Two DNA-encoded strategies for increasing expression with opposing effects on promoter dynamics and transcriptional noise.

Individual cells from a genetically identical population exhibit substantial variation in gene expression. A significant part of this variation is due to noise in the process of transcription that is intrinsic to each gene, and is determined by factors such as the rate with which the promoter transitions between transcriptionally active and inactive states, and the number of transcripts produced during the active state. However, we have a limited understanding of how the DNA sequence affects such promoter dynamics. Here, we used single-cell time-lapse microscopy to compare the effect on transcriptional dynamics of two distinct types of sequence changes in the promoter that can each increase the mean expression of a cell population by similar amounts but through different mechanisms. We show that increasing expression by strengthening a transcription factor binding site results in slower promoter dynamics and higher noise as compared with increasing expression by adding nucleosome-disfavoring sequences. Our results suggest that when achieving the same mean expression, the strategy of using stronger binding sites results in a larger number of transcripts produced from the active state, whereas the strategy of adding nucleosome-disfavoring sequences results in a higher frequency of promoter transitions between active and inactive states. In the latter strategy, this increased sampling of the active state likely reduces the expression variability of the cell population. Our study thus demonstrates the effect of cis-regulatory elements on expression variability and points to concrete types of sequence changes that may allow partial decoupling of expression level and noise.

Comparison of functional outcomes of reverse shoulder arthroplasty versus hemiarthroplasty in the primary treatment of acute proximal humerus fracture.

BACKGROUND: Treatment of complex proximal humeral fractures remains controversial. In cases where adequate open reduction and internal fixation cannot be achieved, hemiarthroplasty has been the traditional treatment; however, clinical results have been mixed. Reverse shoulder arthroplasty (RSA) has been suggested as an alternative, and this study aimed to compare the functional results of RSA versus hemiarthroplasty in patients with acute proximal humeral fracture. METHODS: Ten patients with acute proximal humerus fractures unsuitable for internal fixation (mean age 77) who underwent RSA for acute proximal humerus fracture unsuitable for internal fixation against the outcomes of 10 patients (mean age 75) who had previously undergone hemiarthroplasty for the same indication. Functional scores and radiographic outcomes were assessed at 22-44 months follow up. RESULTS: At follow up the mean American Shoulder and Elbow Scorev score was 65 (range 40-88) in the RSA group and 67 (26-100) in the hemiarthroplasty group. Mean Oxford Shoulder scores were 29 (15-56) and 22 (12-34), respectively. Mean forward elevation was 115 degrees (range 45-140 degrees) and active external rotation was 49 degrees (5-105 degrees) in the RSA group, versus 108 degrees (50-180 degrees) and 48 degrees (10-90 degrees) in the hemiarthroplasty group. No statistically significant differences in outcome scores or range of motion were seen. CONCLUSION: In these early results, the anticipated functional gains of RSA over hemiarthroplasty were not realized, suggesting the use of RSA for treatment of proximal humeral fractures should remain guarded. Larger prospective trials are necessary to identify the optimal management of patients in this situation.