Codon-optimized TDP-43 mediates neurodegeneration in a Drosophila model of ALS/FTLD

Outstretched wing is controlled by intestinal enteroblasts-derived unpaired 2 cytokine signaling in Drosophila

The outstretched wing phenotype in Drosophila melanogaster can be induced by various genetic mutations and environmental perturbations, yet the role of gut-derived signals in coordinating wing development remains largely unexplored. In this study, we demonstrate that Upd2, secreted from the gut to the wing discs, plays a crucial role in regulating the outstretched wing phenotype. The intestinal precursor cell driver esg-Gal4 exhibits low levels of leaky expression, even in the presence of Gal80ts at room temperature (25°C). This leaky expression of TDP-43, Notch, and Yki in intestinal precursor cells leads to a held-out wing phenotype, shortened lifespan, and impaired locomotor function. Although esg-Gal4 is expressed in imaginal discs, overexpression of TDP-43, Notch, or Yki using the wing-specific driver does not result in the outstretched wing. Furthermore, our data indicate that genetic alterations associated with the spread-out wing phenotype originate in enteroblasts (EBs) during early development. RNA sequencing analysis with guts from third instar larvae revealed that the JAK-STAT pathway ligand Upd2 is among the most significantly downregulated transcripts. Notably, ectopic expression of Upd2 in EBs partially rescued the abnormal held-out wing phenotype induced by TDP-43, Notch, and Yki overexpression. Together, our findings identify gut-derived Upd2 cytokine signaling as a key mediator of the outstretched wing phenotype, providing evidence for gut-to-wing communication axis during Drosophila development.

RNA aptamer reveals nuclear TDP-43 pathology is an early aggregation event that coincides with STMN-2 cryptic splicing and precedes clinical manifestation in ALS

TDP-43 is an aggregation-prone protein which accumulates in the hallmark pathological inclusions of amyotrophic lateral sclerosis (ALS). However, the analysis of deeply phenotyped human post-mortem samples has shown that TDP-43 aggregation, revealed by standard antibody methods, correlates poorly with symptom manifestation. Recent identification of cryptic-splicing events, such as the detection of Stathmin-2 (STMN-2) cryptic exons, are providing evidence implicating TDP-43 loss-of-function as a potential driving pathomechanism but the temporal nature of TDP-43 loss and its relation to the disease process and clinical phenotype is not known. To address these outstanding questions, we used a novel RNA aptamer, TDP-43APT, to detect TDP-43 pathology and used single molecule in situ hybridization to sensitively reveal TDP-43 loss-of-function and applied these in a deeply phenotyped human post-mortem tissue cohort. We demonstrate that TDP-43APT identifies pathological TDP-43, detecting aggregation events that cannot be detected by classical antibody stains. We show that nuclear TDP-43 pathology is an early event, occurring prior to cytoplasmic accumulation and is associated with loss-of-function measured by coincident STMN-2 cryptic splicing pathology. Crucially, we show that these pathological features of TDP-43 loss-of-function precede the clinical inflection point and are not required for region specific clinical manifestation. Furthermore, we demonstrate that gain-of-function in the form of extensive cytoplasmic accumulation, but not loss-of-function, is the primary molecular correlate of clinical manifestation. Taken together, our findings demonstrate implications for early diagnostics as the presence of STMN-2 cryptic exons and early TDP-43 aggregation events could be detected prior to symptom onset, holding promise for early intervention in ALS.