugs comprised thousands to tens of thousands of antibodies and were derived from convalescent human donors, or vaccinated human donors or immunized mice. Here we used our technology to build a highly potent recombinant hyperimmune for Severe Acute Respiratory Syndrome Coronavirus-2 (SARS CoV-2) in less than three months. We also validated a recombinant hyperimmune for Zika virus disease that abrogates antibody-dependent enhancement (ADE) through Fc engineering. For patients with primary immune deficiency (PID), we built high potency polyvalent recombinant hyperimmunes against pathogens that commonly cause serious lung infections. Finally, to address the limitations of rabbit-derived anti-thymocyte globulin (ATG), we generated a recombinant human version and demonstrated in vivo function against graft-versus-host disease (GVHD). Recombinant hyperimmunes are a novel class of drugs that could be used to target a wide variety of other clinical applications, including cancer and autoimmunity.

immunology↗