Development of Melanocyte Progenitors in Murine Steel Mutant Neural Crest Explants Cultured With Stem Cell Factor,Endothelin-3, or TPA

Stem cell factor (SCF) has been suggested to be indispensable for the development of neural crest cells into melanocytes because Steel mutant mice (i.e., Sl/Sf¹) have no pig-mented hairs. On the other hand, it has been demonstrated that the addition of endothelin 3 (ET-3) or TPA to neural crest cell cultures can induce melanocyte differentiation without addition of extrinsic SCF. In this study, we excluded the influence of intrinsic SCF by using SI/SI mouse embryos to study more precisely the effects of natural cytokines, such as extrinsic soluble SCF or ET-3, or chemical reagents, such as TPA or cholera toxin. We found that SCF is supplied within the wild-type neural crest explants and that ET-3 cannot induce melanocyte differentiation or proliferation without SCF. These results indicate that SCF plays a critical role in survival or G1/S entry of melanocyte progenitors and that SCF initially stimulates their proliferation and then ET-3 accelerates their proliferation and differentiation. TPA has the ability to elicit neural crest cell differentiation into melanocytes without exogenously added SCF but it is not as effective as SCF because many more melanocytes developed in the wild-type neural crest explants cultured with TPA.     

MAGNESIUM REQUIREMENT IN FERTILIZATION PROCESS OF SEA URCHINS

The Mg²⁺ requirement in fertilization was investigated in sea urchins. It was found that when sea urchin eggs were inseminated in sea water free of Mg²⁺, little fertilization took place. Even when spermatozoa pre-treated with dissolved egg-jelly to induce the acrosome reaction, which needs Ca²⁺, were used, the fertilization rate remained quite low in the absence of Mg²⁺. In Strongylo-centrotus intermedius , the lowest concentration of Mg²⁺ required for 50% fertilization was 0.05 mM in the presence of 10 mM Ca²⁺, whereas that of calcium was 3 mM in the presence of 49 mM Mg²⁺. These critical concentrations increased when the concentration of the other ion decreased. Removal of Mg²⁺ or Ca²⁺ or both from the suspending medium had little adverse effect on sperm motility. The elevation of the fertilization membrane was also induced by butyric acid independent of the presence or absence of Mg²⁺ and/or Ca²⁺. These results indicate that Mg²⁺ are required at least in some process(es) between acrosome reaction and fertilization membrane elevation, such as sperm penetration or membrane fusion.     

DISTRIBUTION OF MATURATION-PROMOTING FACTOR IN STARFISH OOCYTE STRATIFIED BY CENTRIFUGATION

In starfish, cytoplasm taken from maturing oocytes is capable of inducing breakdown of the germinal vesicle and subsequent maturation when injected into immature oocytes. The cytoplasmic factor has been designated as "maturation-promoting factor" (MPF). Ooplasm was stratified by centrifugation of maturing oocytes in density-graded Ficoll-seawater, without disrupting the cell. Three strata were distinguished beginning with the centripetal side: oil cap, hyaline layer and yellow layer. MPF activity was shown to be localized in the hyaline layer. Electron microscopic observation revealed that the hyaline layer contains Golgi complexes, many lucent vesicles and multi-vesicular bodies as distinct organelles, but seldom contains such inclusions as the lipid droplets forming the oil cap, mitochondria, yolk and pigment granules contained in the yellow layer. Based on these observations, a possible cytoplasmic component with MPF activity is discussed.     

Ion gradients in xylem exudate and guttation fluid related to tissue ion levels along primary leaves of barley

The concentration of ions in plant cells and tissues is an essential factor in determining physiological function. In the present study, we established that concentration gradients of mobile ions exist in both xylem exudates and tissues within a barley (Hordeum vulgare) primary leaf. For K⁺ and NO₃^?, ion concentrations generally decreased from the leaf base to the tip in both xylem exudates and tissues. Ion gradients were also found for Pi and Cl^? in the xylem. The hydathode strongly absorbed Pi and re‐translocated it to the rest of the plant, whereas Cl^? was extruded. The ion concentration gradients developed early during leaf growth, increased as the tissue aged and remained under both high and low transpiration conditions. Measurement of the expression profiles of Pi, K⁺ and NO₃^? transporters along the longitudinal axis of the leaf revealed that some transporters are more expressed at the hydathode, but for most transporters, there was no significant variation along the leaf. The mechanisms by which longitudinal ion gradients develop in leaves and their physiological functions are discussed.     

Breakdown of distyly and pin‐monomorphism in Psychotria carthagenensis Jacq. (Rubiaceae)

Rubiaceae contains the largest number of distylous species in the Angiosperms, but the evolution and control of distyly is poorly understood in this group. Atypical distylous populations and species have been described in this family and associated with disturbance, pollination failure and impaired reproductive success. Some of these atypical taxa belong to Psychotria, the largest genus in the family. In the present study, we investigate the pollination and breeding biology of Psychotria carthagenensis Jacq., a widely distributed species that has been described as typically distylous. Fieldwork was carried out mainly at the Panga Ecological Station, in Uberlândia, MG, Brazil. We carried out phenological observations, floral biology studies and hand pollination experiments within the Panga Ecological Station population. We complemented these data with herbarium and field surveys from elsewhere in Brazil. The studied population bloomed at the beginning of the rains (September–December). The main pollinators were Bombus and small Halictidae bees. The Panga Ecological Station population presented pin‐monomorphism with only two thrum individuals in more than 100 flowering individuals surveyed. Hand pollinations at the Panga Ecological Station showed self‐compatibility and intramorph compatibility. Typical distyly and isoplethy were found in other areas and both morphs appeared in herbarium material. However, pin‐monomorphism was also observed elsewhere in Brazil. Typical distyly, pin‐monomorphism and homostyly observed concurrently in Brazilian populations of P. carthagenensis indicate that alternative reproductive strategies, probably favoring selfing, appear to have developed independently in this species.     

Phylogenetic analysis of the Brazilian microendemic Paepalanthus subgenus Xeractis (Eriocaulaceae) inferred from morphology

Paepalanthus subgenus Xeractis (Eriocaulaceae) comprises 28 recognized species endemic to the Espinhaço Range, in Minas Gerais state, Brazil. Most species of the subgenus are restricted to small localities and critically endangered, but still in need of systematic study. The monophyly of the subgenus has already been tested, but only with a few species. Our study presents the first phylogenetic hypothesis within the group, based on morphology. A maximum parsimony analysis was conducted on a matrix of 30 characters for 30 terminal taxa, including all species of the subgenus and two outgroups. The biogeographical hypotheses for the subgenus were inferred based on dispersal–vicariance analysis (DIVA). The analysis provided one most‐parsimonious hypothesis that supports most of the latest published subdivisions (sections and series). However, some conflicts remain concerning the position of a few species and the relationships between sections. The distribution and origin(s) of microendemism are also discussed, providing the ground for conservation strategies to be developed in the region. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 167 , 137–152.     

A phylogenetic analysis of the genus Eunice (Eunicidae, polychaete, Annelida)

Species of Eunice are distributed worldwide, inhabiting soft and hard marine bottoms. Some of these species play significant roles in coral reef communities and others are commercially important. Eunice is the largest and most poorly defined genus in Eunicidae. It has traditionally been subdivided in taxonomically informal groups based on the colour and dentition of subacicular hooks, and branchial distribution. The monophyly of Eunice and of its informal subgroups is tested here using cladistic analyses of 24 ingroup species based on morphological data. In the phylogenetic hypothesis resulting from the present analyses Eunice and its subgroups are paraphyletic; the genus may be divided in at least two monophyletic groups, Eunice s.s. and Leodice , but several species do not fall inside these two groups. Most of the traditional characters used in the taxonomy of Eunice are homoplasies; however, characters used for the first time in this study, such as certain jaw characters and characters derived from a close examination of chaetal variation along the body, are promising sources of phylogenetic signal.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 150 , 413–434.     

Comparing assemblages of Asteraceae and their insect herbivores under different land‐use regimens

Accelerated tropical landscape changes occurring over recent decades have produced environmental mosaics comprising remaining isolated green areas and mixed land‐use types. Our objective was to study the effects of alterations in the natural landscape on the species composition and structure of assemblages of Asteraceae and their endophagous insects through comparisons between cerrado (savanna), pastures and Eucalyptus stands. We first investigated whether similarities between assemblages of Asteraceae and their insects varied among land uses or localities. Secondly, we asked whether assemblages of Eucalyptus stands and pastures are subsets of those within the cerrado. We sampled within randomly deployed transects in 15 areas. Land use was found to be an important factor in determining plant composition similarity; however, locality did not exert any significant influence. Pastures were less similar to one another, suggesting high beta diversity. Similarities among insect assemblages were correlated with plant assemblage composition, but not with land use or locality. Species of Tephritidae were distributed along localities independently of land use. High beta diversity in Asteraceae assemblages among cerrados and pastures was supported by nestedness analysis. Plant assemblages in Eucalyptus stands were subsets of cerrado, but pasture assemblages were only partial subsets. A higher degree of nestedness in insect assemblages than in plant assemblages indicated lower beta diversity within these herbivores. Our data indicate that many herbivores are specialized on widely distributed plant genera. Conservation of Asteraceae species and their flower head insects depends not only on maintenance of landscape fragments but also on the correct matching of management form and land use. Such management may contribute to reducing isolation of plant and insect species by increasing the connectivity of remaining cerrado tracts, allowing population maintenance even at low abundances.     

INDUCTION OF OOCYTE MATURATION BY DISULFIDE-REDUCING AGENT IN THE SEA CUCUMBER, STICHOPUS JAPONICUS

1-Methyladenine (1-MeAde) is known to be a natural inducer of starfish oocyte maturation. Disulfide-reducing agents such as dithiothreitol (DTT) and 2, 3-dimercapto-1-propanol (BAL) are known to mimic the action of 1-MeAde in inducing starfish oocyte maturation. Although 1-MeAde failed to induce oocyte maturation in sea cucumbers, breakdown of germinal vesicles and subsequent meiotic behaviour of chromosomes were induced by the treatment with DTT in the pronase-treated oocytes of the sea cucumber, Stichopus japonicus. These findings suggest that reduction of disulfide bonds plays an important role in triggering oocyte maturation in some marine forms such as echinoderms.