The telomeric transcriptome and SMG proteins at the crossroads.

Telomeres constitute the heterochromatic structures at the ends of linear eukaryotic chromosomes and are essential for the maintenance of genome stability. The longstanding belief that telomeres are transcriptionally silent has recently been overturned by the discovery of a telomeric transcriptome comprising telomeric repeat-containing RNA (TERRA) molecules. In mammalian cells, TERRA remains associated with telomeres after its transcription, and this association is regulated by SMG proteins, renowned for their involvement in several RNA metabolism pathways. The three SMG factors UPF1, hEST1A and SMG1, which have been associated with DNA stability networks before, also seem to be crucial to guarantee telomere integrity. Here, we review the current knowledge available of TERRA and on the role of SMG proteins in maintaining genome stability. We also propose an integrative model illustrating a putative link between telomere integrity, TERRA and SMG proteins. Copyright 2008 S. Karger AG, Basel.