Reconstitution of active telomerase in primary human foreskin fibroblasts: effects on proliferative characteristics and response to ionizing radiation

Purpose: Telomere shortening has been proposed to trigger senescence, and since most primary cells do not express active telomerase, reactivation of telomerase activity was proposed as a safe and non-transforming way of immortalizing cells. However, to study radiation responses, it is as yet unclear whether cells immortalized by telomerase reactivation behave in a similar manner as their parental primary cells. Materials and methods: Primary human foreskin fibroblasts were transfected with the human catalytic subunit of telomerase, the reverse transcriptase (hTERT), and their growth characteristics and response to DNA damage were characterized. Results: The sole expression of the human hTERT was sufficient to immortalize the human foreskin fibroblasts. With time in culture, the immortalized cells almost doubled their average telomeric length and the clonal population contained almost no post-mitotic fibroblasts anymore. Up to 300 population doublings, no alterations compared with the parental primary cells were seen in terms of clonogenic radiosensitivity, DNA double-strand break repair, radiation-induced increases in p53 and p21WAF-1,CIP-1 expression, and the G1/S and G2/M cell cycle checkpoints. Moreover, mitogen-induced mitotic arrest of fibroblasts was still possible in the hTERT-immortalized clones. Conclusions: Immortalizing fibroblasts by reconstitution of active telomerase seems a good, reliable manner to generate a large source of cells with a radiation damage response similar to the primary cells

Impact evaluation and interventions to address climate change:a scoping study

Substantial and increasing amounts of funding are available for countries to undertake climate change interventions. This article argues that to ensure effective allocation of these resources, the selection and design of climate change mitigation and adaptation interventions should be based on evidence of what works, what doesn't work, under what circumstances and at what cost. Currently the evidence base on the impact of climate change interventions is minimal and there is a need for wider application of rigorous impact evaluation (IE) in the field. Climate change interventions have much to learn from experiences in related fields, notably international development and conservation. The paper highlights some of the challenges faced when conducting IEs of climate change interventions and discusses how these can be tackled. Moreover, it discusses some of the key areas of mitigation and adaptation interventions and suggests how IEs could be implemented, using IEs from other policy fields as examples. It argues that despite the limited experience so far there are ample opportunities to conduct IE of climate change interventions. If calls for increasing financing of climate change mitigation and adaptation by hundreds of billions of dollars a year are to remain credible and gain support, evidence of the effectiveness of current spending is essential