The t-loop model proposed in our laboratory by Dr. Griffith was based on the long history of this laboratory on recA driven recombination and is supported by a large and growing body of research. However, despite the advances of the last decade, the mechanism underlying t-loop formation remains poorly understood. While the shelterin factor TRF2 has been shown to promote t-loop formation in vitro, it remains unknown to what degree TRF2 and the other shelterin factors are necessary in vivo. Indeed seems unlikely that TRF2 alone is sufficient to catalyze t-loop formation in vivo given the presence of nucleosomes and an intact shelterin complex in a physiological context.
It is reasonable to assume that the process of t-loop formation is driven by homologous recombination machinery, as the process of telomere maturation and capping occur during and immediately following S-Phase; a time when HR proteins are at relatively high concentration. Indeed, this notion is supported in part by the observation that BRCA2 recruits Rad51 to telomeres in a cell-cycle specific manner, and that disruption of this process results in telomere erosion and dysfunction. However, it remains unclear whether this erosion and dysfunction are due to a capping deficiency (e.g. failure to form a t-loop) or due to replication stress (i.e. failure to resolve stalled replication forks).
Using a variety of techniques and several reagents from our collaborators I am working to determine whether a mixture of factors including BRCA2 and Rad51 are able to produce t-loops in model telomeres in the presence of a variety of shelterin components and other proteins.