Genetic and Epigenetic Control of the Proliferation and Differentiation of Mouse Epidermal Melanocytes in Culture

Serum-free culture of epidermal cell suspensions from neonatal skin of mice of strain C57BL/10JHir (B10) showed that α-melanocyte-stimulating hormone (α-MSH) was involved in regulating the differentiation of melanocytes by inducing tyrosinase activity, melanosome formation, and dendritogenesis. Dibutyryl adenosine 3′:5′-cyclic monophosphate (DB-cAMP) similarly induced the differentiation of melanocytes. On the other hand, DBcAMP induced the proliferation of epidermal melanocytes in culture in the presence of keratinocytes. Basic fibroblast growth factor (bFGF) was also shown to stimulate the sustained proliferation of undifferentiated melanoblasts in the presence of DBcAMP and keratinocytes. These results suggest that the proliferation and differentiation of mouse epidermal melanoblasts and melanocytes in culture are regulated by the three factors; namely, cAMP, bFGF, and keratinocyte-derived factors. Moreover, serum-free primary culture of mouse epidermal melanocytes derived from B10 congenic mice, which carry various coat color genes, showed that the coat color genes were involved in regulating the proliferation and differentiation of mouse epidermal melanocytes by controlling the proliferative rate, melanosome formation and maturation, and melanosome distribution.     

Light Actions in the Germination of Cocklebur Seeds: III. EFFECTS OF PRE-TREATMENT TEMPERATURE ON GERMINATION RESPONSES TO FAR-RED LIGHT AND ON DARK GERMINATION IN THE RED LIGHT-REQUIRING UPPER SEEDS

Esashi, Y., Oota, H., Saitoh, H. and Kodama, H. 1985. Lightactions in the germination of cocklebur seeds. III. Effectsof pre-treatment temperature on germination responses to far-redlight and on dark germination in the red light-requiring upperseeds.—J. exp. Bot. 36: 1465-1477. Red light (R) responsiveness in R-requiring upper cocklebur(Xanthium pennsylvanicum Wallr.) seeds changed in differentpatterns during a soaking period at different temperatures.At temperatures above 23°C, the responsiveness increasedand then decreased. At lower temperatures (3–18°C),however, it continued to increase throughout an experimentalperiod. The lower temperatures caused germination in the subsequentdark at 33°C, regained the R responsiveness and acquiredthe dark germinability when subsequently exposed to 8°C,to an extent proportional to the duration of the chilling. Far-red (FR) was inhibitory to germination in an earlier soakingperiod at lower temperatures, but its effect gradually decresed,and finally turned promotive. The negative FR response was repeatedlycontrolled by the following R irradiation. However, the positiveFR response was enhanced by an immediate R irradiation, andFR/R reversibility occurred after the second FR. In contrastto the R responsiveness and dark germinability, the positivegermination response to FR was not induced by soaking at 3°C,in which the growth of the axial tissue as a photoreceptivesite did not occur at all. Similarly, it was not manifestedwhen the seeds soaked at 33°C were subsequently subjectedto 8°C. Key words: Cocklebur seeds, dark germination, far-red light, low temperature, red light, seed germination, Xanthium pennsylvanicum     

Fitness minimization and dynamic instability as a consequence of predator–prey coevolution

We analyse dynamic models of the coevolution of continuous traits that determine the capture rate of a prey species by a predator. The goal of the analysis is to determine conditions when the coevolutionary dynamics will be unstable and will generate population cycles. We use a simplified model of the evolutionary dynamics of quantitative traits in which the rate of change of the mean trait value is proportional to the rate of increase of individual fitness with trait value. Traits that increase ability in the predatory interaction are assumed to have negative effects on another component of fitness. We concentrate on the role of equilibrial fitness minima in producing cycles. In this case, the mean trait of a rapidly evolving species minimizes its fitness and it is chased around this equilibrium by adaptive evolution in the other species. Such cases appear to be most likely if the capture rate of prey by predators is maximal when predator and prey phenotypes match each other. They are possible, but less likely when traits in each species determine a one-dimensional axis of ability related to the interaction. Population dynamics often increase the range of parameter values for which cycles occur, relative to purely evolutionary models, although strong prey self-regulation may stabilize an evolutionarily unstable subsystem.     

NATURE OF THE INHIBITION OF PROTEIN SYNTHESIS BY ETHIONINE AND AMINO ACID UPTAKE IN EARLY SEA URCHIN EMBRYOS

The inhibition of protein synthesis by ethionine reported previously was found to be apparent, and ethionine inhibited only amino acid uptake like other usual amino acids. Even under such strong inhibition of the uptake, the syntheses of protein and DNA remained almost undiminished. The uptake of amino acid mixture by sea urchin embryos in the early cleavage stage was found to be carried out by active transport, since it was temperature-sensitive and was inhibited by 2,4-dinitrophenol. The uptake of an amino acid mixture or of single amino acids, e.g., valine, leucine and phenylalanine, was inhibited nonspecifically by an excess amount of other single amino acids added exogenously. Reflecting the inhibition of amino acid uptake, in vivo incorporation of amino acids into the protein fraction was apparently inhibited by excess amounts of other amino acids. As far as tested, the inhibition seems to be nonspecific and competitive for all amino acid species. The uptakes of leucine and phenylalanine were inhibited mutually by competition, with almost the same Km and Ki.     

CHANGES IN ACTIVITIES OF THYMIDYLATE SYNTHASE AND DIHYDROFOLATE REDUCTASE IN SEA URCHIN EGGS AFTER FERTILIZATION

Thymidylate synthase activity in sea urchin eggs increases just after fertilization and decreases 30 min later. Then, cyclic variation in the activity occurs in association with the cleavage cycle. Dihydrofolate reductase activity in fertilized eggs is almost the same as in unfertilized eggs and shows no marked change within 3 hr after fertilization. Aminopterin, an analogue of dihydrofolate, inhibits dihydrofolate reductase, and arrests cleavage. On incubation in sea water containing aminopterin (20-100μM) from the time of fertilization, the development of Clypeaster and Pseudocentrotus eggs was arrested at the 32–64 cell stage, and that of Anthocidaris eggs was arrested at the morula stage. Dihydrofolate (100μM) counteracts the inhibitory effect of aminopterin on egg cleavage. Thymidine at concentrations above 10μM also prevents inhibition by aminopterin. Other deoxyribonucleosides at concentrations of 10μM to 100μM do not affect inhibition of egg cleavage by aminopterin. Deoxyadenosine at concentrations above 5 mM inhibits egg cleavage, but other deoxyribonucleosides have no effect.     

Germination of cocklebur seed and growth of their axial and cotyledonary tissues in response to C2H4, CO2 and/or O2 under water stress

Abstract. Germination modes of lower seeds of cocklebur (Xanthium pennsylvanicum Wallr.) under different water stresses, prepared with mannitol solution, were examined in relation to gaseous factors. As the concentration of mannitol increased, germination was increasingly inhibited at a mode which was drawn by two straight lines having different slopes and meeting at an angle. One is a sharp line occurring at the lower concentrations of mannitol; the other is a gentle line occurring at higher concentrations of mannitol. The former reflected the growth response of axial tissues to mild water stress, whereas the latter reflected the growth response of cotyledonary tissues to severe water stress. The germination potential of cocklebur seeds increased with increasing temperature. Thus, the seeds were more resistant to water stress at higher than al lower temperatures. This increased germination potential under water stress resulted from the greater growth potential of axial tissues, but not cotyledonary tissues, at higher temperature. Increased O₂ levels improved both the reduced axial and cotyledonary growth under water stress. Carbon dioxide predominantly enhanced axial growth under water stress, whereas C₂H₄ exclusively enhanced cotyledonary growth. Thus, these gases were effective in potentiating germination under water stress. When combined with each other, these gases caused more pronounced growth of the axial and cotyledonary tissues, leading to germination under more severe water stresses. Maximal axial and cotyledonary growth under water stress occurred in the simultaneous presence of CO₂, C₂H₄ and O₂, which allowed the germination at higher mannitol concentrations above 0.6 kmol m^?3 From these results, it was suggested that cocklebur seeds would override water stress by depending upon both the Corresponding axial growth and the C₂H₄-responding cotyledonary growth.     

Rice yield enhancement by elevated CO2 is reduced in cool weather

The projected increase of atmospheric CO₂ concentration ([CO₂]) is expected to increase rice yield, but little is known of the effects of [CO₂] at low temperature, which is the major constraint to growing rice in cool climates. We grew rice under two levels of [CO₂] (ambient and elevated by 200 μmol mol^?1) and two nitrogen (N) fertilization regimes in northern Japan in 2003 (cool weather) and 2004 (warm weather) in the field in a free‐air CO₂ enrichment (FACE) system. Elevated [CO₂] significantly increased grain yield in both years in both N regimes, but the magnitude of the increase differed between years: 6% in 2003 vs. 17% in 2004, with a significant interaction between [CO₂] and year. This difference resulted from responses of spikelet number and ripening percentage to elevated [CO₂]. Enhancement of dry matter production and N uptake at heading by elevated [CO₂] was smaller in 2003 than in 2004, although at maturity there was no difference between years. No significant interaction between N regime and [CO₂] was detected in yield and yield components. The results suggest that yield gain due to elevated [CO₂] can be reduced by low temperature.     

Role of male‐biased dispersal in inbreeding avoidance in the grey‐sided vole (Myodes rufocanus)

Effects of male‐biased dispersal on inbreeding avoidance were investigated in a semi‐natural population of Myodes (formerly Clethrionomys) rufocanus using a large outdoor enclosure (3 ha). Parentage of 918 voles weaned from 215 litters and relatedness of mates were analysed using microsatellite loci, and dispersal distances were obtained from mark–recapture live‐trapping data. Natal and breeding male‐biased dispersal was observed. There remained, however, chances that incestuous mating could occur, because not all males dispersed from their natal site, and 51 matings occurred between relatives (relatedness r > 0). The number of weaned juveniles from inbred litters was significantly smaller than that from non‐inbred litters. Fourteen incestuous matings occurred between close relatives (r ≥ 0.25), most of which were those between non‐littermate maternal half siblings (four cases) and those between paternal half siblings (seven cases). When comparing the observed frequencies to the expected ones generated by combining every oestrous female with a male randomly chosen from her surroundings, the observed values for inbreeding of r ≥ 0.25 were significantly smaller than the expectations, while no difference was observed for inbreeding of 0 < r < 0.25. These results suggest that male‐biased dispersal is partly effective to avoid incestuous mating, but it does not provide complete separation of male and female close relatives. Additional mechanisms such as kin discrimination based on familiarity may work in inbreeding avoidance of the vole.     

Pattern Regulation of the Leg Disc of the Fleshfly, Sarcophaga peregeina

A fate map of the hind leg disc of Sarcophaga peregrina was constructed by examining the adult structures of implanted disc fragments. The locations of presumptive adult structures in the disc were similar to those of fore leg disc of Drosophila and Sarcophaga ruficornis . However, the concentric borderlines of the segments could not be ascertained in the present case.
Pattern regulation of disc fragments was studied by culturing them either in adult females for several days or for 3 days in mature larvae placed on wet condition. Cultured disc fragments regenerated or duplicated as in Drosophila , with some exceptions. For instance, the region with a high density of positional values, the upper medial quarter, of the fore leg disc of Drosophila was not found. A characteristic difference in the rate of regeneration or duplication was observed in the implanted fragments, when cultured in larvae or adult hosts. This variable pattern regulation in larval and adult hosts could be due to different compositions of the hemolymph in which would healing of the implanted disc fragments takes place.     

Sequence Diversity and Linkage Disequilibrium within the Merozoite Surface Protein-1 (Msp-1) Locus of Plasmodium falciparum: A Longitudinal Study in Brazil

ABSTRACT. The merozoite surface protein‐1 (MSP‐1) is a major vaccine candidate for the asexual blood stage of malaria. We examined both the extent of sequence diversity in block 17, the 3′end of Msp‐1 gene coding for a 19‐kDa polypeptide (MSP‐1₁₉) putatively involved in red blood cell binding, and the patterns of linkage disequilibrium between polymorphic sites throughout the Msp‐1 locus. The parasite population sample consisted of Plasmodium falciparum isolates collected between 1985 and 1998 in Rondônia. an area of hypoendemic malaria transmission in the southwestern Brazilian Amazon. Results were summarized as follows. (I) Seven block‐17 sequence variants or haplotypes were found among 130 isolates, including two new haplotypes (novel combinations of previously reported amino acid replacements), here named Brazil‐1 (E‐TSR‐F) and Brazil‐2 (Q‐TSR‐F). (2) As previously shown for other Msp‐1 polymorphisms, frequencies of block‐17 haplotypes displayed significant temporal variation. (3) Extensive linkage disequilibrium was demonstrated between neighboring dimorphic sites within block 17, as well as between polymorphisms at the 5′and 3′ends of Msp‐1 (map distance range: 3.83–4.99 kb). (4) The overall patterns of linkage disequilibrium within Msp‐1 remained stable over a period of nearly one decade, and examples of possible ‘epidemic’ expansion of parasites carrying particular Msp‐1 alleles were found in the 1980s and 1990s. These results are discussed in relation to the population biology of P. falciparum and the development of malaria vaccines based on MSP‐1.