Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Septic superficial thrombophlebitis: a major threat from a minor lesion

Sites of insertion of peripheral intravenous catheters remain an important but often overlooked source of hospital-acquired septicemia and the most important source of staphylococcal septicemia. Septic superficial thrombophlebitis is characterized by severe local pain and is readily evident clinically. Care of the intravenous line can prevent this complication. To be diagnosed, it must be suspected. Treatment consists of removal of the intravenous line and administration of heparin and antibiotics effective against penicillinase-producing organisms. Occasionally the vein must be ligated or, preferably, removed.     

Automated Chemical Synthesis of PNA and PNA-DNA Chimera on a Nucleic Acid Synthesizer

Abstract

Automated chemical synthesis of PNA and PNA-DNA chimera on a DNA synthesizer using the monomethoxytrityl/acyl protecting group strategy is described.     

Synthesis of Anti-Sense Phosphorothioate Analogues for Pharmacokinetic and Pre-Clinical Studies

Abstract

Nudease-resistant oligonucleotides (11 to 28-mers) containing stereorandom phosphorothioate linkages have been recently reported to exhibit potent anti-HIV III effects and sequence-specific inhibition of protein synthesis. Relatively large amounts (100 mg 1g) of these analogues. which are needed for further biological testing and initial pharmacokinetic and pre-clinical studies, were readily obtained by automated hydrogen phosphonate chemistry followed by reversed-phase HPLC and further processing. This chemistry features 1 -adamanetanecarbonyl chloride as the activator, capping with isopropyl phosphite, and more complete sulfurization in only one-step following chain assembly. An automated, quantitative. picomole method for analysis of the analogues in blood samples has been developed.     

The nature of different influence of Cd<Superscript>2+</Superscript> ions on the conformational equilibrium of triple-stranded polyribonucleotides poly(U)•poly(A)•poly(U) and poly(I)•poly(A)•poly(I) in aqueous solutions

The influence of Cd²⁺ ions on the conformational equilibrium of single-stranded (poly(U), poly(A), poly(I)) and triple-stranded polyribonucleotides (A2I, A2U) in aqueous solutions (0.1 M Na⁺ pH 7) has been investigated using difference UV spectroscopy and thermal denaturation. Analysis of the shape and intensity of the DUV spectra of poly(A), poly(I), and A2I has revealed the presence of two types of complex formed as a result of (i) interaction between Cd²⁺ and the N7 atoms of purines, producing macrochelates; and (ii) binding of Cd²⁺ to the N1 atoms of poly(A) and poly(I). Since Cd²⁺ ions are not bound to heteroatoms of the bases in A2U, the conformation of the structure remains stable up to 0.02 M Cd²⁺. There is a critical Cd²⁺ concentration (～1.5?10^?4 M) above which A2I assumes a new helical conformation with lower thermal stability. It is supposed that, upon the formation of the “metallized” A2I triplex, the Cd²⁺ ions are located inside the triple helix and form bridges between the hypoxanthine and adenine of the homopolynucleotide strands.     

What can we learn from noncoding regions of similarity between genomes?

Background  

In addition to known protein-coding genes, large amounts of apparently non-coding sequence are conserved between the human and mouse genomes. It seems reasonable to assume that these conserved regions are more likely to contain functional elements than less-conserved portions of the genome.     

The effect of low-molecular-weight heparin in the survival of a rabbit congested skin flap

Swelling and congestion of flaps are frequently seen postoperatively and can cause unexpected necrosis. According to previous reports, venous thrombosis seems to be a more frequent problem than arterial occlusion in both experimental and clinical surgery. Few satisfactory venous trauma models exist, and reports on experimental venous thrombosis are rare. The object of this study was to create a rabbit venous occlusion flap model and to evaluate the effect of low-molecular-weight heparin on this flap. Eight New Zealand rabbits were used in the pilot study, in which the ideal congested flap was investigated using a flap pedicle based on the central auricular artery with a skin pedicle 0, 1, 2, or 3 cm wide. The flap (3 x 6 cm) was designed on the central part of the left ear, and the central auricular vein and nerve, the former for venous return, were cut out at the base of the flap. The flaps with skin pedicles 0, 1, 2, or 3 cm wide showed mean necrosis length of 60.0, 9.3, 4.2, and 0.0 mm, respectively. The flaps with skin pedicles 0, 1, 2, or 3 cm wide showed mean necrosis of 100, 15.5, 7, and 0 percent, respectively. Therefore, the flap, based on a 1-cm-wide skin pedicle and the central auricular artery, was selected as an optimal congested flap model showing 15.5 percent necrosis. The congested flap was then elevated on the left ear of another 10 rabbits. Subcutaneous low-molecular-weight heparin (320 IU/kg) was administered immediately after surgery to five of the rabbits (the low-molecular-weight heparin group), and the remaining five were used as a control group. Fluorescein was injected 15 minutes after surgery to evaluate the circulatory territory of the flap, and the circulatory territory was measured 5 minutes after injection. The flaps were assessed 7 days after surgery by angiography, histology, and clinical findings. The circulatory territory was significantly greater in the low-molecular-weight heparin group (mean +/- SD, 39.2 +/- 3.0 mm) than the control group (mean +/- SD, 48.0 +/- 1.0 mm) (p < 0.001) assessed 7 days after surgery. The longest flap survival length in group A and group B ranged from 40 to 55 mm (mean +/- SD. 49.4 +/- 5.6 mm) and complete survival (mean +/- SD, 60.0 +/- 0.0 mm). The improvement in survival was statistically significant for group B compared with group A (p < 0.015). Histologic evaluation revealed moderate to severe venous congestion and inflammation in the control group, whereas there were minimal changes in the low-molecular-weight heparin group. Angiography of the flap revealed obvious venous occlusion in the periphery in the control group compared with the low-molecular-weight heparin group. The authors conclude that subcutaneous administration of low-molecular-weight heparin has a great potential to improve the survival length of a congested flap without major complications.