Differences in telomere length and telomerase gene expression with age and among tissues in the Pacific oyster

Marine organisms are continuously exposed to chemical stressors, highlighting the need for operational biomarkers that can be reliably implemented in biomonitoring programmes. Telomere length (TL) has emerged as a promising biomarker of cumulative stress, but its application in ecotoxicology remains limited due to two main challenges: (i) methodological difficulties in obtaining reliable TL measurements from preserved samples, and (ii) incomplete understanding of telomere dynamics across tissues and life stages in sentinel marine species. In this study, we addressed both limitations in the Pacific oyster Crassostrea gigas. First, we compared different DNA extraction methods and selected a protocol suitable for isolating high-molecular-weight DNA from frozen oyster tissues. The qPCR assay was then optimized to minimise technical biases and ensure accurate TL quantification. Using this optimized method, we assessed TL variation across tissues and age classes. Significant tissue-specific differences were observed, with the digestive gland exhibiting the shortest telomeres. In addition, a clear age-related decrease in TL was detected across all tissues. Finally, RT-qPCR analyses revealed lower expression of the telomerase gene in adult tissues compared to early developmental stages, in line with the absence of detectable telomerase activity in adults. Together, these findings provide a methodological and biological framework for future investigations into the effects of chemical stress on telomere dynamics in oysters.