PERIZONIUM AND INITIAL VALVE FORMATION IN THE DIATOM NAVICULA CUSPIDATA (BACILLARIOPHYCEAE)1

This paper describes the perizonium and initial valve formation in Navicula cuspidata Kütz., based on light microscope (LM) and scanning electron microscope (SEM) observations. The perizonium consists of concentric over-lapping bands, laid down sequentially at the tips of the expanding biconical auxospore during its elongation. The central perizonial band has fimbriate edges and is considerably more rigid than the more distal bands. During auxospore elongation and the band secretion, the chloroplasts continuously oscillate between the two ends of the cell; this oscillation ceases once the elongation is complete. The initial valves, formed within the perizonium, are molded into the basically biconical shape of the perizonium except for a central flattening of each valve face. In contrast to the raphes in gametangial and vegetative valves which are surrounded by a smooth axial area, the raphes in initial valves lie within a raised ridge running along the apical axis of the valve. The regular pattern of apically oriented ridges on the outer surface of vegetative valves is also lacking on initial valves. Comparison of pore–pore spacing within striae of gametangial valves, initial values and post-initial valves (first division and vegetative cells) reveals that the pore–pore distance within striae is conserved at all sexual stages. However, the distance between striae is considerably larger in initial valves than in gametangial and post-initial valves. Vegetative interstriae spacing as well as the planar morphology of the valve face is regained at the first division of the initial cell. This suggests that the spacing between striae is dependent on the sexual stage of the cell during valve formation (i.e. not directly dependent on the cell size) and can be altered independently of the pore–pore spacing.     

Selected contribution: Bone adaptation with aging and long-term caloric restriction in Fischer 344 x Brown-Norway F1-hybrid rats.

Rodents are commonly used as models for human aging because of their relatively short life span, the ease of obtaining age-specific tissue samples, and lower cost. However, age-associated disease may confound inbred animal studies. For example, numerous physiologically significant lesions, such as chronic nephropathy, are more common in aged Fischer 344 (F344) rats than in other strains (Bronson RT, Genetic Effects of Aging, 1990). Conversely, F344 x Brown-Norway F1-hybrid (F344BN) rats, developed by the National Institute on Aging for aging research, live considerably longer and have fewer pathologies at any given age vs. inbred strains (Lipman RD, Chrisp CE, Hazzard DG, and Bronson RT, J Gerontol A Biol Sci Med Sci 51: 54-59, 1996). To our knowledge, there are no data regarding the effect of age on bone geometry and mechanics in this strain of rat. Furthermore, caloric restriction (CR) extends the mean and maximal life span of animals and significantly reduces age-associated disease but may have adverse consequences for bone growth and mechanics. Thus we investigated the effects of age and CR on bone geometry and mechanics in the axial and appendicular skeleton of F344 Brown-Norway rats. Ad libitum fed rats were assessed at 8 mo (young adult; n = 6), 28 mo (late middle age; n = 5), and 36 mo (senescence; n = 6). CR rats were assessed at 28 mo (n = 6). Tibiae and the sixth lumbar vertebrae (L6) were dissected, scanned (micro-computed tomography) to determine geometry, and tested mechanically. From 8 to 36 mo, there were no significant changes in L6 geometry, and only the cross-sectional moment of inertia changed (increased) with the tibia. CR-induced body mass reductions accounted for changes in L6 load at proportional limit, maximal load, and stiffness (structural properties), but altered tibial structural properties were independent of body mass. In tibiae, geometric changes dominated alterations in structural properties. Those data demonstrated that, whereas aging in ad libitum-fed animals induced minor changes in bone mechanics, axial and appendicular bones were adversely influenced by CR in late-middle-aged animals in different manners.     

Chorusing Behaviour,a Density-dependent Alternative Mating Strategy in Male Common Toads (Bufo bufo)

Male chorusing behaviour was studied in a population of common toads (Bufo bufo) on the island of Öland south Sweden, and the functional role of male advertisement calling in this species was experimentally examined. Calling males were larger and heavier than non-calling males (t = 2.41, p < 0.025 and t = 2.36, p < 0.025, respectively). However, small males were also found to call. This indicates that large males persisted in calling for longer and/or called more often. The proportion of calling males decreased as population size increased during the breeding season, indicating that calling is a low density strategy. Females responded more readily to calls than males. There were insufficient data to determine if the dominant frequencies of advertisement calls were inversely correlated with male body size, however, this relationship was found for the similar release calls. Females were found not to discriminate between high and low frequency calls, but when given a choice between two calls of different sound pressure levels (SPL), females were attracted to the louder calls. Thus, the function of chorusing is to advertise the position of males to mate-seeking females when the population density is low.     

Nearest-neighbor and next-nearest-neighbor effects in the proton NMR spectra of the oligoribonucleotides ApGpX and CpApX

The variable-temperature proton nmr spectra of the oligoribonucleotides in the series CpApX and the series ApGpX, X = A, G, C, U, together with the parent dimers CpA and ApG have been measured. A complete analysis of all the nonexchangeable base proton resonances and ribose H-1′ proton resonances was made. The presence of trends in the shielding abilities of the various bases at both the nearest-neighbor and next-nearest-neighbor positions were identified. The observed shieldings could be used to predict the chemical shifts of protons in related systems. Based on the empirical results from ribodinucleoside monophosphates, the temperature-dependent behavior of the J_1′2′ coupling constants of the triribonucleotides suggested that the compounds in the CpApX series stacked from the 5′-end to the 3′-end, while those in the ApGpX series stacked from the 3′-end to the 5′-end.     

The role of transferrin and citrate in cellular uptake of aluminium

Summary The ability of human erythroleukaemia K562 cells to take up aluminium from Al-transferrin and Al-citrate has been examined. Uptake from Al-transferrin was dose-dependent over the range 68–544 ng/ml of aluminium, and increased over a 12-day period. In contrast, uptake from Al-citrate was low even at an aluminium concentration of 6800 ng/ml and did not increase over time. Neither form of aluminium greatly affected cell growth. It is concluded that Al-transferrin, rather than Al-citrate, is the physiologically relevant form of this metal with respect to cellular uptake, but that any metabolic abnormalities induced by aluminium do not affect proliferation of this cell line.     

Acentrosomal spindle assembly and maintenance in Caenorhabditis elegans oocytes requires a kinesin-12 nonmotor microtubule interaction domain

During the meiotic divisions in oocytes, microtubules are sorted and organized by motor proteins to generate a bipolar spindle in the absence of centrosomes. In most organisms, kinesin-5 family members crosslink and slide microtubules to generate outward force that promotes acentrosomal spindle bipolarity. However, the mechanistic basis for how other kinesin families act on acentrosomal spindles has not been explored. We investigated this question in Caenorhabditis elegans oocytes, where kinesin-5 is not required to generate outward force and the kinesin-12 family motor KLP-18 instead performs this function. Here we use a combination of in vitro biochemical assays and in vivo mutant analysis to provide insight into the mechanism by which KLP-18 promotes acentrosomal spindle assembly. We identify a microtubule binding site on the C-terminal stalk of KLP-18 and demonstrate that a direct interaction between the KLP-18 stalk and its adaptor protein MESP-1 activates nonmotor microtubule binding. We also provide evidence that this C-terminal domain is required for KLP-18 activity during spindle assembly and show that KLP-18 is continuously required to maintain spindle bipolarity. This study thus provides new insight into the construction and maintenance of the oocyte acentrosomal spindle as well as into kinesin-12 mechanism and regulation.     

Inositol phospholipids are probably not the source of arachidonic acid for eicosanoid synthesis in astrocytes

In astrocyte-enriched cultures of the rat cerebral cortex the Ca2+ ionophore A23187 provoked the breakdown of inositol phospholipids, the liberation of arachidonic acid and the release of prostaglandins E2, F2 alpha, I2 and thromboxane A2. However, agonists for receptors also coupled to inositol phospholipid metabolism in these cells failed to produce an increase in the release of both arachidonic acid and eicosanoids. Results suggest that the A23187-stimulated release of arachidonic acid and eicosanoids is caused by a phospholipase A2-mediated attack on lipids other than the inositol phospholipids. Moreover, receptors linked to inositol lipid turnover are not involved in the control of eicosanoid release from astrocytes.