Effects of distraction-based distal fixation on pelvic parameter development in early onset scoliosis.

PURPOSE: Prior studies have suggested that distraction-based treatment for early onset scoliosis (EOS) may impede the natural development of the sagittal spinal alignment and pelvic parameters. However, to date no study has investigated the effect of distal fixation on pelvic development. METHODS: Ambulatory children with EOS undergoing index distraction-based treatment with distal fixation below T11 were retrospectively reviewed. Patients with distal fixation to the pelvis were identified and compared to children with Spine-based fixation at T12-L5. Radiographic measurements were performed for coronal and sagittal alignment in addition to pelvic parameters (pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS) and compared at initial presentation, first erect radiograph, and at 2 years following instrumentation. RESULTS: 33 ambulatory children were identified with a minimum of 2-year follow-up (25 female, average 6.59 ± 2.6 years), with 33% (N = 11) instrumented to the pelvis (54.4% female, average 4.42 ± 2.2 years, initial Cobb 76.1°). Children in the pelvis cohort were significantly younger at treatment initiation (P < 0.001). There was no significant difference in PI at the study time periods, however, there was a significant change in PI between presentation and 2-year follow-up with the pelvic fixation demonstrating a mean 12.3° decrease in PI vs a 3.8° increase in the spine-based cohort (P = 0.027). DISCUSSION: Distal fixation to the pelvis in ambulatory children with EOS treated with growth-friendly instrumentation was associated with a mean decrease in PI of 12.3° that developed over the 2-year treatment duration. Further research is needed to investigate the long-term implications of these findings on pelvic and spinal development.

A Cell Density-Dependent Reporter in the Drosophila S2 Cells.

Cell density regulates many aspects of cell properties and behaviors including metabolism, growth, cytoskeletal structure and locomotion. Importantly, the responses by cultured cells to density signals also uncover key mechanisms that govern animal development and diseases in vivo. Here we characterized a density-responsive reporter system in transgenic Drosophila S2 cells. We show that the reporter genes are strongly induced in a cell density-dependent and reporter-independent fashion. The rapid and reversible induction occurs at the level of mRNA accumulation. We show that multiple DNA elements within the transgene sequences, including a metal response element from the metallothionein gene, contribute to the reporter induction. The reporter induction correlates with changes in multiple cell density and growth regulatory pathways including hypoxia, apoptosis, cell cycle and cytoskeletal organization. Potential applications of such a density-responsive reporter will be discussed.

Chromatin boundary elements organize genomic architecture and developmental gene regulation in Drosophila Hox clusters.

The three-dimensional (3D) organization of the eukaryotic genome is critical for its proper function. Evidence suggests that extensive chromatin loops form the building blocks of the genomic architecture, separating genes and gene clusters into distinct functional domains. These loops are anchored in part by a special type of DNA elements called chromatin boundary elements (CBEs). CBEs were originally found to insulate neighboring genes by blocking influences of transcriptional enhancers or the spread of silent chromatin. However, recent results show that chromatin loops can also play a positive role in gene regulation by looping out intervening DNA and "delivering" remote enhancers to gene promoters. In addition, studies from human and model organisms indicate that the configuration of chromatin loops, many of which are tethered by CBEs, is dynamically regulated during cell differentiation. In particular, a recent work by Li et al has shown that the SF1 boundary, located in the Drosophila Hox cluster, regulates local genes by tethering different subsets of chromatin loops: One subset enclose a neighboring gene ftz, limiting its access by the surrounding Scr enhancers and restrict the spread of repressive histones during early embryogenesis; and the other loops subdivide the Scr regulatory region into independent domains of enhancer accessibility. The enhancer-blocking activity of these CBE elements varies greatly in strength and tissue distribution. Further, tandem pairing of SF1 and SF2 facilitate the bypass of distal enhancers in transgenic flies, providing a mechanism for endogenous enhancers to circumvent genomic interruptions resulting from chromosomal rearrangement. This study demonstrates how a network of chromatin boundaries, centrally organized by SF1, can remodel the 3D genome to facilitate gene regulation during development.