The molecular mechanisms involved in the genetic instability of the CCTG. CAGG repeats associated with myotonic dystrophy type 2
Year: 2006
Type: dissertation
Abstract: Myotonic dystrophy type 2 (DM2) is caused by the extreme expansion (from <\n30 repeats in normal individuals to ~ 11,000 for the full mutation in certain patients) of\nthe repeating tetranucleotide CCTG•CAGG sequence in the intron of the zinc finger\nprotein 9 (ZNF9) gene. The genetic instabilities of the CCTG•CAGG repeats were\ninvestigated to evaluate the molecular mechanisms responsible for these massive\nexpansions. The effects of replication, recombination, repair and transcription on the\ngenetic instabilities have been investigated in COS-7 cells and E. coli model systems. A\nreplication assay was established in COS-7 cells wherein the CCTG•CAGG repeats\ncloned proximal to the SV40 origin of replication resulted in expansions and deletions in\na length and orientation-specific manner, whereas the repeats cloned distal to the same\norigin were comparatively stable. These results fit with our data obtained from\nbiochemical studies on synthetic oligonucleotides since these biochemical studies\nrevealed that the d(CAGG)26 oligomer had a marked propensity to adopt a hairpin\nstructure as opposed to its complementary d(CCTG)26 that lacked this capacity. Furthermore, a genetic assay in E. coli was used to monitor the intramolecular frequency\nof recombination. This assay revealed that the tetranucleotide repeats were indeed hot\nspots for recombination. Moreover, studies conducted in SOS-repair mutants showed\nthat recombination frequencies were much lower in a SOS¯ strain as compared to a SOS+\nstrain. However, experiments conducted to ascertain the level of induction of the SOS\nresponse revealed that the SOS pathway was not stimulated in our studies. These results\nrevealed that although breaks may occur within the repeats, the damage is most likely\nrepaired without induction of the SOS response contrary to previous beliefs.\nThus, a complex interplay of replication, recombination, and repair is likely\nresponsible for the expansions observed in DM2.
Author: Ruhee Dere
Language: English
Subfield: Cellular and Molecular Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2243277861