ABSTRACT
Magnetic resonance imaging (MRI) may be the most sensitive modality for detecting post-traumatic degeneration of articular cartilage. Magnetic resonance imaging must accurately depict articular cartilage in the presence of periarticular fracture stabilization devices to be effective for postoperative imaging of articular fractures. This study examines how close titanium screws can be inserted to tibial articular surfaces and still allow accurate MRI of the overlying articular cartilage. Cannulated titanium screws were inserted at varying distances from subchondral bone in the proximal and distal tibiae of embalmed human cadaveric legs, which were then imaged using a standard nonfat-saturated fast low angle shot two-dimensional sequence (FLASH 2D). The distance from the center of the screw to the subchondral bone and the thickness of the articular cartilage directly overlying the screw was then determined by direct measurement and by measurement on the scanned images. To allow FLASH 2D MRI of the articular cartilage, 7.3-mm screws had to be at least 13 mm from the subchondral bone, and 4.5-mm screws had to be at least 12 mm from the subchondral bone. For MRI to be effective for the postoperative imaging of the articular surface following severe articular fractures of the tibia, titanium fracture hardware must be farther away from the articular surface than these minimum distances. Alternate materials for stabilizing articular fractures are available and may allow clearer and more accurate imaging of the articular cartilage when inserted close to the articular surface.
Subject(s)
Bone Screws , Cartilage, Articular/anatomy & histology , Cartilage, Articular/surgery , Magnetic Resonance Imaging , Titanium , Cadaver , HumansSubject(s)
Anti-Bacterial Agents/therapeutic use , Meningitis, Bacterial/drug therapy , Pneumococcal Infections/drug therapy , Streptococcus pneumoniae/drug effects , Vancomycin/therapeutic use , Adolescent , Arkansas/epidemiology , Bacteremia/drug therapy , Bacteremia/microbiology , Child , Drug Resistance, Microbial , Female , Humans , Infant , Male , Meningitis, Aseptic/diagnosis , Meningitis, Aseptic/drug therapy , Meningitis, Aseptic/microbiology , Meningitis, Bacterial/epidemiology , Meningitis, Bacterial/microbiology , Missouri/epidemiology , Seasons , Streptococcus pneumoniae/isolation & purification , Vancomycin/pharmacologyABSTRACT
Despite their descent from a common ancestral gene and the requirement for coordinated, tissue-specific regulation, the alpha- and beta-globin genes in many mammals are regulated in distinctly different ways. Unlike the beta-globin gene, the rabbit alpha-globin gene is transiently expressed at a high level without an added enhancer in transfected erythroid and non-erythroid cells. By examining a series of alpha/beta fusion genes, we show that internal sequences of the rabbit alpha-globin gene (within the first two exons and introns) are required along with the 5' flank for this enhancer-independent expression. Furthermore, deletion of the introns of the alpha-globin gene, or replacement by introns of the beta-globin gene, results in severely decreased expression of the transfecting genes. Hybrid constructs between segments of the alpha-globin gene and a luciferase gene confirm that internal alpha-globin sequences are needed for high level production of RNA in transfected cells. The flanking and internal sequences implicated in regulation of the rabbit alpha-globin gene coincide with a prominent CpG-rich island and may comprise an extended promoter (including both flanking and intragenic sequences) that is active in transfected cells without an enhancer.
Subject(s)
Gene Expression Regulation/genetics , Globins/genetics , Regulatory Sequences, Nucleic Acid , Animals , Binding Sites , Cloning, Molecular , DNA-Binding Proteins/metabolism , Enhancer Elements, Genetic , Erythroid-Specific DNA-Binding Factors , Genes , Humans , Luciferases/genetics , Promoter Regions, Genetic , RNA/biosynthesis , Rabbits , Sequence Deletion , Simian virus 40/genetics , Sp1 Transcription Factor/metabolism , Transcription Factors/metabolism , Transcription, Genetic , Transfection , Tumor Cells, CulturedABSTRACT
The epsilon-globin genes of mammals are expressed in early embryos, but are silenced during fetal and adult erythropoiesis. As a guide to defining the regulatory elements involved in this developmental switch, we have searched the sequences of epsilon-globin genes from different mammals for highly conserved segments. The search was facilitated by the development of a new program, called yama, to generate a multiple alignment of very long sequences using an improved scoring scheme. This allowed us to generate a multiple alignment of sequences from a more divergent group than previously analyzed, as demonstrated here for representatives of four mammalian orders. In parallel experiments, we constructed a series of deletion mutations in the 5' flank of the rabbit epsilon-globin gene and tested their effect on an epsilon-globin-luciferase hybrid reporter gene. These results show that 121 bp of 5' flank, containing CACC, CCAAT and ATA motifs, is sufficient for expression in erythroid K562 cells. Both positive and negative cis-acting control sequences are located between 218 and 394 bp 5' to the cap site, in a region previously proposed to be a silencer. The positive regulatory sequence contains conserved binding sites for the nuclear protein YY1 adjacent to another highly conserved sequence. The negative element contains a conserved sequence followed by a purine-rich segment. This analysis maps the upstream control sequences more precisely and points to a very complex regulatory scheme for this gene.
