Cellular mechanisms of stimulation of bud production in Hydra by low levels of inorganic lead compounds

Summary Treatment of Hydra with subtoxic levels of inorganic lead compounds (lead nitrate and lead chloride) for periods ranging from 5 min to one hour causes a temporary increase in bud production as compared to untreated control animals. This effect can be inhibited by the addition of large amounts of calcium chloride to the culture medium.The increased rate of budding is preceded by a dramatic increase in the number of nerve cells per animal, which is first observed within six hours after lead treatment. This appears to be the result of an increased rate of mitosis in the undifferentiated interstitial cells and their subsequent differentiation into nerve cells. The total number of cells per animal also increases after exposure to lead compounds, suggesting that lead may act as a general mitotic stimulator of all dividing cell types in Hydra.This investigation was supported by the National Science Foundation, Grant GB-27395     

Monoamine concentrations in Hydra magnipapillata

Several monoamines and related metabolites were quantified in Hydra magnipapillata using a three dimension HPLC system with multiple coulometric electrochemical detectors. Serotonin (5HT), N-methylserotonin (N-MET) and dopamine were detected, being reported in a coelenterate for the first time. It is suggested that monoamine levels were associated with the interstitial cell lineage. 5HT and N-MET were more concentrated in the body column where nematoblasts and nematocytes develop than in the tentacles and hypostome. It is concluded that the main indoleamine in Hydra is not 5HT but N-MET and a new metabolic pathway in Hydra is suggested: tryptophan-5HT-N-MET.     

The differentiation of cytoskeletal structures in nematocytes of Hydra

Nematocytes of hydra feature a complex cytoskeleton consisting mainly of several bundles of actin filaments and a basket-like structure formed by microtubules. The aim of this study was to establish the sequence of appearance of cytoskeletal elements during nematocyte development using immuno-fluorescence and electron microscopical techniques. Our results are a first step in trying to understand developmental hierarchies and mechanisms which govern the synthesis and assembly of the cytoskeleton in nematocytes. The finger-shaped rods around the apex of the capsule are the first detectable elements of the cytoskeleton. Microtubules of the basket structure then follow and later, the actin filaments of microvilli which support the cnidocil. The actin filaments, however, do not show the highly ordered bundling pattern characteristic of filaments in functional nematocytes.     

The general occurrence of intramitochondrial crystals in Hydra cells

Summary Intramitochondrial crystals are found in normal Hydra as well as in animals undergoing various conditions (budding, regenerating, eserinetreated, and sexual). They appear in all regions of the animal, but seem to be more prevalent at or near the extremities: hypostome, tentacles and basal disk. They are found in all of the seven basic cell types: interstitial, cnidocyte, nerve, epithelio-muscular, gland, mucous and digestive cells. The chemical nature of the intramitochondrial crystals is unknown and their significance remains speculative.This investigation was supported by the National Science Foundation, Grant Number Gb-27395     

Role of epithelial cells and programmed cell death in Hydra spermatogenesis

Spermatogenesis in higher animals is a tightly regulated process, in which survival and death of sperm precursor cells depends on the presence of somatic cells in gonads. In the basal metazoan Hydra spermatogenesis takes place in anatomically simple testes and in the absence of accessory structures. Hydra sperm precursors are derived from interstitial stem cells. Here we show that large numbers of sperm precursors in testes of Hydra vulgaris undergo programmed cell death (apoptosis) and that ectodermal epithelial cells phagocytose the apoptotic sperm precursors. This is surprising since so far no evidence has been reported that epithelial cells are directly involved in germ cell differentiation in Hydra. We propose that, similar to Sertoli cells in mammals, in Hydra epithelial cells support and perhaps even control spermatogenesis.     

The Hydra viridis/Chlorella symbiosis. Growth and sexual differentiation in polyps without symbionts

To investigate interactions between the basal metazoan Hydra viridis and its symbiotic Chlorella algae, we generated aposymbiotic hydra lacking algae and compared them to symbiotic ones with regard to growth and sexual differentiation. Under standard feeding conditions aposymbiotic polyps proliferated similarly to symbiotic polyps. Under moderate and low feeding conditions asexual growth was reduced in polyps lacking algae, indicating that the symbionts supply nutrients to their hosts. In addition, the Chlorella symbionts had a strong influence on the sexual reproduction of Hydra viridis: in most cases female gonads were produced only when symbiotic algae were present. Spermatogenesis proceeded similarly in symbiotic and aposymbiotic polyps. Since during oogenesis symbionts are actively transferred from endodermal epithelial cells to the ectodermal oocytes, this oogenesis promoting role could indicate that the symbionts are critically involved in the control of sexual differentiation in green hydra.     

Histological and ultrastructural studies of the basal disk of Hydra

Summary The gastrodermis and mesoglea of the basal disk of Hydra were investigated to conclude a three-part series of papers. The gastrodermis is composed of digestive cells (most predominant cell type), mucous and nerve cells (both immature and fully differentiated). The principal function of the digestive cells appears to be storage of protein, lipid and glycogen reserves which are utilized by neighboring cells. Mucous cells apparently use some of the reserves to synthesize their secretions which lubricate cells and prevent cell damage during egestion of waste through the aboral pore. The function of the gastrodermal nerve cells is uncertain.The mesoglea of the basal disk, contains the same structural components as seen in other regions of the polyp. It is reasonable to assume that it maintains the same function of cell adhesion and migration. As the mesoglea converges on the aboral pore, it loses its structural integrity and cells are sloughed off the column.This investigation was supported by The National Science Foundation, Grant Number GB-27395.     

Histological and ultrastructural studies of the basal disk of Hydra

Summary The glandulomuscular cells of Hydra are located exclusively in the basal disk. They are derived from epithelio-muscular cells which have been forced proximally. Light and electron microscopical studies show that prior to their destruction and elimination, the transformed epithelio-muscular cells (i.e. the glandulomuscular cells) undergo certain striking morphological and physiological changes. Golgi complexes and elements of rough E. R. increase remarkably in activity, and individually or jointly produce at least six types of morphologically different droplets. One additional type of droplet is thought to originate from neighboring digestive cells. Although the chemical nature of the individual droplets is uncertain, it is known that some are Alcian blue and PAS positive and contain hyaluronic acid. These evidences suggest the presence of an acid mucopolysaccharide material, the adhesive agent which attaches the animal to a substrate. The myonemes contain thick (200 Å in diameter) and thin (60 Å in diameter) filaments as in epithelio-muscular cells. There are also filaments of intermediate sizes and large fibers (770 Å in diameter). The myonemes are oriented radially with respect to the aboral pore and therefore in addition to contributing to the contraction and relaxation of the body column, they apparently regulate the opening and closing of the aboral pore. Although there is no evidence to substantiate the mechanism for transformation of epithelio-muscular cells to glandulomuscular cells as well as cell death of the latter cell types, these problems are discussed briefly.This investigation was supported by The National Science Foundation, Grant Number GB-27395.With the technical assistance of Linda M. Bookman.     

Tumour-promoting phorbol esters rapidly inhibit bud formation in hydra

Summary The effects of tumour promoters and carcinogens on bud formation were investigated in an attempt to clarify the primary process of bud formation in hydra. Treatment with 1.0ng/ml 12-O-tetradecanoylphorbol-13-acetate (TPA), phorbol-12,13-didecanoate (PDD) or mezerein added immediately after feeding rapidly and completely inhibited the formation of new buds in Hydra japonica. Treatment with TPA 3–6 h after feeding also suppressed bud formation 24 h later, but suppressed buds appeared 48 h later. Buds suppressed by TPA also formed in the presence of a diluted homogenate of hydra and during starvation. Carcinogens, such as benzo(a)pyrene and 20-methylcholanthrene, did not have an inhibitory effect on bud formation within 2 days. The tumour promoters and carcinogens used in this experiment did not inhibit the regeneration of tentacles. These results indicate that tumour-promoting phorbol esters, but not carcinogens, rapidly suppress the process by which the formation of buds is initiated by hydra, and the effects of these esters depend on the timing of treatment after feeding.     

The role of nerve cell density in the regulation of bud production in hydra

Summary The role of nerve cell density in the regulation of bud production in hydra was examined. Animals with different rates of bud production were produced by altering the temperature, population density and illumination of their cultures. When the distribution of cell types was examined in animals with different rates of bud production, the density of nerve cells in those animals was found to be correlated with their rate of bud production. Transfer of animals from one environment to another resulted in immediate changes in the rate of differentiation of large interstitial cells into nerve cells. This suggests that the density of nerve cells may play a role in regulating the rate of bud production in hydra.     

Foot differentiation and genomic plasticity in Hydra: lessons from the PPOD gene family

In Hydra, developmental processes are permanently active to maintain a simple body plan consisting of a two-layered, radially symmetrical tube with two differentiated structures, head and foot. Foot formation is a dynamic process and includes terminal differentiation of gastric epithelial cells into mucous secreting basal disc cells. A well-established marker for this highly specialized cell type is a locally expressed peroxidase (Hoffmeister et al. 1985). Based on the foot-specific peroxidase activity, the gene PPOD1 has been identified (Hoffmeister-Ullerich et al. 2002). Unexpectedly, this approach led to the identification of a second gene, PPOD2, with high sequence similarity to PPOD1 but a strikingly different expression pattern. Here, we characterize PPOD2 in more detail and show that both genes, PPOD1 and PPOD2, are members of a gene family with differential complexity and expression patterns in different Hydra species. At the genomic level, differences in gene number and structure within the PPOD gene family, even among closely related species, support a recently proposed phylogeny of the genus Hydra and point to unexpected genomic plasticity within closely related species of this ancient metazoan taxon. Electronic supplementary material Supplementary material is available in the online version of this article at     

Immunohistochemical evidence for the existence of novel mammalian neuropeptides related to the Hydra GLW-amide neuropeptide family

The GLW-amide family is a neuropeptide family found in cnidarian species and is characterized by the C-terminal amino acid sequence -Gly-Leu-Trp-NH₂. To detect mammalian peptides structurally related to the GLW-amide family, we examined rat brain by immunohistochemistry with an anti-GLW-amide antibody. GLW-amide-like immunoreactivity (GLW-amide-LI) was observed in thin varicose fibers in some regions of the brain. Most neurons showing GLW-amide-LI were observed in the laterodorsal tegmental nucleus, pedunculopontine tegmental nucleus, and trigeminal/spinal ganglia. These results strongly suggest that the rat nervous system contains as yet unidentified GLW-amide-like peptides, and that GLW-amide-LI in the brain is a good marker for ascending projections from mesopontine cholinergic neurons. This work was supported by grants from the Ministry of Education, Sports, and Culture, Japan.     

Self/nonself recognition in Cnidaria: contact to allogeneic tissue does not result in elimination of nonself cells in Hydra vulgaris

Although Cnidaria have no specialised immune cells, some colonial forms possess a genetic system to discriminate between self and nonself. Allorecognition is thought to protect them from fusion with genetically different individuals and to prevent germ line parasitism. Surprisingly, when grafting tissue of two species of the solitary freshwater polyp Hydra, we found within the contact zone phagocytozing epithelial cells which selectively eliminated cells from the other species (Bosch and David, 1986). This led us to speculate that Hydra, which never undergoes "natural transplantation", can differentiate between self and nonself (Bosch and David, 1986). In a previous paper (Kuznetsov et al., 2002) we described that cells which accumulate in the contact region of these interspecies grafts are apoptotic and that apoptosis is induced by impaired cell matrix contact. Thus, observations in such interspecies grafts did not give hints concerning the presence of a discriminative allorecognition system. To clarify whether this fundamental aspect of immunity is present in these phylogenetically old animals, we examined epithelial interactions between different strains of Hydra vulgaris. Here, we show that contact to allogeneic tissue does not evoke any response in terms of phagocytosis and elimination of allogeneic cells. We, therefore, question Hydra's ability to discriminate between self and nonself and propose that, in contrast to colonial cnidarians, the solitary polyp Hydra has either lost or substantially reduced this ability.     

Pulses of ammonia and methylamine induce down-regulation of nematocyte and nerve cell populations in Hydrozoa (Hydra; Hydractinia)

Summary Hydrozoa replace used-up nematocytes (cnidocytes) by proliferation and differentiation from interstitial stem cells (i cells). Repeated pulsed exposure ofHydra to elevated levels of unprotonated ammonia leads to successive loss of the various types of nematocytes: first of the stenoteles, then of the isorhizas and finally of the desmonemes. The loss is due to deficits in supply; the number of nematoblasts and differentiating intermediates is reduced. In the hydroidHydractinia the main process leading to numerical reduction was observed in vivo: mature nematocytes as well as precursors emigrate from their place of origin into the gastrovascular channels where they are removed by phagocytosis. This is a regular means by which these animals down-regulate an induced surplus of nematocytes. With lower effectiveness, pulses of methylamine, trimethylamine and glutamine also induce elimination of the nematocyte lineages. In the long term the population of nerve cells, which are permanently but slowly renewed from interstitial neuroblasts, decreases, too. After 2 months of daily repeated treatment the density of the Arg-Phe-amide-positive nerve cells was reduced to 50% of its normal level. Thus, ammonia induces down-regulation of all interstitial cell lineages. The temporal sequence of the ammonia-induced loss reflects the diverse rates with which the various i cell descendants normally are renewed.     

Interaction between the effects of light pulses of different chromatic content on Hydra attenuata and H. magnipapillata

The pattern of Hydra periodic shortening-elongation behaviour can be modified by photic stimulation. The response time between the end of a pulse stimulus and the beginning of the next body shortening event is a function of: 1) the polarity of the pulse; 2) the intensity of the pulse, 3) the phase of application of the pulse during a shortening-elongation period, 4) the wavelength of the pulse, 5) the chromatic composition of the background illumination. The combined effects of pulse light stimuli of different wavelength applied either simultaneously or in immediate sequence are reported here. The results give some insight into the possible mechanism of phototransduction.     

Effect of two microalgae concentrations on body size and egg size of the rotifer <Emphasis Type="Italic">Brachionus calyciflorus</Emphasis>

The rotifer, Brachionus calyciflorus, was grown with two algae species (Chlorella sp. and Scenedesmus obliquus) at different concentrations (0.1, 1 and 10 × 10⁶ cells ml⁻¹). The body size (lorica biovolume) of individual rotifer and their egg size were measured when the populations were roughly in the exponential phase of population growth. The body size of the rotifers differed significantly (P < 0.05) among the two algae species used, however this effect was not observed for egg size. The body size of rotifers fed on higher densities of Chlorella sp. (10 × 10⁶ cells ml⁻¹) was significantly larger than for those fed on lower and medium densities (0.1 and 1 × 10⁶ cells ml⁻¹). Body size and egg size of rotifers fed with different amounts of Scenedesmus did not differ significantly. The egg size was significantly larger at higher food level of Chlorella. A significantly positive correlation was observed between the adult rotifer body size and their egg size.     

Contrasting patterns of body size for Daphnia species that segregate by habitat

Summary We investigate how body size of two coexisting Daphnia species varies among 7 lakes that represent a gradient of predation risk. The two species segregate vertically in stratified lakes; D. galeata mendotae is typically smaller and more eplimnetic than D. pulicaria. The extent of vertical habitat partitioning, however, varies seasonally within and among lakes in apparent response to predation intensity by epilimnetic planktivorous fishes. Daphnia pulicaria uses the epilimnion at low levels of fish predation but is restricted to the hypolimnion under high fish predation, whereas D. galaeta mendotae always utilizes the epilimnion. The species display contrasting patterns of genetic variation in neonate size and size at maturity. D. pulicaria is larger in lakes with higher fish and Chaoborus densities whereas D. galeata mendotae is smaller. This contrast in body size in lakes with high predation is associated with greater habitat segregation in those lakes. In lakes with low predation risk, the two species are similar in body size at birth and maturity.Authorship order alphabetical     

温度对水螅种群增长和个体大小的影响

应用群体累积培养法,以枝角类为食物,在10℃、20℃和30℃三种温度下,研究了温度对水螅(Hydra sp．)种群密度、种群增长率和个体大小的影响。结果表明温度对水螅种群密度和个体体积由极显著影响。在培养初期,30℃下的水螅种群密度最大;而在培养后期,20℃下的水螅种群密度则显著大于30℃下的值;10℃下的值则始终最小。在同一温度下,种群增长率均与时间呈曲线相关,10℃、20℃、30℃的回归方程分别为：Y=0．000433X^2-0．00262X 0．00332、Y=-0．003367X^2 0．068335X-0．066489、Y=-0．018469X^2 0．188952X-0．030933。在研究范围内,30℃的水螅个体最小。     

Maternal body size as a morphological constraint on egg size and fecundity in butterflies

It is a widespread notion that in arthropods female reproductive output is strongly affected by female size. In butterflies egg size scales positively with female size across species, suggesting a constraint imposed by maternal size. However, in intraspecific comparisons body size often explains only a minor part of the variation in progeny size. We here include representatives of various butterfly families to test the generality of this phenomenon across butterflies. Phenotypic correlations between egg and maternal body size were inconsistent across species: correlations were non-significant for Pararge aegeria and Lycaena tityrus, significantly positive for Papilio machaon, significantly negative for Araschnia levana, and contradictory for Pieris napi. Thus, there was no general pattern linking egg size to maternal size, e.g., caused by an allometric relationship. Consequently, there was at best limited evidence for maternal size acting as a morphological constraint on egg size within butterfly species. Realized fecundity depended on maternal size in P. napi and A. levana, but not in P. aegeria, suggesting that maternal size may affect egg number more strongly than egg size. Yet, variation in fecundity was primarily explained by variation in longevity as is expected for income breeders. Heritability estimates across species were rather similar for pupal mass (ranging between 0.14 and 0.19), but more variable for egg size (0.17–0.31).