Frankenswine,or bringing home the bacon: How close are we to clinical trials in xenotransplantation?

Xenotransplantation—specifically from pig into human—could resolve the critical shortage of organs, tissues and cells for clinical transplantation. Genetic engineering techniques in pigs are relatively well-developed and to date have largely been aimed at producing pigs that either (1) express high levels of one or more human complement-regulatory protein(s), such as decay-accelerating factor or membrane cofactor protein, or (2) have deletion of the gene responsible for the expression of the oligosaccharide, Galα1,3Gal (Gal), the major target for human anti-pig antibodies, or (3) have both manipulations. Currently the transplantation of pig organs in adequately-immunosuppressed baboons results in graft function for periods of 2–6 months (auxiliary hearts) and 2–3 months (life-supporting kidneys). Pig islets have maintained normoglycemia in diabetic monkeys for >6 months. The remaining immunologic barriers to successful xenotransplantation are discussed, and brief reviews made of (1) the potential risk of the transmission of an infectious microorganism from pig to patient and possibly to the public at large, (2) the potential physiologic incompatibilities between a pig organ and its human counterpart, (3) the major ethical considerations of clinical xenotransplantation, and (4) the possible alternatives that compete with xenotransplantation in the field of organ or cell replacement, such as mechanical devices, tissue engineering, stem cell biology and organogenesis. Finally, the proximity of clinical trials is discussed. Islet xenotransplantation is already at the stage where clinical trials are actively being considered, but the transplantation of pig organs will probably require further genetic modifications to be made to the organ-source pigs to protect their tissues from the coagulation/anticoagulation dysfunction that plays a significant role in pig graft failure after transplantation in primates.Key words: islets, pancreatic, genetic engineering, organogenesis, pig, xenotransplantation     

Genetic transformation of barley microspores using anther bombardment

Bombardment of intact anthers of commercial barley (Hordeum vulgare) varieties resulted in 0.5–1.0% of transformed microspores of which 20–40% continued in androgenic development (0.2% of all bombarded microspores). Using a system based on bombardment of anthers is therefore likely to be more technically efficient than the use of a microspore isolation, transformation and regeneration system. Bombardment of anthers has a number of technical and scientific advantages over existing systems for gene transfer and can be considered as a alternative method to existing methods for genetic transformation in barley.     

Cloning and molecular characterisation of a potato SERK gene transcriptionally induced during initiation of somatic embryogenesis

Somatic embryogenesis offers great potential in plant propagation, long-term germplasm conservation, and as a suitable model system for deciphering early events during embryogenesis. The up-regulation and ectopic expression of a SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) gene has been shown to mark and enhance embryogenic competence in somatic cells of model plant species. We have cloned and characterised a SERK gene (StSERK1) from potato (Solanum tuberosum L.), an important crop plant. Sequence analysis of StSERK1 revealed high levels of similarity to other plant SERKs, as well as a conserved intron/exon structure which is unique to members of the SERK family. Furthermore, StSERK clustered most closely with SERK gene family members such as MtSERK1, CuSERK1, AtSERK1, and DcSERK, implicated in evoking somatic embryogenesis. Monitoring of SERK expression during progression of potato somatic embryogenesis revealed increased StSERK expression during the induction phase. Subsequently, during the embryo transition phases, StSERK expression was unchanged and did not vary among embryo-forming and inhibitory conditions. However, in isolated somatic embryos StSERK expression was again up-regulated. In other plant parts (leaves, true potato seeds, microtubers and flower buds), StSERK showed different levels of expression. Expression analysis suggests that the isolated StSERK could be a functional SERK orthologue. The possible role of SERK as a marker of pluripotency, rather than embryogenesis alone, is discussed.     

Alterations in surface-associated peroxidases during in vitro root development of explants of Linum usitatissimum

Hypocotyl explants of Linum usitatissimum were induced to form roots without an intermediate eallus phase by incubation on a defined medium. Loosely bound and ionically bound surface-associated proteins were extracted from the explants during root development by sequential vacuum infiltration using distilled water and 100 mM calcium chloride solution. The ionically extracted samples generally had higher peroxidase activity than the secreted samples, but both had reached maxima after 28 days culture. In contrast, the secreted samples were more able to oxidise indole-3-acetic acid (IAA) than the ionically-extracted samples. After 14 days culture the peroxidase and IAA-oxidase activities of the two samples were approximately equal, but by 35 days the secreted sample was twice as effective in oxidising IAA as the ionically extracted sample. The results suggest an accumulation of a loosely associated IAA-oxidase/peroxidase on the surfaces of the explants during root growth and development. Five anionic (A₁–A₅) and five cationic (C₁–C₅) isozymes were identified using non-denaturing PAGE. All five anionic isozymes were present throughout the development of roots and became more abundant from 14 days to 35 days culture. In contrast, root development was accompanied by a reduction in the levels of cationic isozymes that are characteristic of hypocotyl tissue. Two cationic isozymes (C₃ and C₄) were exclusively present during the early phases of root development (14 days) and the other three cationic isozymes were present at 14 days, dropped in abundance at 21 days and then recovered to higher levels after 35 days.The possible roles and consequence of these cationic isozymes and the significance of their removal from the explant surface during root development is discussed.Abbreviations NAA -naphthaleneacetic acid - IAA indole-3-acetic acid - TMB tetramethylbenzidine - o-D bar-dianisidine - SYR syringaldazine - MES 2[morpholino]ethane sulfonic acid - BSA Bovine Serum Albumin     

Breeding orange-winged Amazon parrots in captivity

Captive propagation of parrots for the companion bird trade provides a potential means of reducing the economic incentive to capture these birds from the wild. To test whether environmental and social manipulations might stimulate reproduction in captive, wild-caught orange-winged Amazon parrots (Amazona amazonica), we compared reproductive performance in pairs presented with nest boxes (controls) or nest boxes plus additional environmental and social manipulations (enriched group) consisting of misting, fruit supplementation, nest hole restriction, enlarged nest boxes, and pair separation/reunification. In the first breeding trial, in 1990, enriched pairs were more likely to lay eggs (six of seven enriched pairs vs. one of eight control pairs; P < 0.09). When treatments were reversed the following years (e.g., 1990 controls were exposed to enriched conditions in 1991), reproductive performance was not different between the groups (four of seven enriched pairs laid eggs vs. five of seven control pairs), although three pairs in the 1991 enriched group laid eggs which had not laid eggs before. These results are consistent with the idea that while enriched environments may enhance the probability of a first episode of egg laying in captivity, once pairs have laid eggs in captivity, little stimulation beyond that provided by nest box presentation is required to reinitiate egg laying. The environmental and social manipulations of the enriched conditions could be useful in increasing reproductive performance of captive Amazon parrots for the companion bird trade. © 1995 Wiley-Liss, Inc.     

The role of sigma factor RpoH1 in the pH stress response of <Emphasis Type="Italic">Sinorhizobium meliloti</Emphasis>

Background  

Environmental pH stress constitutes a limiting factor for S. meliloti survival and development. The response to acidic pH stress in S. meliloti is versatile and characterized by the differential expression of genes associated with various cellular functions. The purpose of this study was to gain detailed insight into the participation of sigma factors in the complex stress response system of S. meliloti 1021 using pH stress as an effector.     

Physiological roles of taurine in heart and muscle

Taurine (aminoethane sulfonic acid) is an ubiquitous compound, found in very high concentrations in heart and muscle. Although taurine is classified as an amino acid, it does not participate in peptide bond formation. Nonetheless, the amino group of taurine is involved in a number of important conjugation reactions as well as in the scavenging of hypochlorous acid. Because taurine is a fairly inert compound, it is an ideal modulator of basic processes, such as osmotic pressure, cation homeostasis, enzyme activity, receptor regulation, cell development and cell signalling. The present review discusses several physiological functions of taurine. First, the observation that taurine depletion leads to the development of a cardiomyopathy indicates a role for taurine in the maintenance of normal contractile function. Evidence is provided that this function of taurine is mediated by changes in the activity of key Ca²⁺ transporters and the modulation Ca²⁺ sensitivity of the myofibrils. Second, in some species, taurine is an established osmoregulator, however, in mammalian heart the osmoregulatory function of taurine has recently been questioned. Third, taurine functions as an indirect regulator of oxidative stress. Although this action of taurine has been widely discussed, its mechanism of action is unclear. A potential mechanism for the antioxidant activity of taurine is discussed. Fourth, taurine stabilizes membranes through direct interactions with phospholipids. However, its inhibition of the enzyme, phospholipid N-methyltransferase, alters the phosphatidylcholine and phosphatidylethanolamine content of membranes, which in turn affects the function of key proteins within the membrane. Finally, taurine serves as a modulator of protein kinases and phosphatases within the cardiomyocyte. The mechanism of this action has not been studied. Taurine is a chemically simple compound, but it has profound effects on cells. This has led to the suggestion that taurine is an essential or semi-essential nutrient for many mammals.