一个基因的再引入（reintroduction）是什么意思

这是发表在Nature上的一篇文章《The common biology of cancer and ageing》中的话，原文是这样的——“Most adult cells have limiting amounts of telomerase that are not sufficient to prevent telomere loss, resulting in the shortening of telomeres with age[53]. As telomeres are essential for chromosomal stability, this progressive telomere loss was proposed to be at the basis of cellular senescence and ageing in the ‘telomere hypothesis’[53]. Indeed, telomere length has been shown to predict the replicative capacity of human cells and the appearance of certain age-associated pathologies in humans[54,55]. The final demonstration that telomere shortening was one of the causes of cellular senescence came from the observation that re-introduction of the TERT telomerase gene was sufficient to bypass replicative senescence and to confer immortal growth on a number of human primary cell lines[56]. Furthermore, the generation and characterization of the telomerase knockout mouse model has been instrumental in demonstrating