Antioxidant defence mechanisms: From the beginning to the end (of the beginning)

When life first evolved on Earth, there was little oxygen in the atmosphere. Evolution of antioxidant defences must have been closely associated with the evolution of photosynthesis and of O₂-dependent electron transport mechanisms. Studies with mice lacking antioxidant defences confirm the important roles of MnSOD and transferrin in maintaining health, but show that glutathione peroxidase (GPX) and CuZnSOD are not essential for everyday life (at least in mice). Superoxide can be cytotoxic by several mechanisms: one is the formation of hydroxyl radicals. There is good evidence that OH^· formation occurs in vivo. Other important antioxidants may include thioredoxin, and selenoproteins other than GPX. Nitric oxide may be an important antioxidant in the vascular system. Diet-derived antioxidants are important in maintaining human health, but recent studies employing “biomarkers” of oxidative DNA damage are questioning the “antioxidant” roles of β-carotene and ascorbate. An important area of future research will be elucidation of the reasons why levels of steady-state oxidative damage to DNA and lipids vary so much between individuals, and their predictive value for the later development of human disease.     

Gene prediction: the end of the beginning

A report from the conference entitled Genome Based Gene Structure Determination, Hinxton, UK, 1-2 June, 2000, organised by the European Bioinformatics Institute (EBI).     

Octopus senescence: the beginning of the end

Senescence is a normal stage of an octopus's life cycle that often occurs before death. Some of the following symptoms typify it: lack of feeding, retraction of skin around the eyes, uncoordinated movement, increased undirected activity, and white unhealing lesions on the body. There is inter- and intraspecific variability. Senescence is not a disease or a result of disease, although diseases can also be a symptom of it. Both males and females go through a senescent stage before dying-the males after mating, the females while brooding eggs and after the eggs hatch. There are many aspects of octopus senescence that have not yet been studied. This study discusses the ecological implications of senescence.     

Messenger RNA degradation: beginning at the end

The mechanisms responsible for mRNA decay in mammalian cells, and how specific sequence elements accelerate decay, are unknown. Recent work indicates that 'ARE' instability elements recruit the exosome to promote rapid 3'-to-5' degradation of the mRNA.     

Tetracyclines and host defence mechanisms. Doxycyclinepolymethaphosphate sodium complex (DMSC) compared to doxycycline with regard to influence on some host defence mechanisms.

A new doxycycline preparation, doxycycline polymethaphosphate sodium complex (DMSC), was compared to doxycycline in a cross-over study on six volunteers. The serum levels attained were of the same magnitude, but DMSC was shown to influence the serum bactericidal effect to a lesser degree. In vitro investigations of the influence on chemotaxis showed that DMSC even in high concentrations did not interfere with the spontaneous or induced migration to the same extent as doxycycline.     

Prey selection by Asplanchna girodi (Rotifera): the importance of prey defence mechanisms

1. Predator (laboratory-grown Asplanchna girodi and prey (several field-collected non-carnivorous rotifer species) interactions were studied in the laboratory as a function of both predator and prey densities. The clearance rates of A, girodi decreased with increasing prey density. Predator density had no effect on the feeding of A. girodi. 2. Asplanchna girodi selectively fed on Keratella cochlearis. Its clearance rates for K. cochlearis were much higher than those for Polyarthra and Brachionus. Short-spined forms (spine length less than 25 μm) showed a significantly higher susceptibility to predation than either the non-spined or the long-spined forms. 3. Large Asplanchna individuals fed selectively on reproductive females of K. cochlearis, thereby reducing the fecundity of their prey.     

From elicitins to lipid-transfer proteins: a new insight in cell signalling involved in plant defence mechanisms

Elicitins and lipid-transfer proteins are small cysteine-rich lipid-binding proteins secreted by oomycetes and plant cells, respectively, that share some structural and functional properties. In spite of intensive work on their structure and diversity at the protein and genetic levels, the precise biological roles of lipid-transfer proteins remains unclear, although the most recent data suggest a role in somatic embryogenesis, in the formation of protective surface layers and in defence against pathogens. By contrast, elicitins are known elicitors of plant defence, and recent work demonstrating that elicitins and lipid-transfer proteins share the same biological receptors gives a new perspective to understand the role played by lipid binding proteins, mainly the early recognition of intruders in plants.     

Antioxidant mechanisms of the Nereidid Laeonereis acuta (Anelida: Polychaeta) to cope with environmental hydrogen peroxide

Hydrogen peroxide (H(2)O(2)) is a naturally occurring prooxidant molecule, and its effects in the macroinvertebrate infauna were previously observed. The existence of a gradient of antioxidant enzymes activity (catalase [CAT], glutathione peroxidase [GPx], superoxide dismutase [SOD], and glutathione-S-transferase [GST]) and/or oxidative damage along the body of the estuarine polychaeta Laeonereis acuta (Polychaeta, Nereididae) was analyzed after exposure to H(2)O(2). Because this species secretes conspicuous amounts of mucus, its capability in degrading H(2)O(2) was studied. The results suggest that L. acuta deal with the generation of oxidative stress with different strategies along the body. In the posterior region, higher CAT and SOD activities ensure the degradation of inductors of lipid peroxidation such as H(2)O(2) and superoxide anion (O(2)(.-)). The higher GST activity in anterior region aids to conjugate lipid peroxides products. In the middle region, the lack of high CAT, SOD, or GST activities correlates with the higher lipid hydroperoxide levels found after H(2)O(2) exposure. Ten days of exposure to H(2)O(2) also induced oxidative stress (lipid peroxidation and DNA damage) in the whole animal paralleled by a lack of CAT induction. The mucus production contributes substantially to H(2)O(2) degradation, suggesting that bacteria that grow in this secretion provide this capability.     

In the beginning is the end: regulation of poly(A) addition and removal during early development

The addition of poly(A) tails to nearly all mRNAs within the nucleus was reviewed in the July issue of TIBS. Here we shift focus to the fate of poly(A) tails during early development. At specific times during oogenesis and embryogenesis, the poly(A) tails of certain maternal mRNAs are lengthened, while the tails of a number of other mRNAs are removed. The selective poly(A) addition reactions are regulated by a short, U-rich sequence in the 3' untranslated region, while the removal of poly(A) from specific mRNAs is a 'default state', requiring no specific sequence. These regulated changes in poly(A) length are likely to play a major role in translational regulation in the egg and early embryo.     

Planarian regeneration: its end is its beginning

Why does regeneration take place in some animals but not others? Increased understanding of gene function is required to dissect the genetics, cell biology, and physiological aspects that make regeneration possible. An unlikely model animal, the planarian Schmidtea mediterranea, is proving valuable in this endeavor.