Formation of pattern in regenerating tissue pieces of Hydra attenuata: II. Degree of proportion regulation is less in the hypostome and tentacle zone than in the tentacles and basal disc

The relative sizes of the various structures in Hydra attenuata were compared over a broad range of animal sizes to determine in detail the ability to regulate proportions during regeneration. The three components of the head, namely hypostome, tentacles, and tentacle zone from which the tentacles emerge, the body column, and the basal disc were all measured separately. Ectodermal cell number was used as the measure of size. The results showed that the basal disc proportioned exactly over a 40-fold size range, and the tentacle tissue proportioned exactly over a 20-fold size range. In contrast, the hypostome and tentacle zone proportioned allometrically. With decreasing size, the hypostome and tentacle zone became an increasing fraction of the animal at the expense of body tissue, and in the very smallest regenerates at the expense of tentacle tissue. In their current form, the reaction-diffusion models proposed for pattern regulation in hydra are not consistent with the data.     

Formation of pattern in regenerating tissue pieces of Hydra attenuata: I. Head-body proportion regulation

The precision with which an almost uniform sheet of hydra cells develops into a complete animal was measured quantitatively. Pieces of tissue of varying dimensions were cut from the body column of an adult hydra and allowed to regenerate. The regenerated animals were assayed for number of heads (hypostomes plus tentacle rings), head attempts (body tentacles), and basal discs. To ascertain whether the head and body were reformed in normal proportions, the average number of epithelial cells in the heads and bodies was measured. Pieces of tissue, from $\text{1}\text{2}$ to $\text{1}\text{20}$ an adult in size, formed heads that were a constant fraction of the regenerate. Thus, over a 10-fold size range, a proportioning mechanism was operating to divide the tissue into head area and body area quite precisely, but appeared to reach limits at the extremes of the range. However, the regenerates were not all normal miniatures with one hypostome and one basal disc. As the width-length ratio of the cut piece was increased beyond the circumference-length ratio of the intact body column, the incidence of extra hypostomes in the “head” and body tentacles and extra basal discs in the “body” rose dramatically. A proportioning mechanism based on the Gierer-Meinhardt model for pattern formation is presented to explain the results.     

Analysis of head and foot formation inHydra by means of an endogenous inhibitor

Summary In tissue regenerating the head, the ability to initiate head formation in a host increases with the time allowed for regeneration before grafting, while the foot-initiating ability decreases concomitantly. The reverse was found for tissue about to regenerate a foot. The early divergent changes thus indicated are counteracted in both head and foot regeneration by treatment with an inhibitor (Berking, 1977) in low concentrations.The inhibitor also interferes with processes which determine wether or not hypostome and tentacles are formed, and how many tentacles (if any) appear. The circumferential spacing of the tentacles was regular whether their number was normal or below normal.Secondary axes caused by implanted tissue either detach after having formed a head and a foot (i.e. behave like buds) or do not detach, having only formed a head. This alternative depends on the origin and amount of the implanted tissue and on the position of the implant within the host.The following model based on these findings is proposed: Head and foot formation start with pre-patterns which cause a continuously increasing change of the tissue's ability to initiate a head or a foot. Along the body axis this ability is determined by a graded distribution of sources. As development progresses, the high source density which accumulates in the head region causes the formation of a hypostome and tentacles; the angular spacing of tentacles is also dependent on source density. At a certain low source density foot-formation is initiated. The inhibitor counteracts the increase of source density in head-forming tissue as well as the decrease of source density in foot-forming tissue. It thus appears to be part of the mechanism which controls morphogenesis in hydra.     

Regulation in the numbers of tentacles of aggregated hydra cells

Head formation was investigated during regeneration of dissociated and aggregated cells of Hydra magnipapillata. The surface area measured at the hollowing stage was found to be a useful quantity for characterizing the size of an aggregate. Four kinds of aggregates were examined, using tissue originating from (1) whole animals, (2) apical halves, (3) decapitated animals, and (4) decapitated animals allowed to regenerate for several hours before dissociation. For aggregate types (1), (2), and (4), not all the tentacles observed at an intermediate stage of the regeneration process were localized around hypostomes: the number of such body tentacles at the intermediate stage was comparable to that of the hypostomal tentacles and was approximately proportional to the surface area. These results and others suggest that the formation of body tentacles takes place independently of hypostome formation. However, for aggregate type (3), most of the tentacles appearing at the intermediate stage were hypostomal. The correlation between the surface area and the number of tentacles at the steady state apparently resulted from a regulation process by which body tentacles decreased and hypostomal tentacles increased. It is considered that the number of body tentacles appearing at an intermediate stage of regeneration would depend on the initial level of head-activation potential and that body tentacles are formed by the local fluctuation of head-activation potential.     

The ontogeny of swimming behavior in the scyphozoan, Aurelia aurita. I. Electrophysiological analysis.

1. Electrical correlates of behavioral activity were observed in the lip and tentacles of the polyp, but none were detected during column contraction. The tentacles are the most electrically active tissue, and the potentials are conducted along the length of the tentacle, but conduction to other parts of the animal were not observed. 2. Although the tentacles of the polyp and the rhopalia of the medusa are probably homologous, the development of pacemaker activity during strobilation is not a smooth transition from tentacle contraction potentials (TCPs) to marginal ganglion potentials (MGPs). This result indicates that each pacemaker activity develops de novo. 3. Two types of behavior were observed in the polyp: local responses, and coordinated activity which involved integrated responses in several body parts. The coordinated responses indicate that neurological coordination can take place in the polyp. Furthermore, feeding and spasm in the ephyra are similar to feeding and the protective response in the polyp. This similarity suggests that both coordinated responses in the polyp are coordinated by interneural facilitation in the diffuse nerve net (DNN) as in the ephyra. 4. Swimming in the ephyra is a medusoid behavior but feeding and spasm are coordinated by the DNN and are polypoid responses. Therefore, the ephyra is a mixture of polypoid and medusoid behaviors. As the ephyra matures into an adult medusa both polypoid responses are lost, but the DNN remains to modulate pacemaker output and control marginal tentacle contractions. As development proceeds from polyp, to ephyra, to medusa, each subsequent stage acquires some new behavior while retaining some aspect from the previous stage.     

Effects of ambient flow and injury on the morphology of a fluid transport system in a bryozoan

Many organisms use fluid transport systems that are open to the external environment for suspension feeding or gas exchange. How do factors related to the environment, such as injuries and ambient currents, affect remodeling of these systems? In the bryozoan Membranipora membranacea, the lophophores (crowns of ciliated tentacles) form a canopy over the colony. The lophophores pump seawater from above the colony through themselves to capture food particles. The seawater then flows under the canopy to exit the colony at chimneys (openings in the canopy) or at the canopy edge. To test whether either ambient flow speed or injury affects remodeling of this system, I measured changes in chimney size and spacing in colonies grown in flow tanks at different ambient flow speeds, and in colonies in which I killed patches of zooids. There was no effect of either ambient flow speed or injury size on chimney remodeling. Injury did not induce chimney formation. In addition, chimneys formed at the canopy edge, indicating that high pressure under the canopy did not induce chimney formation. These results suggest that ambient flow, injury, and the pressure under the canopy may have little effect on the remodeling of this fluid transport system.     

Prey Capture Ecology of the Cubozoan Carukia barnesi

Adult Carukia barnesi medusae feed predominantly on larval fish; however, their mode of prey capture seems more complex than previously described. Our findings revealed that during light conditions, this species extends its tentacles and ‘twitches’ them frequently. This highlights the lure-like nematocyst clusters in the water column, which actively attract larval fish that are consequently stung and consumed. This fishing behavior was not observed during dark conditions, presumably to reduce energy expenditure when they are not luring visually oriented prey. We found that larger medusae have longer tentacles; however, the spacing between the nematocyst clusters is not dependent on size, suggesting that the spacing of the nematocyst clusters is important for prey capture. Additionally, larger specimens twitch their tentacles more frequently than small specimens, which correlate with their recent ontogenetic prey shift from plankton to larval fish. These results indicate that adult medusae of C. barnesi are not opportunistically grazing in the water column, but instead utilize sophisticated prey capture techniques to specifically target larval fish.     

VARIATION IN HYDRA'S TENTACLE NUMBERS AS A FUNCTION OF TEMPERATURE

Chlorohydra uiridissima whose tentacle number is altered at different temperatures, was studied to see how other developmental variables changed as a function of temperature. The results suggest that temperature is instrumental in establishing the size of bud and tentacle primordia, but the number of primordia present may play a limiting role.

Animals were cultured at 18, 23 and 28°C and shifted between the extreme temperatures. Large animals with 8 tentacles, small animals with 5 tentacles, and intermediate animals with 6 and 7 tentacles served as parents. Buds and parents were monitored daily and scored for numbers of buds and tentacles.

Temperature, not parental size, determined the size of the buds. At the lower temperature buds were produced more slowly and initiated less frequently, but occurred in greater numbers per parent and had more tentacles than at the higher temperatures. The duration of bud development also increased at lower temperature, but at the lowest temperature the duration of bud development was not correlated with tentacle numbers on buds.

Changes in the frequency of bud initiation and the duration of bud development induced by changing temperature did not parallel changes in the number of tentacles produced on buds. Animals shifted from 18°C to 28°C underwent rapid increases in the rate of bud initiation and rapid shortening in the duration of bud development, while animals shifted from 28°C to 18°C underwent equally rapid changes in the opposite directions. The number of tentacles produced on buds, however, changed slowly to that characteristic of buds acclimated to the new temperatures. The frequency of bud initiation and the duration of bud development, therefore, do not determine tentacle number.

The number of tentacles already present seems to limit possibilities for adding new tentacles. Parents with five tentacles were especially likely to undergo upward changes in their tentacle number while parents with eight tentacles were resistant to such changes.     

Feeding and wounding responses in Hydra suggest functional and structural polarization of the tentacle nervous system

The nervous system of Hydra, a freshwater cnidaria, occurs as dispersed, or diffuse, nerve net throughout the animal. It is widely accepted that in a diffuse nervous system an external stimulus is conducted in all directions over the net. Here I report observations that hydra tentacles respond to feeding and wounding stimuli in a unidirectional manner. Upon contact of a tentacle with a brine shrimp larva during feeding, tissue on the proximal side of the point of contact contracted strongly, whereas tissue on the distal side contracted only very weakly. Feeding a tentacle to which a second tentacle was grafted to the proximal end in the reversed orientation showed that unidirectional conduction, once initiated, was blocked by the reversal of polarity, demonstrating that the distal to proximal polarity of tissue is crucial for unidirectional conduction. Unidirectional conduction was obtained also by mechanically pinching the tissue. The response of tentacles devoid of neurons examined was bidirectional, demonstrating that the nervous system is responsible for the unidirectional responses. These observations suggest that polarized property of the nerve net in hydra tentacles is responsible for the unidirectional tentacle contraction.     

The influence of tissue polarity on nematocyte migration in Hydra attenuata

Influences underlying the direction of nematocyte migration in hydra were studied. Nematocytes arise by interstitial cell differentiation in the body column, and then up to 80% migrate into the ectodermal epithelial cells of the tentacles. The migration of these cells, which is clearly apically directed, may be due either to a chemotactic attraction into the hypostome and tentacles, or to a property inherent in the tissue of the body column, such as the regeneration polarity. To distinguish between these two possibilities, the rates of accumulation of ³H-proline-labeled desmoneme and stenotele nematocytes in unlabeled heads (hypostome and tentacles) grafted either basally or apically to the labeled body column were compared. Basally grafted heads, if left in place for an appropriate length of time, reversed the regeneration polarity of the tissue. In all experiments the direction of desmoneme migration was correlated with the direction (apical or basal) of the regeneration polarity of the tissue. Further, the kinetics of polarity reversal were modified by varying the grafting procedure or the environmental conditions. In every case the kinetics of reversal of desmoneme migration also paralleled the kinetics of reversal of tissue polarity. The results suggest that the direction of desmoneme migration is influenced by the regeneration polarity of the tissue. Stenotele migration was largely unaffected by tissue polarity, but behaved as though chemotactically attracted to the head.     

Size and shape in the phylum Phoronida

The lophophorate phylum Phoronida consists of about 13 species, which differ in body length and width, number of longitudinal muscles, lophophore geometry and number of lophophore tentacles. In absolute terms large species have a larger body width, more tentacles, more longitudinal muscles and greater coiling of the lophophore than small species. However, size and shape analyses suggest that with increasing size: (I) the body surface area to volume ratio increases because body length increases faster than body width; (2) the relative number longitudinal muscles decreases, and (3) the relative feeding surface area of the lophophore decreases because tentacle diameter is constant while tentacle number increases at the same rate as body length and tentacle length increases more slowly than tentacle number. Coiling and spiraling of the lophophore in large species may be an attempt to compensate for this last relationship. We suggest that the habits, mode of growth and feeding mechanism of phoronids constrain size-related changes in shape.     

水螅异常极性体轴的形成及矫正进程的观察

目的:如何建立和维持体轴是一个基本的发育生物学问题,而淡水水螅是适合进行形态发生和个体发育调控机制研究的重要模式生物。本文观察了大乳头水螅异常极性体轴的形成及矫正进程,初步探讨水螅极性体轴的维持和调控机制。方法:先切取水螅的整个头部,再获得带二根触手的口区组织。通过ABTS细胞化学染色法检测水螅基盘分子标志物过氧化物酶的表达,判别水螅基盘组织(水螅足区的末端)是否形成。结果:从40块口区组织再生得到的水螅个体中有1例极性体轴发育异常的个体,其身体两端均发育成头区,且两端的头区均具有捕食能力。随后水螅其中一端头区的触手逐渐萎缩、退化,最终该端头区转化成具有吸附能力的基盘组织。结论:水螅组织的再生涉及极性体轴的重建,而一些特殊因素可能造成临时性的水螅极性体轴调控紊乱。本研究表明水螅具备自我矫正异常极性体轴的能力。另外,本研究结果显示水螅触手可以萎缩直至退化,该现象涉及的细胞学过程可能是非常复杂的,有可能涉及到触手细胞的凋亡转化过程,也可能是触手的高度分化细胞仍然具备去分化能力、去分化后再转移到身体其他地方,其具体机制值得进一步探究。     

Morphologic variations in Blackfordia virginica (hydroidomedusae: Blackfordiidae) in coastal lagoons of Chiapas, Mexico

Blackfordia virginica is an important hydromedusae in the zooplankton of coastal lagoons at Mexico. In order to contribute to their study, morphological variations of these species were analyzed in the system of coastal lagoons of Chiapas, Mexico. A total of 503 jellyfish were studied their sizes varied from 6.1 to 9.9 mm of umbrelar diameter. The number of marginal tentacles varied from 86 to 125. A 67.7% females and 30.2% males were recognized. Only 31 jellyfish (26 females and five males) presented morphological variations of ten different types and affected the number and form of the handles, radial channels and gonads. The size of the jellyfish and the number of tentacles reflected a correlation of 0.74.     

Cytological studies of the nematocysts of Hydra. I. Desmonemes,isorhizas, cnidocils,and supporting structures

Entire hydras or tentacles were fixed in OsO(4) or in KMnO(4) and thereafter washed, dehydrated, and embedded in a methacrylate mixture. Ultrathin sections were cut on an experimental model, thermal expansion type ultramicrotome or on a Porter-Blume microtome. The sections were examined in an RCA electron microscope. Type EMU-2 D. "Squash preparations" for light microscopy, were made from the hydra mouth region and the attached tentacles. These were observed with an AO Baker interference microscope. In the mature organism, three of the four types of nematocysts normally found in hydra could be positively identified with the electron microscope. The desmonemes, the smallest type, have a dense matrix and a thin capsule. The two different types of mature isorhizas could not be distinguished with certainty. They are intermediate in size between the desmonemes and stenoteles and have a capsule with a dense matrix. The cnidocil, or triggering hair, which is composed of a dense core and a fibrillar sheath has nine supporting elements arranged in a semi-circle near its base. Twenty "supporting structures" are arranged around the nematocyst capsule and interconnections between the supporting elements and these latter structures have been observed. Development of the nematocysts involves an increase in density of the matrix. Spines can be seen in the interior of tubular structures within the capsules of the holotrichous isorhizas.     

Membrane organization in soybean seeds during hydration

The ability of seeds to withstand dehydration indicates that their membranes may maintain structural integrity even when dry. Analysis of polar lipids (the principal lipidic constituents of the membranes) from soybean seeds (Glycine-max (L.) Merr.) by X-ray diffraction indicated that even in the dehydrated state the lipids retained a lamellar (bilayer) configuration. As the degree of hydration was raised, evidence of some structural alteration (apparent as an abrupt increase in bilayer spacing) was obtained from diffraction patterns of both the extracted lipid and particles of seed tissue. In seed tissue this increase in bilayer spacing occurred at a hydration level just above that at which free water could be detected by nuclear-magnetic-resonance analysis. The water content at which the increase in bilayer spacing occurred was higher in the seed tissue than in the extracted polar lipids, probably because other cell components restricted the availability of free water in the seed.Abbreviation NMR nuclear-magnetic resonance     

A histochemical study on the snout tentacles and snout skin of bristlenose catfish Ancistrus triradiatus

Histological sections of the tentacles of Ancistrus triradiatus revealed that they contain many goblet cells with granule-like sections distributed along the edge of the tentacles (mean 302 cells mm⁻¹). Various histochemical methods were used to characterize the contents of the goblet cells. The results indicated that the contents were periodic acid-Schiff (PAS) positive, glycogen negative and no sulphated mucins could be found. The contents of the goblet cells were acid mucins and O-acetylated sialomucins which had high energy content. The snout skin of the male also contained goblet cells with higher density (mean 755 cells mm⁻¹) than that of the tentacles. Snout skin of female A. triradiatus , on the contrary, did not contain any goblet cells. Instead, many minute spines could be found. Based on the acid mucins and O-acetylated sialomucins secretions of goblet cells which are of high nutritional values, it is hypothesized that snout tentacle secretions are used to provide nutrients to fish larvae when they are under paternal care.     

Head activator does not qualitatively alter head morphology in regenerates ofHydra oligactis

Summary The characterization of head activator (HA) as a morphogen capable of increasing the number of tentacles regenerated by hydra was re-examined. Gastric tissue was excised from HA-treated whole animals and allowed to regenerate. At the cellular level the differentiation of head-specific ectodermal epithelial cells was monitored by quantifying monoclonal antibody, CP8, labeling. This labeling has been correlated with a rise in head activation potential and the determination of tissue to form head structures (Javois et al. 1986). At the morphological level tentacle number was monitored. HA-treated regenerates began the head patterning processes and evaginated tentacles sooner than controls but did not produce extra tentacles. The kinetics of CP8 labeling did not reveal major differences between treated and control regenerates after the initiation of head-specific epithelial cell differentiation. HA appeared to act more like a growth factor stimulating the differentiation of head-specific cell types rather than a morphogen which altered head morphology. An additional aspect of the study examined axial-specific effects of HA on the initiation and extent of head-specific epithelial cell differentiation. The cellular response of ectodermal epithelial cells to HA was dependent on their original axial location. More CP8⁺ tissue differentiated in regenerates of apical as opposed to mid-gastric origin.     

Chronological and spatial analysis of the 1996 Ebola Reston virus outbreak in a monkey breeding facility in the Philippines.

To describe the transmission pattern of natural infection with Ebola Reston (EBO-R) virus in a breeding colony, the chronological and spatial analysis of mortality during the 1996 EBO-R virus outbreak was done in this study. The EBO-R virus infection among monkeys in the facility was widespread. Over a period of 3 months, 14 out of 21 occupied units were contaminated with antigen positive animals. A large number of wild-caught monkeys were involved in this outbreak suggesting that wild-caught monkeys have a high susceptibility to EBO-R virus infection. In this outbreak, morbidity patterns for individual animal units were very different regardless of the type and size of cages, individual or gang cages. The results suggest that not only the cage size but also poor animal husbandry practices may be risk factors for the spread of EBO-R infection.     

Effects of thermal and oxygen conditions during development on cell size in the common rough woodlice Porcellio scaber

During development, cells may adjust their size to balance between the tissue metabolic demand and the oxygen and resource supply: Small cells may effectively absorb oxygen and nutrients, but the relatively large area of the plasma membrane requires costly maintenance. Consequently, warm and hypoxic environments should favor ectotherms with small cells to meet increased metabolic demand by oxygen supply. To test these predictions, we compared cell size (hindgut epithelium, hepatopancreas B cells, ommatidia) in common rough woodlice (Porcellio scaber) that were developed under four developmental conditions designated by two temperatures (15 or 22°C) and two air O₂ concentrations (10% or 22%). To test whether small‐cell woodlice cope better under increased metabolic demand, the CO₂ production of each woodlouse was measured under cold, normoxic conditions and under warm, hypoxic conditions, and the magnitude of metabolic increase (MMI) was calculated. Cell sizes were highly intercorrelated, indicative of organism‐wide mechanisms of cell cycle control. Cell size differences among woodlice were largely linked with body size changes (larger cells in larger woodlice) and to a lesser degree with oxygen conditions (development of smaller cells under hypoxia), but not with temperature. Developmental conditions did not affect MMI, and contrary to predictions, large woodlice with large cells showed higher MMI than small woodlice with small cells. We also observed complex patterns of sexual difference in the size of hepatopancreatic cells and the size and number of ommatidia, which are indicative of sex differences in reproductive biology. We conclude that existing theories about the adaptiveness of cell size do not satisfactorily explain the patterns in cell size and metabolic performance observed here in P. scaber. Thus, future studies addressing physiological effects of cell size variance should simultaneously consider different organismal elements that can be involved in sustaining the metabolic demands of tissue, such as the characteristics of gas‐exchange organs and O₂‐binding proteins.     

Heat transfer normal to paired arterioles and venules embedded in perfused tissue during hyperthermia

A numerical model of the heat transer normal to an arteriole-venule pair embedded in muscle tissue has been constructed. Anatomical data describing the blood vessel size, spacing, and density have been incorporated into the model. This model computes temperatures along the vessel walls as well as the temperature throughout the tissue which comprises an infinitely long Krogh cylinder around the vessel pair. Tissue temperatures were computed in the steady-state under resting conditions, while transient calculations were made under hyperthermic conditions. Results show that for both large- (1st generation) and medium-sized (5th generation) vessel pairs, the mean tissue temperature within the tissue cylinder is not equal to the mean of the arteriole and venule blood temperatures under both steady-state and transient conditions. The numerical data were reduced so that a comparison could be made with the predictions of a simple two-dimensional superposition of line sources and sinks presented by Baish et al. This comparison reveals that the superposition model accurately describes the heat transfer effects during hyperthermia, permitting subsequent incorporation of this theory into a realistic three-dimensional model of heat transfer in a whole limb during hyperthermia.