Cyclic AMP oscillations in suspensions of Dictyostelium discoideum

A model developed previously for signal relay and adaptation in the cellular slime mould Dictyostelium discoideum is shown to account for the observed oscillations of calcium and cyclic AMP in cellular suspensions. A qualitative argument is given which explains how the oscillations arise, and numerical computations show how characteristics such as the period and amplitude of the periodic solutions depend on parameters in the model. Several extensions of the basic model are investigated, including the effect of cell aggregation and the effect of time delays in the activation and adaptation processes. The dynamics of mixed cell populations in which only a small fraction of the cells are capable of autonomous oscillation are also studied.     

Body composition in baboons: Evaluating a morphometric method

The objective of this study was to determine whether noninvasive morphometric measurements of olive baboons (Papio cynocephalus anubis) can reliably predict lean body mass and fat mass in this species. Crown-rump length, triceps circumference, and skinfold measures at the neck, subscapular, suprailiac, and triceps sites were obtained prior to necropsy from 21 clinically normal infant baboons at 18 weeks of age and from 22 clinically normal adolescent baboons at 5 years of age. At necropsy, the lean body mass and body fat mass were measured using gravimetric methods. Pearson's correlations and regression analysis were used to test the relationship between direct measures of lean and fat mass obtained at necropsy with calculated estimates based on morphometric measures obtained prior to death. Our null hypothesis was that the morphometric measures (individually or in combination) were not related to direct measures of fat mass or lean mass. Non-linear and multiple regression estimators, by age and gender, were derived and provided increased predictability. Our results indicate that (1) morphometric measures can accurately predict lean body mass in male and female baboons; (2) morphometric measures used to predict lean body mass change with age; (3) morphometric measures are strongly associated with body fat mass at 18 weeks of age but are not as strongly associated with body fat mass in 5-year-old baboons; (4) triceps circumference provides the best single indicator of lean body mass for both genders and age periods; (5) baboons are like humans in that adolescent females tend to accumulate body fat while males of the same age tend to develop lean mass; and (6) combinations of these morphometric measurements explain between 70% and 100% of the variability and can be used to estimate lean and fat mass in baboons.     

Serotoninergic activity stimulates melanin dispersion within dermal melanophores of newts

Systemic injections of 5-hydroxytryptophan (5-HTP), the precursor to serotonin, stimulates melanin dispersion within dermal melanophores of red-spotted newts (Notophthalmus viridescens). Injections of para-Chlorophenylalanine (PCPA), an inhibitor of serotonin synthesis, inhibited melanin dispersion, and hence darkening of the skin, when newts were transferred to a dark background. The results indicate a role for serotoninergic activity in the background adaptation response in this amphibian.     

Inhibitory role of root hairs on transport within root culture bioreactors

An experimental system was developed to produce root cultures of Hyoscyamus muticus with and without the profuse root hairs. Growth in the presence of 7.6 microM pyrene butyric acid (PBA) and 2.2 mM phosphate virtually eliminated root hairs, whereas growth rate, general morphology and nutrient yields remained unchanged in well-mixed flask culture. These root cultures were used to demonstrate decreased flow resistance in a tubular reactor as a result of root hair removal. To assess the impact on bioreactor performance, hairy and hairless root cultures were grown in a highly characterized 15-L bubble column bioreactor. In the absence of root hairs, the mixing was greatly enhanced; mixing times became shorter for the hairless culture at roughly 100 g (fresh weight)/L. By the end of the 3-week culture period, the mixing time of the hairy culture was 29 times longer than that of the hairless culture. The growth rate of the hairless culture in the bioreactor was as much as 2.4 times greater than growth of the hairy culture under the same conditions. The improved reactor performance was reflected in greater biomass accumulation and respiratory activity. These results show that the root hairs-which facilitate nutrient uptake in a static soil environment-are detrimental to growth in a liquid environment as an effect of their stagnating fluid flow and limiting oxygen availability.     

Hematocrits of free-ranging baboons: variation within and among populations

Hematocrits among free-ranging baboons (Papio hamadryas subsp.), from Awash in Ethiopia and Mikumi in Tanzania, varied by region, sex, age, and season of collection. Tanzanian animals had higher mean values than Ethiopian, and hematocrits were higher in the dry season. We discuss the comparability of field and laboratory data and possible reasons for the observed variation.     

Dispersal in sub-Saharan baboons.

In most mammalian species, males tend to leave their natal group and disperse farther than females, while females tend to be philopatric. Primates generally follow this rule, although long-term studies of a variety of species are revealing an increasing number of exceptions. This paper reviews dispersal patterns in 3 subspecies of savanna baboons (Papio cynocephalus cynocephalus, P. cynocephalus anubis, P. cynocephalus ursinus) which exhibit very similar patterns of social organization. Males usually disperse from the natal group at 8-10 years of age. Female dispersal is rare but well documented. Inbreeding avoidance as well as enhanced mating opportunities are suggested as ultimate causes of dispersal. Several proximate factors implicated in the timing of dispersal events are also reviewed.     

Cyclic oscillations in rat hepatic heme oxygenase and delta-aminolevulinic acid synthetase following intravenous heme administration.

Heme administration in vivo results in the suppression of synthesis of rat hepatic δ-aminolevulinic acid (ALA) synthetase and induction of rat hepatic heme oxygenase. Intravenous heme administration in vivo results in the appearance of cyclic progressively damped oscillations of both hepatic ALA synthetase activity and hepatic heme oxygenase activity. Heme oxygenase induction precedes in time the induction of ALA synthetase. ALA synthetase oscillations are observed in hepatic cell cytosol and mitochondrial fractions as well as in the total homogenate. Cycloheximide pretreatment abolishes both the ALA synthetase and heme oxygenase oscillations, while actinomycin D pretreatment has only a minimal effect on the induction of heme oxygenase. These results suggest that hepatic heme metabolism is closely regulated by rapid changes in the capacity to synthesize and catabolize heme, and the cyclic oscillations following intravenous heme may be a manifestation of the feedback regulation processes involved. This regulatory capacity is dependent on protein synthesis, and the primary site of regulation may be at the translational level on the endoplasmic reticulum.     

Cyclic flow of electrons within PSII in thylakoid membranes

In photosynthesis, the electrons released from PSII are considered to be shared mainly by carbon metabolism and the water-water cycle. We demonstrated previously that some electrons are utilized in a CO2- and O2-independent manner in leaves of wild watermelon [Miyake and Yokota (2000) Plant Cell Physiol: 41: 335]. In the present study, we examined the mechanism of this alternative flow of electrons in thylakoid membranes, isolated from fresh spinach leaves, by simultaneously measuring the quantum yield of PSII and the flux of the linear flow of electrons. In the presence of the protonophore nigericin, which eliminates the pH gradient across thylakoid membranes, the quantum yield and the flux of the linear flow of electrons were directly proportional to one another. The quantum yield at a given linear flux of electrons was much higher in the absence of nigericin than in its presence, indicating that an additional or alternative flow of electrons can occur independently of the linear flow in the absence of nigericin. In the presence of nigericin, the alternative flux of electrons increased with decreasing pH and with increasing reduction of the plastoquinone pool. Cyclic flow of electrons in PSII appears to be the most plausible candidate for the alternative flow of electrons. The flux reached 280 micromol x e(-) (mg Chl)(-1) x h(-1) and was similar to that of the CO2- and O2-independent alternative flow of electrons that we found in leaves of wild watermelon. The cyclic, alternative flow of electrons in PSII provides a possible explanation for the alternative flow of electrons observed in vivo.     

Cyclic Oscillations in Melanin Composition within Hairs of Baboons

The wild‐type agouti‐banding pattern for hair is well characterized in lower mammals such as mice. The switch between eumelanin and pheomelanin in bands in the hair results from the interaction of α‐melanocyte stimulating hormone and agouti signal protein through the melanocortin 1 receptor on melanocytes. However, such banding patterns have not been described to date in higher mammals. We now report such ‘agouti’‐banding patterns that occur in several subspecies of baboons, and characterize those hairs using chemical and immunohistochemical methods. Hair and skin samples were obtained from the dorsa of adult male baboons of different subspecies (Papio cynocephalus hamadryas (PCH) and Papio cynocephalus anubis (PCA)). The hairs were excised with scissors into the gray and the white bands of the PCH subspecies and into the black and the yellow bands of the PCA subspecies, and were analyzed for total melanin, eumelanin, and pheomelanin by spectrophotometric and chemical methods. Hairs in the PCA subspecies oscillate between a eumelanic band (with high melanin content) and a pheomelanic band, while hairs in the PCH subspecies oscillate between a eumelanic band (with low melanin content) and a non‐pigmented band. Those chemical data are consistent with the histological appearance of the hair bulbs stained by the Fontana‐Masson technique. The difference in the melanin content between PCH and PCA subspecies is most likely related to tyrosinase levels, as suggested by the presence of unpigmented muzzle in the PCH subspecies compared with the black muzzle in the PCA subspecies.     

Multiple cyclic nucleotide‐gated channels coordinate calcium oscillations and polar growth of root hairs

Calcium gradients underlie polarization in eukaryotic cells. In plants, a tip‐focused Ca²⁺‐gradient is fundamental for rapid and unidirectional cell expansion during epidermal root hair development. Here we report that three members of the cyclic nucleotide‐gated channel family are required to maintain cytosolic Ca²⁺ oscillations and the normal growth of root hairs. CNGC6, CNGC9 and CNGC14 were expressed in root hairs, with CNGC9 displaying the highest root hair specificity. In individual channel mutants, morphological defects including root hair swelling and branching, as well as bursting, were observed. The developmental phenotypes were amplified in the three cngc double mutant combinations. Finally, cngc6/9/14 triple mutants only developed bulging trichoblasts and could not form normal root hair protrusions because they burst after the transition to the rapid growth phase. Prior to developmental defects, single and double mutants showed increasingly disturbed patterns of Ca²⁺ oscillations. We conclude that CNGC6, CNGC9 and CNGC14 fulfill partially but not fully redundant functions in generating and maintaining tip‐focused Ca²⁺ oscillations, which are fundamental for proper root hair growth and polarity. Furthermore, the results suggest that these calmodulin‐binding and Ca²⁺‐permeable channels organize a robust tip‐focused oscillatory calcium gradient, which is not essential for root hair initiation but is required to control the integrity of the root hair after the transition to the rapid growth phase. Our findings also show that root hairs possess a large ability to compensate calcium‐signaling defects, and add new players to the regulatory network, which coordinates cell wall properties and cell expansion during polar root hair growth.     

Ethnic variation in melanin content and composition in photoexposed and photoprotected human skin

We have examined the quantity and composition of melanin in both photoprotected (volar upper arm) and chronically photoexposed (dorsal forearm) skin from a range of different ethnic skin types including African, Indian, Mexican, Chinese and European. The most lightly pigmented (European, Chinese and Mexican) skin types have approximately half as much epidermal melanin as the most darkly pigmented (African and Indian) skin types. However, the composition of melanin in these lighter skin types is comparatively more enriched with lightly coloured, alkali-soluble melanin components (up to three-fold). Regardless of ethnicity, epidermal melanin content is significantly greater in chronically photoexposed skin than it is in corresponding photoprotected skin (up to two-fold). However, by comparison there is only a modest enrichment of lightly coloured, alkali soluble melanin components in photoprotected skin (up to 1.3-fold). Analysis of melanosomes extracted from the epidermis in these subjects indicates that the proportion of spheroidal melanosomes is low in all skin types examined (<10%). This suggests that in human skin, pheomelanin is a very minor component of epidermal melanin, even in the lightest (European) skin types. Analysis of melanosome size revealed a significant and progressive variation in size with ethnicity: African skin having the largest melanosomes followed in turn by Indian, Mexican, Chinese and European. On the basis of these findings, we propose that variation in skin pigmentation is strongly influenced by both the amount and the composition (or colour) of the melanin in the epidermis. Variation in melanosome size may also play a significant role. However, the data also suggest that in human skin there are subtle differences in the mechanisms associated with the maintenance of constitutive pigmentation and facultative hyperpigmentation, respectively.     

Antioxidant function of fungal melanin.

Polyphenols have been implicated in the virulence and oxidant resistance of Cryptococcus neoformans. Although monomeric polyphenols did not protect against the prooxidant, plumbagin, polymeric dopamine-melanin conferred resistance both to hypochlorite and to permanganate. The physiologic antioxidant capacity conferred by melanin was found to be 21.3 x 10(-15) mole-equivalents per cell, a value which approximates oxidant production by stimulated macrophages.     

Electron transfer properties of melanin.

Melanin synthesized from mushroom tyrosinase and 3,4-dihydroxyphenylalanine has been shown to oxidize NADH and NADPH, reduce ferricyanide, oxidized forms of cytochrome c and dichlorophenolindophenol, and catalyze the coupled oxidation of NADH and reduction of ferricyanide. Kinetic studies involving the determination of initial velocity at various concentrations of substrates and product inhibition measurements have been carried out on the NADH-ferricyanide-melanin reaction. The results are consistent with a ping-pong mechanism in which one product is formed prior to the reaction of melanin with the second substrate involving the reversible oxidation and reduction of melanin during the reaction. It may be concluded that melanin is capable of acting as an electron transfer agent in several reduction-oxidation systems.     

Induction of melanin biosynthesis in Vibrio cholerae.

Vibrio cholerae synthesized the pigment melanin in response to specific physiological conditions that were stressful to the bacterium. Pigmentation was induced when V. cholerae was subjected to hyperosmotic stress in conjunction with elevated growth temperatures (above 30 degrees C). The salt concentration tolerated by V. cholerae was lowered by additional abiotic factors such as acidic starting pH of the growth medium and limitation of organic nutrients. Although the amount of toxin detected in the culture supernatant decreased significantly in response to stressful culture conditions, no correlation between the physiological conditions that induced melanogenesis and expression of OmpU or cholera toxin was detected. Since conditions that induce melanin production in V. cholerae occur in both the aquatic environment and the human host, it is possible that melanogenesis has a specific function with respect to the survival of the bacterium in these habitats.