Abstract: FR-PO0763
Deciphering the Mechanistic Role of Formin Disheveled Associated Activator of Morphogenesis 2 (DAAM2) in Podocytes Using Drosophila Nephrocytes
Session Information
- Glomerular Diseases: Cell Homeostasis and Novel Injury Mechanisms
November 07, 2025 | Location: Exhibit Hall, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Glomerular Diseases
- 1401 Glomerular Diseases: Mechanisms, including Podocyte Biology
Authors
- Lang, Konrad, Medical Center - University of Freiburg, Freiburg, Germany
- Wiggering, Jost, Medical Center - University of Freiburg, Freiburg, Germany
- Milosavljevic, Julian, Medical Center - University of Freiburg, Freiburg, Germany
- Comas Soberats, Maria, Medical Center - University of Freiburg, Freiburg, Germany
- Hermle, Tobias F., Medical Center - University of Freiburg, Freiburg, Germany
Group or Team Name
- AG Hermle.
Background
The cellular structure of podocytes requires precisely regulated actin dynamics. Formins such as INF2 and DAAM2 nucleate actin via their FH2 domain. DAAM2 adopts an autoinhibited conformation that is primarily relieved by Rho GTPases. Mutations in DAAM2 and INF2 have been identified as monogenic causes of hereditary steroid-resistant nephrotic syndrome. INF2 was linked to nephrin trafficking and nuclear F-actin assembly, but the role of DAAM2 is less clear. DAAM2 silencing impairs podocyte migration and filopodia formation, and co-localization with INF2 suggests possible cooperative functions in cytoskeletal regulation.
Methods
To investigate the role of DAAM2, we used the Drosophila model. Drosophila nephrocytes form an evolutionarily conserved slit diaphragm that is easily accessible. We examined these cells through immunofluorescence and live antibody labeling experiments as well as electron microscopy after silencing of Daam, the Drosophila ortholog of DAAM2. Additionally, we generated transgenes of known human DAAM2 variants to assess their function in Drosophila.
Results
Following Daam silencing in Drosophila nephrocytes, we observed increased spacing between slit diaphragms, indicating a reduction of protein levels for fly nephrin (Sns). Live antibody labeling indicated that Daam silencing accelerated the endocytic turnover of fly nephrin, suggesting potential destabilization of the slit diaphragm. We further noted increased basal autophagy, indicated by reduction in Atg8a-GFP, which may contribute to the accelerated nephrin turnover. RNA sequencing upon silencing of Daam revealed upregulation of mthl8, a GPCR likely linked to autophagy, suggesting a possible connection between the observed phenotypes. Notably, silencing of mthl8 similarly decreased density of slit diaphragms. The overexpression of human DAAM in nephrocytes further led to widened slit distances, suggesting a potential dominant negative effect, which was aggravated with patient-derived, known pathogenic variants.
Conclusion
DAAM2 plays a role for maintaining proper slit diaphragm architecture. Its absence destabilizes nephrin and alters basal autophagy. Transgenesis of human DAAM2 in Drosophila nephrocytes provides functional insight for DAAM2 variants.
Funding
- Government Support – Non-U.S.