Do phospholipases, key enzymes in sperm physiology, represent therapeutic challenges?

The spermatozoon is one of the most differentiated cells in mammals and its production requires an extremely complex machinery. Subtle but critical molecular changes take place during capacitation, which comprises the last series of maturation steps that naturally occur between the cauda epididymidis where spermatozoa are stored and their ultimate destination inside the oocyte. Phospholipases, by hydrolyzing various phospholipids, have been found to be critical in sperm processes such as 1) the control of flagellum beats, 2) capacitation - the molecular transformations preparing the sperm for fertilization, 3) acrosome reaction and 4) oocyte activation by eliciting calcium oscillations. The emerging important role of phospholipases is also emphasized by the fact that alterations of sperm lipids can lead to infertility. Phospholipases may represent valuable targets to develop anti- and pro-fertility drugs. Results obtained in mice are encouraging, since treatment of sperm with recombinant sPLA(2) of group X, known to be involved in capacitation, improves fertilization in vitro, while co-injection of PLCζ RNA with infertile sperm restores oocyte activation.     

Structure,ecology and physiology of root clusters – a review

Hairy rootlets, aggregated in longitudinal rows to form distinct clusters, are a major part of the root system in some species. These root clusters are almost universal (1600 species) in the family Proteaceae (proteoid roots), with fewer species in another seven families. There may be 10–1000 rootlets per cm length of parent root in 2–7 rows. Proteoid roots may increase the surface area by over 140× and soil volume explored by 300× that per length of an equivalent non-proteoid root. This greatly enhances exudation of carboxylates, phenolics and water, solubilisation of mineral and organic nutrients and uptake of inorganic nutrients, amino acids and water per unit root mass. Root cluster production peaks at soil nutrient levels (P, N, Fe) suboptimal for growth of the rest of the root system, and may cease when shoot mass peaks. As with other root types, root cluster production is controlled by the interplay between external and internal nutrient levels, and mediated by auxin and other hormones to which the process is particularly sensitive. Proteoid roots are concentrated in the humus-rich surface soil horizons, by 800× in Banksia scrub-heath. Compared with an equal mass of the B horizon, the A₁ horizon has much higher levels of N, P, K and Ca in soils where species with proteoid root clusters are prominent, and the concentration of root clusters in that region ensures that uptake is optimal where supply is maximal. Both proteoid and non-proteoid root growth are promoted wherever the humus-rich layer is located in the soil profile, with 4× more proteoid roots per root length in Hakea laurina. Proteoid root production near the soil surface is favoured among hakeas, even in uniform soil, but to a lesser extent, while addition of dilute N or P solutions in split-root system studies promotes non-proteoid, but inhibits proteoid, root production. Local or seasonal applications of water to hakeas initiate non-proteoid, then proteoid, root production, while waterlogging inhibits non-proteoid, but promotes proteoid, root production near the soil surface. A chemical stimulus, probably of bacterial origin, may be associated with root cluster initiation, but most experiments have alternative interpretations. It is possible that the bacterial component of soil pockets rich in organic matter, rather than their nutrient component, could be responsible for the proliferation of proteoid roots there, but much more research on root cluster microbiology is needed.     

Autophagy–physiology and pathophysiology

“Autophagy” is a highly conserved pathway for degradation, by which wasted intracellular macromolecules are delivered to lysosomes, where they are degraded into biologically active monomers such as amino acids that are subsequently re-used to maintain cellular metabolic turnover and homeostasis. Recent genetic studies have shown that mice lacking an autophagy-related gene (Atg5 or Atg7) cannot survive longer than 12 h after birth because of nutrient shortage. Moreover, tissue-specific impairment of autophagy in central nervous system tissue causes massive loss of neurons, resulting in neurodegeneration, while impaired autophagy in liver tissue causes accumulation of wasted organelles, leading to hepatomegaly. Although autophagy generally prevents cell death, our recent study using conditional Atg7-deficient mice in CNS tissue has demonstrated the presence of autophagic neuron death in the hippocampus after neonatal hypoxic/ischemic brain injury. Thus, recent genetic studies have shown that autophagy is involved in various cellular functions. In this review, we introduce physiological and pathophysiological roles of autophagy.     

Cyniclomyces guttulatus (Saccharomycopsis guttulata) — culture,ultrastructure and physiology

Organisms that form an essential extra inner lining of selected areas of the stomach mucosa occur in mice, rats and some other animals. The yeast Cyniclomyces guttulatus (Saccharomycopsis guttulata) was shown in this study to line the stomach of domestic and feral rabbits, guinea pigs, and chinchillas. The layer of yeast cells formed a loose barrier between lumen contents and mucosal surface. A rapid rate of multiplication in the stomach provided yeast cells that blended in with stomach lumen contents, passed throught the gut, and were finally excreted in large numbers in fecal pellets. Ascospore formation occurred during passage through the large intestine. The layer of yeast cells lining the stomach had no evident salubrious nor deleterious effect on the animal. C. guttulatus grew rapidly from stomach contents or single fecal pellets in a new enriched semisolid medium. Growth was good at pH 1 through 8 on the solidified enriched medium. A very unusual characteristic of C. guttulatus is optimal growht at 38° C, and growth at 42° C, with failure to grow below 30° C. TEM demonstrated a very thick, laminated cell wall which had a thick, filamentous external coating. There were mitochondria, polyribosomes, lipid droplets, and an unusually large central nucleus. The developing spore nucleus became extremely electron dense and encapsulated, along with condensed mitochondria, ribosomes, short membrane sections and other organelles, in a dense lamellar covering.     

Centers and peripheries: The development of British physiology, 1870–1914

Conclusions By 1910 the Cambridge University physiology department had become the kernel of British physiology. Between 1909 and 1914 an astonishing number of young and talented scientists passed through the laboratory. The University College department was also a stimulating place of study under the dynamic leadership of Ernest Starling.I have argued that the reasons for this metropolitan axis within British physiology lie with the social structure of late-Victorian and Edwardian higher education. Cambridge, Oxford, and University College London were national institutions attracting students from all over England and Wales. In contrast, the provincial colleges drew their clientele from relatively narrow geographic radii. Generally, also, these institutions were regarded as socially inferior to the longer-established universities.A brief survey of the biographies of some British physiologists demonstrates how physiology, as an occupation, became, over the later decades of the century, socially elite. The scientists who achieved full-time posts in the 1870s generally came from somewhat marginal backgrounds. Foster, like his mentors T. H. Huxley and William Sharpey, came from a non-conformist family. Edward Schäfer was also a dissenter and, like Foster, began his professional career as a general practitioner.Physiologists of the succeeding generation, however, came from wealthy families with established intellectual traditions. John Scott Haldane, nephew of John Burdon Sanderson, was the brother of the politician R. B. Haldane and uncle of the historian A. R. B. Haldane.⁷¹ Joseph Barcroft was one of the most affluent of all physiologists.⁷² His family's wealth derived from linen manufacturing. He attended the Ley's School Cambridge, where his schoolmates included Henry Dale, later Director of the National Institute for Medical Research; F. A. Bainbridge, who eventually became Professor of Physiology at St. Bartholomew's Hospital; and the Cambridge historian J. H. Clapham. A. V. Hill, Professor of Physiology at Manchester and, subsequently, London, married Margaret Keynes, sister of John Maynard Keynes and niece of Sir Walter Langdon Brown, Professor of Physic at Cambridge. Margaret Keynes's younger brother, the surgeon Sir Geoffrey Keynes, married a granddaughter of Charles Darwin; their son Richard Keynes also became a physiologist at Cambridge.These families were part of a new class emerging during the late Victorian period, descendants of the great reforming radicals of the 1830s, who had begun to achieve power through positions in the universities, the professions, and the civil service. Their social prestige rested upon their intellectual expertise. Physiology was an appealing research discipline to these groups because of its clear dissociation from industry and commerce. And because physiology's practical face was medicine, its acceptability was reinforced by professional ties.The nature of the Physiological Society confirms this image of physiology as an elite science. By the turn of the century the Society had taken on some of the characteristics of a dining club. The scientific meetings were generally followed by dinner: if the Society met at Oxford, they were entertained at Burdon Sanderson's college, Magdalen.⁷³ Through a black ball system, unwanted candidates could be excluded. In 1912, when the question of admitting foreigners was discussed, E. H. Starling wrote to Edward Schäfer: the Society has very much in it the nature of a club, and a certain amount of personal knowledge of the candidate is always desirable.⁷⁴.The developing institutional structure of physiology in late Victorian Britain indicates, therefore, that we must look beyond the achievements of individuals and departments to understand why physiology flourished. The discipline became part of a new social order in which the professional middle classes assumed increasing power. These groups valued intellectual skill, especially in the pure scienes, as forces both for self-advancement and for progress within society.     

Growing larger with domestication: a matter of physiology,morphology or allocation?

• Domestication might affect plant size. We investigated whether herbaceous crops are larger than their wild progenitors, and the traits that influence size variation.
• We grew six crop plants and their wild progenitors under common garden conditions. We measured the aboveground biomass gain by individual plants during the vegetative stage. We then tested whether photosynthesis rate, biomass allocation to leaves, leaf size and specific leaf area (SLA) accounted for variations in whole‐plant photosynthesis, and ultimately in aboveground biomass.
• Despite variations among crops, domestication generally increased the aboveground biomass (average effect +1.38, Cohen's d effect size). Domesticated plants invested less in leaves and more in stems than their wild progenitors. Photosynthesis rates remained similar after domestication. Variations in whole‐plant C gains could not be explained by changes in leaf photosynthesis. Leaves were larger after domestication, which provided the main contribution to increases in leaf area per plant and plant‐level C gain, and ultimately to larger aboveground biomass.
• In general, cultivated plants have become larger since domestication. In our six crops, this occurred despite lower investment in leaves, comparable leaf‐level photosynthesis and similar biomass costs of leaf area (i.e. SLA) than their wild progenitors. Increased leaf size was the main driver of increases in aboveground size. Thus, we suggest that large seeds, which are also typical of crops, might produce individuals with larger organs (i.e. leaves) via cascading effects throughout ontogeny. Larger leaves would then scale into larger whole plants, which might partly explain the increases in size that accompanied domestication.

     

Cytochrome c oxidase—structure, function, and physiology of a redox-driven molecular machine

Cytochome c oxidase is the terminal member of the electron transport chains of mitochondria and many bacteria. Providing an efficient mechanism for dioxygen reduction on the one hand, it also acts as a redox-linked proton pump, coupling the free energy of water formation to the generation of a transmembrane electrochemical gradient to eventually drive ATP synthesis. The overall complexity of the mitochondrial enzyme is also reflected by its subunit structure and assembly pathway, whereas the diversity of the bacterial enzymes has fostered the notion of a large family of heme-copper terminal oxidases. Moreover, the successful elucidation of 3-D structures for both the mitochondrial and several bacterial oxidases has greatly helped in designing mutagenesis approaches to study functional aspects in these enzymes. Electronic Publication     

A case of non-scaling in mammalian physiology? Body size, digestive capacity, food intake, and ingesta passage in mammalian herbivores

As gut capacity is assumed to scale linearly to body mass (BM), and dry matter intake (DMI) to metabolic body weight (BM(0.75)), it has been proposed that ingesta mean retention time (MRT) should scale to BM(0.25) in herbivorous mammals. We test these assumptions with the most comprehensive literature data collations (n=74 species for gut capacity, n=93 species for DMI and MRT) to date. For MRT, only data from studies was used during which DMI was also recorded. Gut capacity scaled to BM(1.06). In spite of large differences in feeding regimes, absolute DMI (kg/d) scaled to BM(0.76) across all species tested. Regardless of this allometry inherent in the dataset, there was only a very low allometric scaling of MRT with BM(0.14) across all species. If species were divided according to the morphophysiological design of their digestive tract, there was non-significant scaling of MRT with BM(0.04) in colon fermenters, BM(0.08) in non-ruminant foregut fermenters, BM(0.06) in browsing and BM(0.04) in grazing ruminants. In contrast, MRT significantly scaled to BM(0.24) (CI 0.16-0.33) in the caecum fermenters. The results suggest that below a certain body size, long MRTs cannot be achieved even though coprophagy is performed; this supports the assumption of a potential body size limitation for herbivory on the lower end of the body size range. However, above a 500 g-threshold, there is no indication of a substantial general increase of MRT with BM. We therefore consider ingesta retention in mammalian herbivores an example of a biological, time-dependent variable that can, on an interspecific level, be dissociated from a supposed obligatory allometric scaling by the morphophysiological design of the digestive tract. We propose that very large body size does not automatically imply a digestive advantage, because long MRTs do not seem to be a characteristic of very large species only. A comparison of the relative DMI (g/kg(0.75)) with MRT indicates that, on an interspecific level, higher intakes are correlated to shorter MRTs in caecum, colon and non-ruminant foregut fermenters; in contrast, no significant correlation between relative DMI and MRT is evident in ruminants.     

Confronting physiology: how do infected flies die?

Fruit fly immunology is on the verge of an exciting new path. The fruit fly has served as a strong model for innate immune responses; the field is now expanding to use the fruit fly to study pathogenesis. We argue here that, to understand pathogenesis in the fly, we need to understand pathology - and to understand pathology, we need to confront physiology with molecular tools. When flies are infected with a pathogen, they get sick. We group the events following infection into three categories: innate immune responses (defence mechanisms by which the fly attempts to kill or neutralize the microbe, some of which can themselves cause harm to the fly); microbial virulence (mechanisms by which the microbe evades the immune response); and host pathology (physiologies adversely affected by either the immune response or microbial virulence). We divide this review into sections mirroring these categories. The molecular study of infection in the fruit fly has focused on the first category, has begun to explore the second, and has yet to tap the full potential of the fly regarding the third.     

FSH and bone – important physiology or not?

For many years, osteoporosis in women was equated with estrogen deficiency. The recent articles by Zaidi and colleagues offer a new challenge to the estrogen-deficiency-osteoporosis hypothesis by showing that follicle-stimulating hormone (FSH) stimulates osteoclastic bone resorption perhaps through tumor necrosis factor-alpha (TNF-alpha). These authors, however, neglected to mention bone abnormalities and high testosterone levels that were previously shown in FSH-receptor knockout and other modified mice. It is also possible that they have overemphasized potential relationships of these new data with human bone loss. Despite these fascinating data, the paradigm of FSH causing hypogonadal bone loss is not yet ready to displace the estrogen-deficiency-osteoporosis paradigm, although that model already faces considerable challenge.     

2004 SIVB Congress Symposium Proceeding: Mechanisms of somatic embryogenesis in carrot suspension cultures—Morphology,physiology, biochemistry,and molecular biology

Summary Various aspects of somatic embryogenesis in carrot suspension cultures were reviewed on the basis of results obtained in our laboratory. We have established high-frequency and synchronous somatic embryogenesis systems needed for biochemical and molecular analysis. Using these systems, four phases of somatic embryogenesis were identified. The importance of expression of polarities in these phases, particularly from single cells to embryogenic cell clusters, in determining somatic embryogenesis, is emphasized. At the molecular level, genes expressed during somatic embryogenesis were described, and they were classified into three categories: (1) genes involved in cell division, (2) genes involved in organ formation and (3) genes specific for the process of somatic embryogenesis. From the results obtained, it is concluded that discrete developmental phases in carrot somatic embryogenesis are characterized by distinct biochemical and molecular events, but much remains to be understood.