AUXIN-INDUCED DEGRADATION OF DREAM PROTEINS, LIN-9 AND LIN-54, IN CAENORHABDITIS ELEGANS

The Dp, Retinoblastoma, E2F, And MuvB (DREAM) complex mediates transcriptional repression and is highly conserved throughout a number of species, including vertebrates, Drosophila melanogaster, and Caenorhabditis elegans. Differing from mammalian DREAM, C.elegans DRM, appears to act solely in a repressive role, with the MuvB subcomplex (LIN-9, LIN-37, LIN-52, LIN-53, and LIN-54) playing a key role in the repression of genes. In this study, we use the auxin-inducible degron (AID) system, an effective, fast-acting, tool used in the degradation of degron-tagged proteins to individually deplete two key proteins of the MuvB subcomplex, LIN-9 and LIN-54, in C. elegans. The AID system relies on the expression of the F-box protein, transport inhibitor response 1 (TIR1), which in the presence of auxin acts as the substrate recognition component for the SKP1-CUL1-F-box (SCF) E3 ubiquitin ligase complex, leading to the degradation of tagged proteins. In degron-tagged LIN-54 worms, using a 6-hour auxin time course, we observed that DREAM target genes become significantly upregulated. Expression of DREAM target genes increased with longer exposure to auxin, indicating that LIN-54 plays a key role in the regulation of DREAM target genes. However, in both a 6-hour and 24-hour auxin time course experience, degron-tagged LIN-9 worms showed no uniform nor significant upregulation of DREAM target genes compared to ethanol vehicle control. These results demonstrate that LIN-54, the sole DNA-binding protein of MuvB, plays a more important role in MuvB’s repression of genes than the core protein of MuvB, LIN-9. We recommend further study into these two proteins using the AID system to further explore their roles in MuvB and DREAM complex function

Biomechanical evaluation of predictive parameters of progression in adolescent isthmic spondylolisthesis: a computer modeling and simulation study

<p>Abstract</p> <p>Background</p> <p>Pelvic incidence, sacral slope and slip percentage have been shown to be important predicting factors for assessing the risk of progression of low- and high-grade spondylolisthesis. Biomechanical factors, which affect the stress distribution and the mechanisms involved in the vertebral slippage, may also influence the risk of progression, but they are still not well known. The objective was to biomechanically evaluate how geometric sacral parameters influence shear and normal stress at the lumbosacral junction in spondylolisthesis.</p> <p>Methods</p> <p>A finite element model of a low-grade L5-S1 spondylolisthesis was constructed, including the morphology of the spine, pelvis and rib cage based on measurements from biplanar radiographs of a patient. Variations provided on this model aimed to study the effects on low grade spondylolisthesis as well as reproduce high grade spondylolisthesis. Normal and shear stresses at the lumbosacral junction were analyzed under various pelvic incidences, sacral slopes and slip percentages. Their influence on progression risk was statistically analyzed using a one-way analysis of variance.</p> <p>Results</p> <p>Stresses were mainly concentrated on the growth plate of S1, on the intervertebral disc of L5-S1, and ahead the sacral dome for low grade spondylolisthesis. For high grade spondylolisthesis, more important compression and shear stresses were seen in the anterior part of the growth plate and disc as compared to the lateral and posterior areas. Stress magnitudes over this area increased with slip percentage, sacral slope and pelvic incidence. Strong correlations were found between pelvic incidence and the resulting compression and shear stresses in the growth plate and intervertebral disc at the L5-S1 junction.</p> <p>Conclusions</p> <p>Progression of the slippage is mostly affected by a movement and an increase of stresses at the lumbosacral junction in accordance with spino-pelvic parameters. The statistical results provide evidence that pelvic incidence is a predictive parameter to determine progression in isthmic spondylolisthesis.</p