Structural Dynamics Role of AGG Interruptions in Inhibition CGG Repeat Expansion Associated with Fragile X Syndrome

Abnormal expansion of trinucleotide CGG repeats is responsible for Fragile X syndrome. AGG interruptions in CGG repeat tracts were found in most healthy individuals, suggesting a crucial role in preventing disease-prone repeat expansion. Previous biophysics studies emphasize a difference in the secondary structure affected by AGG interruptions. However, the mechanism of how AGG interruptions impede repeat expansion remains elusive. We utilized single-molecule fluorescence resonance energy transfer spectroscopy to investigate the structural dynamics of CGG repeats and their AGG-interrupted variants. Tandem CGG repeats fold into a stem-loop hairpin structure with the capability to undergo a conformational rearrangement to modulate the length of the overhang. However, this conformational rearrangement is much more retarded when two AGG interruptions are present. Considering the significance of hairpin slippage in repeat expansion, we present a molecular basis suggesting that the internal loop created by two AGG interruptions acts as a barrier, obstructing the hairpin slippage reconfiguration. This impediment potentially plays a crucial role in curbing abnormal expansion, thereby contributing to the genomic stability.

Long-Range Hairpin Slippage Reconfiguration Dynamics in Trinucleotide Repeat Sequences

Trinucleotide repeat (TNR) sequences, which are responsible for several neurodegenerative genetic diseases, fold into hairpins that interfere with the protein machinery in replication or repair, thus leading to dynamic mutation -abnormal expansions of the genome. Despite their high thermodynamic stability, these hairpins can undergo configurational rearrangements, which may be crucial for continuous dynamic mutation. Here, we used CTG repeats as a model system to study their structural dynamics at the single-molecule level. A unique dynamic two-state configuration interchange was discovered over a wide range of odd-numbered CTG repeat sequences. Employing repeat-number-dependent kinetic analysis, we proposed a bulge translocation model, which is driven by the local instability and can be extended reasonably to longer (pathologically relevant) hairpins, implying the potential role in error accumulation in repeat expansion.

Giant chronic expanding hematoma in the chest identified 25 years after a blunt chest trauma

We herein report the case of a 42-year-old man who presented with a huge intrathoracic mass that had grown over a period of 25 years. The initial symptom caused by the mass was dull pain in the chest. T2-weighted magnetic resonance imaging revealed a mosaic pattern of various signal intensities, indicating a chronic expanding hematoma. The mass was completely resected surgically. For patients who present with a slowly growing mass, particularly those with a history of tuberculous pleuritis, chest surgery or trauma, a chronic expanding hematoma should be taken into consideration. Surgical resection is the first choice of treatment for a chronic expanding hematoma caused by a blunt chest trauma.

Slug overexpression is associated with poor prognosis in thymoma patients

Slug, a member of the Snail family of transcriptional factors, is a newly identified suppressive transcriptional factor of E-cadherin. The present study investigated the expression pattern of Slug in thymomas to evaluate its clinical significance. Immunohistochemistry was used to investigate the expression pattern of the Slug protein in archived tissue sections from 100 thymoma and 60 histologically normal thymus tissue samples. The associations between Slug expression and clinicopathological factors, such as prognosis, were analyzed. Positive expression of Slug was detected in a greater proportion of thymoma samples [51/100 (51%) patients, P<0.001] compared with normal thymus tissues [9/60 (15%) cases]. Of the 100 patients with thymoma, 42 (42%) displayed high levels of Slug expression (high-level group) and 58 (58%) displayed low levels of Slug expression (low-level group). The 10-year survival rate was improved for patients in the low-level group when compared with those in the high-level group (P=0.002). A multivariate analysis using the Cox proportional hazards regression model demonstrated that Slug overexpression was not an independent prognostic factor. In conclusion, the present study demonstrated that Slug overexpression was associated with poor prognosis in patients with thymoma. Therefore, Slug may be a potential diagnostic biomarker and a predictor of poor prognosis in thymoma patients.