The deterioration of T1 neurons during ageing is independent of temperature and marker expression.

(A–D) T1 axons (top) and synaptic terminals (bottom) in the medulla of flies labelled with the plasma membrane marker myr-Tom (myr) using the UAS/Gal4/Gal80^ts system. Gene expression is induced by the shift of temperature from 18°C to 29°C. Flies were kept at 18°C throughout development and adult life until the last 4 days before imaging, at which point they were shifted to 29°C to induce myr-Tomato gene expression. Young specimens (A and C; 4–7 days old flies with 0–3 days at 18°C “Off” + 4 days at 29°C “On”) are compared to old specimens (B and D; 57–60 days old flies with 53–56 days at 18°C “Off” + 4 at 29°C “On”). In aged specimens, axons show thinning (arrowheads) and swellings (asterisks), whereas synaptic terminals appear swollen and broken down (arrows and dashed blue box shown as 3-fold magnified image in the inset below). (E) Quantifications of phenotypes shown in A–D, with young versus old indicated on the X-axes. In the top 2 graphs, data points are shown in blue and as mean bars ± SEM (p-values obtained via Mann–Whitney test are indicated above). For terminal morphology, data are shown as distribution of normal versus swollen/broken synapses (significance obtained via Chi-square test indicated above). Data were taken from a minimum of 5 specimens per age group. For detailed statistical values and genotypes, see Table C within the S1 Tables. All the single values are provided in the S1 Datapoints. Scale bar in A represents 20 μm in all images.

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