The influence of glutamic and aminoacetic acids on the excitability of the liverwort Conocephalum conicum

Intracellular microelectrode measurements revealed that a resting potential (RP), an action potential (AP) and a calcium component of AP (named voltage transient, VT) can be influenced by glutamic acid (Glu) and aminoacetic acid (glycine, Gly) in the liverwort Conocephalum conicum. In the continuous presence of 5mM Glu or 5mM Gly, the RP hyperpolarized constantly and the plants became desensitized to the excitatory amino acids (Glu or Gly). Under such circumstances, the amplitudes of APs evoked by stimuli other than Glu or Gly grew, as did their calcium components (VTs). The sudden application of 1-15 mM Glu or Gly to a thallus not yet desensitized resulted in an excitation, i.e. a single AP or AP series. Aspartate (Asp) could not substitute for Glu in any way. Simultaneous action of both amino acids acted synergically to trigger APs. The same phenomenon was observed when glycine solution was enriched with N-methyl-D-aspartic acid (NMDA). Gly-induced APs were totally hindered by 1mM D-amino-5-phosphonopentanoic acid (AP5)--an inhibitor of ionotropic glutamate receptors of the NMDA kind. Glu-induced APs could be totally suppressed by 1mM AP5 as well as by 1mM 6,7-dinitroquinoxaline-2,3-dione (DNQX)--an inhibitor of AMPA/KA receptors. DNQX also completely blocked the calcium component of Glu-evoked APs. After DNQX treatment, the only response to Glu was a membrane potential hyperpolarization (like the Glu response in a desensitized plant). It was concluded that the Glu-induced depolarization and hyperpolarization are separate phenomena. The stimulatory effects of both Glu and Gly on liverwort excitability may be the consequences of an activation of a variety of ionotropic Glu receptor subtypes.     

Role of endogenous zinc in bones of newborn rats

Concentration of abundant elements e.g. calcium as well as of elements present in trace amount e.g. zinc in mandibles of 7, 14 an 28 day old newborn rats were determined by X-ray fluorescence analysis. The measurements were carried out by using a measurement system containing X-ray tube ECLIPSE-III and X-ray and gamma ray detector XR-100T-CdTe (Amptek Inc.). Concentration of calcium and zinc depended on the region of interest on the rat's mandible due to mineralization degree conditioned by its function. Increasing age produced a remarkable increase in Ca content in contrast to Zn content in the bone tissue obtained from 7, 14 and 28 day old newborn rats. The calculated Zn/Ca concentration ratio was the biggest for 7 day old newborns and successively decreased with age indicating the important role of zinc at the beginning of bone ontogenesis.     

The temperature–size rule in a rotifer is determined by the mother and at the egg stage

In most ectotherms, compared with development at low temperatures, development at high temperatures results in the acceleration of maturation, which in turn results in a smaller size (temperature–size rule, TSR). It is not known at which developmental stages this thermal response is determined. We exposed different life stages of the rotifer Lecane inermis to 15, 20, or 25 °C to determine whether the TSR in the F1 generation is governed by the thermal conditions experienced by the mothers (F0 generation) during their development, during egg production, or during the development of the eggs or hatchlings. We found that the adult size was affected by the thermal conditions experienced by the mothers and embryos, but not by the conditions during post-hatching growth. We suggest that the thermal plasticity producing the TSR in rotifers may reflect the joint impacts of a maternal effect and a direct effect of the environment during egg development. The two-point control of the TSR resembles the thermal determination of other biological phenomena, similar to the thermally determined sex determination in ectotherms. Our results contribute not only to better understanding the proximate mechanisms of TSR, but also to comprehending the general biological mechanisms of response to temperature, which is one of the most important ecological factors.     

A comparative analysis of the morphology and evolution of permanent sperm depletion in spiders

Once thought to be energetically cheap and easy to produce, empirical work has shown that sperm is a costly and limited resource for males. In some spider species, there is behavioral evidence that sperm are permanently depleted after a single mating. This extreme degree of mating investment appears to co-occur with other reproductive strategies common to spiders, e.g. genital mutilation and sexual cannibalism. Here we corroborate that sperm depletion in the golden orb-web spider Nephila clavipes is permanent by uncovering its mechanistic basis using light and electron microscopy. In addition, we use a phylogeny-based statistical analysis to test the evolutionary relationships between permanent sperm depletion (PSD) and other reproductive strategies in spiders. Male testes do not produce sperm during adulthood, which is unusual in spiders. Instead, spermatogenesis is nearly synchronous and ends before the maturation molt. Testis size decreases as males approach their maturation molt and reaches its lowest point after sperm is transferred into the male copulatory organs (pedipalps). As a consequence, the amount of sperm available to males for mating is limited to the sperm contained in the pedipalps, and once it is used, males lose their ability to fertilize eggs. Our data suggest that PSD has evolved independently at least three times within web-building spiders and is significantly correlated with the evolution of other mating strategies that limit males to monogamy, including genital mutilation and sexual cannibalism. We conclude that PSD may be an energy-saving adaptation in species where males are limited to monogamy. This could be particularly important in web-building spiders where extreme sexual size dimorphism results in large, sedentary females and small, searching males who rarely feed as adults and are vulnerable to starvation. Future work will explore possible energetic benefits and the evolutionary lability of PSD relative to other mate-limiting reproductive behaviors.     

Female genital system of the folding-trapdoor spider Antrodiaetus unicolor (Hentz, 1842) (Antrodiaetidae, Araneae): ultrastructural study of form and function with notes on reproductive biology of spiders

The genitalia of the female folding-trapdoor spider Antrodiaetus unicolor are characterized by two pairs of spermathecae that are arranged in a single row and connected to the roof of the bursa copulatrix. Each single spermatheca is divided into three main parts: stalk, bowl, and bulb, which are surrounded by the spermathecal gland. The epithelium of the spermathecal gland is underlain by a muscle meshwork and consists of different types of cells partly belonging to glandular cell units (Class 3 gland cells) that extend into pores in the cuticle of the stalk and bowl. Interestingly, the bulb lacks glandular pores and is characterized by a weakly sclerotized cuticle. This peculiarly structured bulb probably plays an important role in the discharge of the sperm mass. It is suggested that by contraction of the muscle layer the sperm mass may be squeezed out, when the bulb invaginates and expands into the spermathecal lumen, pushing the sperm to the uterus lumen. Each glandular unit consists of usually one or two central secretory cells that are for the most part surrounded by a connecting cell that again is surrounded by a canal cell. The canal cell, finally, is separated from the other epithelial cells (intercalary cells) located between the glandular units by several thin sheath cells that form the outer enveloping layer of the unit. The secretions are released through a cuticular duct that originates proximally between the apical part of the connecting cell and the apical microvilli of the secretory cells and runs into a pore of the spermathecal cuticle. The glandular products of the Class 3 gland cells likely contribute to the conditions allowing long-term storage of the spermatozoa in this species. Details regarding the ovary, the uterus internus, and the uterus externus are reported. Most of the secretion that composes the chorion of the egg is produced in the ovary. Glandular cell units observed in the uterus externus differ structurally from those in the spermathecae and likely play a different role. Finally, we briefly discuss our results on the female genitalia of A. unicolor in the light of knowledge about the reproductive biology of spiders.     

A new unusual low molecular weight carbohydrate in the red algal genus <Emphasis Type="Italic">Hypoglossum</Emphasis> (Delesseriaceae,Ceramiales) and its possible function as an osmolyte

The low molecular weight carbohydrates in various species of the red algal genus Hypoglossum (Delesseriaceae, Ceramiales) were analysed using HPLC, ¹H and ¹³C-nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. All specimens contained the heteroside digeneaside which is considered as chemosystematic marker for the Ceramiales. A new HPLC method was developed for the separation and quantification of this compound, and concentrations between 131.6 mmol kg^–1 and 539.6 mmol kg^–1 DW could be measured among the species tested. In addition, during the HPLC analysis another new low molecular weight carbohydrate was detected in two species from The Philippines (H. barbatum) and Western Australia (H . heterocystideum), and its chemical structure elucidated as digalactosylglycerol applying various NMR experiments. The remaining Hypoglossum taxa lack this compound. Although digalactosylglycerol occurred in high concentrations in the range of 221.7 and 438.7 mmol kg^–1 DW in H. barbatum and H . heterocystideum, respectively, it has never been reported for any other algal species before. Therefore, to test the possible physiological function of this unusual carbohydrate as organic osmolyte, H. barbatum was treated with a range of salinities. While the digeneaside content remained almost unchanged, the digalactosylglycerol concentration strongly increased with increasing salinities from 70 mmol kg^–1 DW at 20 psu to 215 mmol kg^–1 DW at 45 psu. In conclusion, while neither published work nor the present study indicate digeneaside to play more than a minor role in osmotic acclimation, the data presented strongly support an osmotic function of digalactosylglyerol.     

Selective expression of a dominant-negative form of peroxisome proliferator-activated receptor in keratinocytes leads to impaired epidermal healing

Many nuclear hormone receptors are involved in the regulation of skin homeostasis. However, their role in the epithelial compartment of the skin in stress situations, such as skin healing, has not been addressed yet. The healing of a skin wound after an injury involves three major cell types: immune cells, which are recruited to the wound bed; dermal fibroblasts; and epidermal and hair follicle keratinocytes. Our previous studies have revealed important but nonredundant roles of PPARalpha and beta/delta in the reparation of the skin after a mechanical injury in the adult mouse. However, the mesenchymal or epithelial cellular compartment in which PPARalpha and beta/delta play a role could not be determined in the null mice used, which have a germ line PPAR gene invalidation. In the present work, the role of PPARalpha was studied in keratinocytes, using transgenic mice that express a PPARalpha mutant with dominant-negative (dn) activity specifically in keratinocytes. This dn PPARalpha lacks the last 13 C terminus amino acids, binds to a PPARalpha agonist, but is unable to release the nuclear receptor corepressor and to recruit the coactivator p300. When selectively expressed in keratinocytes of transgenic mice, dn PPARalphaDelta13 causes a delay in the healing of skin wounds, accompanied by an exacerbated inflammation. This phenotype, which is similar to that observed in PPARalpha null mice, strongly suggests that during skin healing, PPARalpha is required in keratinocytes rather than in other cell types.     

Genetic- or transforming growth factor-beta 1-induced changes in epidermal peroxisome proliferator-activated receptor beta/delta expression dictate wound repair kinetics

Advances in wound care are of great importance in clinical injury management. In this respect, the nuclear receptor peroxisome proliferator-activated receptor (PPAR)beta/delta occupies a unique position at the intersection of diverse inflammatory or anti-inflammatory signals that influence wound repair. This study shows how changes in PPARbeta/delta expression have a profound effect on wound healing. Using two different in vivo models based on topical application of recombinant transforming growth factor (TGF)-beta1 and ablation of the Smad3 gene, we show that prolonged expression and activity of PPARbeta/delta accelerate wound closure. The results reveal a dual role of TGF-beta1 as a chemoattractant of inflammatory cells and repressor of inflammation-induced PPARbeta/delta expression. Also, they provide insight into the so far reported paradoxical effects of the application of exogenous TGF-beta1 at wound sites.