Fig. 5

In vivo functional assays showing that telomerase depletion leads to impaired phagocytosis in gut mpeg + cells and increased gut permeability. The mpeg1.1: mcherry caax transgenic zebrafish line was used to quantify A in vivo phagocytosis in the gut, of E. coli pHrodo (green) bioparticles by mpeg + cells (red). E. coli pHrodo bioparticles were delivered to the gut via gavage. Phagocytosed E. coli pHrodo bioparticles will fluoresce green inside mcherry caax⁺ phagosomes, inside mpeg⁺ cells. A1 Shows representative images of young (c.5 months old) WT or tert^−/− zebrafish gut cryostat sections, displaying native mcherry (mpeg⁺ cells) and green fluorescence (E. coli pHrodo bioparticles). Nuclei were counterstained with DAPI (blue), and scale bars represent 50 mm. Yellow arrows in A1 point to examples of mpeg⁺ cells (red) with phagocytosed E. coli bioparticles within. A2 Shows quantification of the % of mpeg⁺ cells with E. coli bioparticles inside, as a readout of phagocytosis efficiency. B) in vivo gut permeability assay (Smurf assay). WT and tert.^−/− of different ages were assessed for gut permeability by adding blue dye to the water for 30 min and then washing out extensively. Any fish developing an extensive blue coloration in their body indicate that the blue dye permeated through the gut and were therefore considered “smurfs”. B1 Quantification of the percentage of “smurfs” (blue bars) per genotype. Young animals are c. 5 months old, old WT are > 30 months old and “old” tert-/- are > 12 months old, as further explained in materials and methods