Fig. 3

WT zebrafish gut mpeg⁺ cells express telomerase but this decreases with ageing and is accompanied by telomere shortening. The mpeg1.1: mcherry caax transgenic zebrafish line was used to A detect telomerase (tert), by RNA in situ hybridisation (white) and PCNA expression in gut mpeg⁺ cells in young and old WT zebrafish paraffin sections. A1 Quantification the % of mpeg⁺ with tert expression and no PCNA expression (green) and the % of mpeg⁺ cells with PCNA expression (magenta). Yellow arrows are pointing to a mpeg⁺ cell example (in green), that is expressing tert (white dots) and that is either PCNA negative (top) or PCNA positive (bottom) In B The relative % of mpeg⁺ cells with telomerase are compared between the gut and the head kidney of young WT fish. C The mpeg1.1: mcherry caax transgenic zebrafish line was used to detect telomeres using Telo-FISH (red), Cent-FISH (white) combined with anti-RFP (in green) to detect mpeg⁺ cells young and old WT zebrafish paraffin sections. Yellow arrows here are pointing to mpeg⁺ cells (green) identified in the panel showing mpeg and arrows were kept when the other channels are displayed for ease of identification of where the mpeg⁺ cells would be. Merged channels can be seen in the last panel on the right. C1 Shows the relative quantification of telomere length (tel/cent ratio) in gut mpeg⁺ cells in WT young and old, compared to young tert.^−/− zebrafish. C2 Shows the % of gut mpeg + cells with “hyper-long” telomeres. Young animals are c.5 months old and old animals are > 30–36 months old. Nuclei are counterstained with DAPI (blue). All scale bars represent 50 µm unless otherwise stated in the figure