2025/10/31 by Myeonghoon Han, Baolong Xia, Ah‐Ram Kim +6 · 1 voice
Immunology and Microbiology · Neuroscience · Environmental Science · #Invertebrate Immune Response Mechanisms #Neurobiology and Insect Physiology Research #Bacteriophages and microbial interactions
paper · doi:10.1101/2025.10.31.685841
openalex publication_date 2025/10/31 · openalex created_date 2025/11/01 · openalex updated_date 2026/07/22
Abstract Circulating hormones, that mediate communications across organs to maintain physiological balance, are commonly detected and quantified using enzyme-linked immunosorbent assays (ELISAs). However, while ELISA is well-suited for organisms where sample blood can be readily obtained, its application is considerably more challenging in smaller organisms, particularly Drosophila , which has gained widespread use in recent years for physiological studies. Here, we present sensitive phage display-mediated immuno-PCR (PD-iPCR) to detect Drosophila hemolymph proteins via two approaches: 1) by identifying high-affinity nanobodies through phage-display library screening and subsequent affinity maturation and 2) by generating a knock-in fly line producing secreted proteins tagged with tandem NanoTags composed of VHH05 and 127D01. Using these approaches, we successfully established PD-iPCR to detect insulin-binding ImpL2 protein in fly hemolymph. Notably, the tandem NanoTag-based sandwich PD-iPCR enabled highly sensitive detection of tagged antigens, allowing us to quantify elevated ImpL2 levels in the hemolymph of starved flies and those bearing Yki -induced gut tumors. Collectively, our results demonstrate that PD-iPCR enables detection of endogenous, low-abundance circulating hormones in Drosophila , providing a powerful tool for studying interorgan communication. Significance statement Hormones and other secreted factors orchestrate organism-wide physiology, yet their routine quantification in Drosophila has been limited by the limited volume of hemolymph available for assays like enzyme-linked immunosorbent assay (ELISA). Here, we present phage display-mediated immuno-PCR (PD-iPCR) as a novel sensitive platform for quantifying secreted proteins in flies in vivo . Using ImpL2 as an example, we successfully detected nanomolar level of circulating ImpL2 and monitored its physiological changes during starvation and tumorigenesis using PD-iPCR. This approach can be readily expanded to multiplexed quantification of secreted proteins in vivo by leveraging the multiple available nanobodies and the vast collection of epitope-tagged Drosophila lines. This work opens the door to systematic endocrine phenotyping across developmental stages and diverse physiological conditions.