Genetic analysis of developmental mechanisms in hydra: XIV. Identification of the cell lineages responsible for the altered developmental gradients in a mutant strain,reg-16

The developmental gradients of six chimeric strains of hydra produced from a normal strain (105) and a regeneration-deficient strain (reg-16) were analyzed. The reg-16 mutant has been shown to have a lower gradient of head-activation potential and a higher gradient of head-inhibition potential than the normal 105 strain. The chimeric animals consisted of different combinations of the three self-renewing cell lineages found in hydra (the ectodermal and endodermal epithelial cell lineages and the interstitial cell lineage) from each of the parental origins. To identify the cell lineages responsible for the abnormal gradients in reg-16, the head-activation and head-inhibition potentials of these cell lineage chimeras were assayed by lateral transplantation of tissue. The results obtained have provided evidence which indicates that the defect responsible for the low head-activation potential in reg-16 resides in its ectodermal and endodermal epithelial cell lineages, whereas the defect responsible for its high head-inhibition potential resides in its endodermal epithelial and interstitial cell lineages. The cellular localization of these defects is not identical but very similar to the cellular localization of the regenerative defects in reg-16. This finding is consistent with and supports the view that the abnormalities of the developmental gradients are correlated to the reduced head regenerative capacity in reg-16.     

Positional Information and Positional Signalling in Hydra

A model is proposed for regulation and regeneration of the headend of hydra in terms of positional information, which involvestwo gradients. One is a diffusible substance made at the headend, which may be regarded as a positional signal. The otheris a more stable cellular parameter which is the positionalvalue. The rule for head end formation is that the concentrationof the diffusible substance falls a threshold amount below thepositional value. This model, for which some computer simulationis provided, can account for head end formation in a wide varietyof grafts. Evidence for a diffusable signal is provided by experimentsin which the time/distance relationships for head inhibitionby a grafted head are determined. Changes in positional valueduring regulation have been assayed and are much slower awayfrom the boundary. Polarity is interpreted in terms of the interactionbetween the two gradients. The biochemical basis of the gradientsis not known, but an approach to the problem has been made bytreating hydra with a variety of chemical agents.     

When does greater mortality increase population size? The long history and diverse mechanisms underlying the hydra effect

The phenomenon of a population increasing in response to an increase in its per-capita mortality rate has recently been termed the 'hydra effect'. This article reviews and unifies previous work on this phenomenon. Some discrete models of density-dependent growth were shown to exhibit hydra effects in 1954, but the topic was then ignored for decades. Here the history of research on the hydra effect is reviewed, and the key factors producing it are explored. Mortality that precedes overcompensatory density dependence always has the potential to produce hydra effects. Even when mortality follows density dependence, hydra effects may occur in unstable systems due to changes in the amplitude and/or form of population cycles. An increase in resource productivity due to lower consumption rates following increased consumer mortality can also produce a hydra effect. Lower consumption can come about as the result of increased satiation of the consumers or changes in behaviour of either consumer or resource species that reduce the mean attack rate. Changes in species composition of a resource community may also decrease the average attack rate. Population structure can promote hydra effects by allowing separation of the timing of density dependence and mortality, although stage-specific density dependence usually decreases hydra effects.     

Variations in tumor cell growth rates and metabolism with oxygen concentration, glucose concentration, and extracellular pH.

Tumors and multicellular tumor spheroids can develop gradients in oxygen concentration, glucose concentration, and extracellular pH as they grow. In order to calculate these gradients and assess their impact on tumor growth, it is necessary to quantify the effect of these variables on tumor cell metabolism and growth. In this work, the oxygen consumption rates, glucose consumption rates, and growth rates of EMT6/Ro mouse mammary tumor cells were measured at a variety of oxygen concentrations, glucose concentrations, and extracellular pH levels. At an extracellular pH of 7.25, the oxygen consumption rate of EMT6/Ro cells increased by nearly a factor of 2 as the glucose concentration was decreased from 5.5 mM to 0.4 mM. This effect of glucose concentration on oxygen consumption rate, however, was slight at an extracellular pH of 6.95 and disappeared completely at an extracellular pH of 6.60. The glucose consumption rate of EMT6/Ro cells increased by roughly 40% when the oxygen concentration was reduced from 0.21 mM to 0.023 mM and decreased by roughly 60% when the extracellular pH was decreased from 7.25 to 6.95. The growth rate of EMT6/Ro cells decreased with decreasing oxygen concentration and extracellular pH; however, severe conditions were required to stop cell growth (0.0082 mM oxygen and an extracellular pH of 6.60). Empirical correlations were developed from these data to express EMT6/Ro cell growth rates, oxygen consumption rates, and glucose consumption rates, as functions of oxygen concentration, glucose concentration, and extracellular pH. These empirical correlations make it possible to mathematically model the gradients in oxygen concentration, glucose concentration, and extracellular pH in EMT6/Ro multicellular spheroids by solution of the diffusion/reaction equations. Computations such as these, along with oxygen and pH microelectrode measurements in EMT6/Ro multicellular spheroids, indicated that nutrient concentration and pH levels in the inner regions of spheroids were low enough to cause significant changes in nutrient consumption rates and cell growth rates. However, pH and oxygen concentrations measured or calculated in EMT6/Ro spheroids where quiescent cells have been observed were not low enough to cause the cessation of cell growth, indicating that the observed quiescence must have been due to factors other than acidic pH, oxygen depletion, or glucose depletion.     

光周期对中国水螅种群增长、无性出芽生殖及抗氧化酶活力的影响

单细胞真核绿藻在中国水螅(Hydra sinensis)内胚层皮肌细胞中共生是有较高科研价值的特殊生物学现象。水螅宿主细胞为共生藻提供CO2、氮源及矿物质,而共生藻通过光合作用可能为宿主提供碳水化合物等有机物营养,因此水螅与共生藻间代谢流是以共生藻光合作用为中心,但基于代谢流二者间的互作机制目前尚未阐明。水螅通过营养积累进行出芽生殖,从母体脱落的芽体数量间接反映水螅营养积累的相对量。而光暴露时长能影响共生绿藻光合作用,如果共生藻的确能向水螅细胞转移光合作用产物,那光暴露时长应该能间接影响水螅的营养积累、从而进一步影响水螅无性出芽生殖。为证实该假说,本研究应用种群累积培养法,观察了光周期对中国水螅种群增长、无性出芽生殖及抗氧化酶(SOD和CAT)活力的影响。结果显示,光周期对中国水螅种群增长具有明显的影响。培养15 d后,所有实验组水螅的种群密度均为正增长,其中8L∶16D(在一个24h周期内光暴露8 h、黑暗16 h)实验组种群密度最大、而0L∶24D(持续黑暗)实验组种群密度最小。另外,随着光暴露时长的增加,中国水螅SOD及CAT活力整体均呈下降趋势。结果表明,从光周期对中国水螅无性出芽生殖及两种抗氧化酶活力的影响来看,中国水螅对光周期的生理学响应较为敏感,这个现象可能源于共生绿藻能通过向宿主细胞转移光合作用产物的方式为水螅提供营养补充。     

Genetic Analysis of Developmental Mechanisms in Hydra. XV. Nematocyte Differentiation in Strains with Altered Developmental Gradients*

Nematocyte differentiation from the interstitial stem cells in hydra occurs non-uniformly along the body column. The relative ratios of the 4 nematocyte types produced vary gradually from head to foot along the body axis (Bode and Smith, 1977). To find out whether this regional variation in nematocyte differentiation along the body column is related to the gradients of the head-activation and head-inhibition potentials, nematocyte differentiation patterns were examined in strains which have significantly different developmental gradients along their body columns. Five strains of hydra, including a wild-type, two mutant strains and two chimeric (mutnt/wild-type) strains, were investigated. It was found that the regional variations in the nematocyte differentiation were similar in all the strains examined, and that no significant differences of the variation existed that could be attributed to the differences of the developmental gradients in these strains. This suggests that nematocyte differentiation is strongly affected by the axial position along the body column, but that the gradients of the morphogenetic potentials involved in head formation are not involved in this effect. Instead, some other parameter(s) of axial position not directly associated with these gradients must be responsible for the positional effect on nematocyte differentiation.     

Glucose uptake by symbiotic Chlorella in the green-hydra symbiosis

There is a correlation between the ability of symbiotic Chlorella algae to take up glucose and their survival in green hydra grown in continuous darkness. Although normal symbionts of European green hydra, which persist at a stable level in dark-grown animals, possessed no detectable constitutive ability to take up glucose when grown in light, uptake was induced after incubation in a medium containing glucose. Further, symbionts isolated from hydra grown in darkness for two weeks had acquired a constitutive uptake ability. Neither NC64A nor 3N813A strains of algae, in artificial symbiosis with hydra, persisted in dark-grown animals, and they showed little or no uptake ability, although in culture NC64A possessed both constitutive and inducible glucose-uptake mechanisms. In contrast, mitotic indices in all three types of algae in symbiosis with hydra increased after host feeding, indicating that the factor which stimulates algal cell division is not identical to the substrate utilised during heterotrophic growth.Abbreviations E/E normal Hydra-Chlorella symbiosis - E/NC, E/3N artificial symbioses between Hydra and Chlorella strains NC64A and 3N813A, respectively - 3-OMG 3-O-methyl-D-glucose - SDS sodium dodecyl sulfate     

MITOTIC CONTROL IN ADULT MAMMALIAN TISSUES

Mitotic homeostasis: Mitotic control is maintained by the interaction of a tissue-specific mitosis-inhibiting chalone, which permeates the whole tissue, and a non-tissue-specific mitosis-promoting mesenchymal factor, which originates in the connective tissue and acts only on connective-tissue-adjacent cells. In the basal layer of the epidermis the mitotic rate is determined by the relative concentrations of these two substances; in the distal layers the chalone is dominant so that all cells must become post-mitotic, age, and die. Thus the perfect balance between cell gain and cell loss that is maintained equally in hypoplasia, normality, and hyperplasia is ensured by the fact that all cells forced distally by mitotic pressure enter a chalone concentration that is high enough to direct them into post-mitosis and so to their deaths. The mitotic rate of the basal epidermal cells and the ageing rate of the distal cells are both inversely related to the chalone concentration. A change in the mitotic rate is matched by an equal change in the ageing rate so that, within limits, epidermal thickness (or mass) remains constant. Epidermal thickness is determined by the tissue-specific ratio, mitotic rate: ageing rate; it is influenced by the mitotic rate only when this exceeds a certain critical level. Evidently all epithelial tissues, even when these form solid masses (e.g. liver hepato-cytes), have a similar control mechanism, the ‘basal cells’ being those that are connective-tissue-adjacent and the ‘distal cells' those that are not. Tissues that are not connective-tissue-based (e.g. erythrocytes and granulocytes) have specialized mechanisms involving differentiation from relatively undifferentiated stem cell populations, as also do the connective tissues themselves. Local tissue damage leads via local chalone loss to a temporarily and locally increased mitotic rate; chronic damage leads via chronic chalone loss to hyperplasia, the increase in tissue mass being limited by the reduced life-span of the post-mitotic cells. Compensatory hypertrophy When a tissue mass is so large (e.g. the hepatocytes) in relation to the total body mass that the escaping chalone forms a significant systemic concentration, extensive damage leads to compensatory hypertrophy. The reduced tissue mass (e.g. after partial hepatectomy) produces less chalone, leading to a reduced systemic concentration, and therefore a higher chalone loss from the surviving tissue. This results in a general mitotic response in that tissue, as the relative power of the mesenchymal factor increases, and thus to an increase in tissue mass. Growth ceases when the normal tissue mass is attained. When a large tissue suffers chronic damage (e.g. liver cirrhosis) the chronic chalone lack results in hypertrophy, which is limited by the reduced life-span of the post-mitotic cells. Tumour growth Mitotic control is lost when the chalone concentration falls so low that the ‘distal cells’ remain mitotic; cell gain then exceeds cell loss and a tumour appears. Such chalone loss is related to permanent membrane damage, which may be the central event in carcinogenesis. The evidence is that a tumour continues to produce and to respond to the chalone of its tissue of origin. As a tumour grows the systemic concentration of its chalone rises steadily so that there is an increasing mitotic inhibition, first, in the parent tissue, and second, in the tumour itself. Thus tumour growth may be described as an exponential process limited by an exponential retardation. This means that, if the host survives, the tumour growth will cease and the tumour mass will reach a plateau. This is a negative feedback mechanism which differs from compensatory hypertrophy only in that, at the plateau, the mass attained is greater than normal, and also in that, at any time, further cell damage may cause the tumour to ‘progress’. When this happens the new and higher plateau may be unattainable before the host is killed. Tumour growth is normally slower than would be expected if the mitotic advantage were the only factor involved; clearly tumour growth is usually inhibited by factors other than the chalone, in particular perhaps by the immune response to the altered cell membrane. It is an especial pleasure to acknowledge the constant help and encouragement that has been given by Johanna U. R. Deol.     

Tissue dynamics of steady state growth in Hydra littoralis. II. Patterns of tissue movement

In the column of hydra, tissues continually move away from a region located just underthe whorl of tentacles. Above this subtentacular region, tissues proceed into the hypostome and tentacles; below it tissues pass into the buds or continue down the stalk. These movements represent a steady state pattern of tissue renewal in which column growth is balanced by tissue loss at the body extremities. But the existence of a subtentacular zone in which tissue appears stationary does not necessarily indicate that growth is restrictedto this region, as is commonly stated. The body column of hydra can be viewed as an expanding cylinder whose elongation is balanced by tissue loss at the two ends. In such a body there must be one region from whichtissue appears to emanate, regardless of how growth is distributed along the cylinder. Only the rates at which tissues move will be characteristic of the underlying growthpattern. In Hydra littoralis, the measured rates of tissue movement down the gastric column are consistent with the distributions of mitotic figures, which indicate that growth is spread out along the column.     

A review of some physiological and evolutionary aspects of body size and bud size of Hydra

Green hydra with endosymbionts are smaller than brown asymbiotic ones. Regeneration experiments, mitotic index studies on algal and hydra tissue, and evidence for consumption and expulsion of algae are reviewed and it is suggested that larger green hydra have more difficulty controlling algal increase than smaller ones and that hydra have an upper size limit for maintenance of stable symbioses. A mathematical model is discussed which starts with simple physiological assumptions about hydra and generates field testable conclusions about how body and bud size, and reproductive rates depend on food particle size, quantity and temporal distribution. Unlike most analytic ecological-evolutionary models, this one integrates physiology, ecology and evolution without needing simplifying assumptions.     

Formulating variable carrying capacity by exploring a resource dynamics-based feedback mechanism underlying the population growth models

Most of the population growth models comprise the concept of carrying capacity presume that a stable population would have a saturation level characteristic. This indicates that the population growth models have a common implicit feature of resource-limited growth, which contributes at a later stage of population growth by forming a numerical upper bound on the population size. However, a general underlying resource dynamics of the models has not been previously explored, which is the focus of present study. In this paper, we found that there exists a conservation of energy relationship comprising the terms of available resource and population density, jointly interpreted here as total available vital energy in a confined environment. We showed that this relationship determines a density-dependent functional form of relative population growth rate and consequently the parametric equations are in the form depending upon the population density, resource concentration, and time. Thus, the derived form of relative population growth rate is essentially a feedback type, i.e., updating parametric values for the corresponding population density. This resource dynamics-based feedback approach has been implemented for formulating variable carrying capacity in a confined environment. Particularly, at a constant resource replenishment rate, a density-dependent population growth equation similar to the classic logistic equation is derived, while one of the regulating factors of the underlying resource dynamics is that the resource consumption rate is directly proportional to the resource concentration. Likewise two other population growth equations similar to two known popular growth equations are derived based on this resource dynamics-based feedback approach. Using microcosm-derived data of fungus T. virens, we fitted one derived population growth model against the datasets, and concluded that this approach is practically implementable for studying a single population growth regulation in a confined environment.     

HyAlx, an aristaless-related gene, is involved in tentacle formation in hydra

Developmental gradients are known to play important roles in axial patterning in hydra. Current efforts are directed toward elucidating the molecular basis of these gradients. We report the isolation and characterization of HyAlx, an aristaless-related gene in hydra. The expression patterns of the gene in adult hydra, as well as during bud formation, head regeneration and the formation of ectopic head structures along the body column, indicate the gene plays a role in the specification of tissue for tentacle formation. The use of RNAi provides more direct evidence for this conclusion. The different patterns of HyAlx expression during head regeneration and bud formation also provide support for a recent version of a reaction-diffusion model for axial patterning in hydra.     

HyBMP5-8b, a BMP5-8 orthologue, acts during axial patterning and tentacle formation in hydra

Developmental gradients play a central role in axial patterning in hydra. As part of the effort towards elucidating the molecular basis of these gradients as well as investigating the evolution of the mechanisms underlying axial patterning, genes encoding signaling molecules are under investigation. We report the isolation and characterization of HyBMP5-8b, a BMP5-8 orthologue, from hydra. Processes governing axial patterning are continuously active in adult hydra. Expression patterns of HyBMP5-8b in normal animals and during bud formation, hydra's asexual form of reproduction, were examined. These patterns, coupled with changes in patterns of expression in manipulated tissues during head regeneration, foot regeneration as well as under conditions that alter the positional value gradient indicate that the gene is active in two different processes. The gene plays a role in tentacle formation and in patterning the lower end of the body axis.     

Cell growth factor activity: New quantitative method in cell culture assay

This quantitative method for the assay of growth factor activity in vitro was developed empirically. Based on the empirical equations, it seems logical to express the cell growth rate by cell duplication frequency, f, and the growth factor activity by the normalized cell growth rate: $\text{1}\text{(T-T}\text{min}\text{)}$. The latter is recommended as the basis of defining an arbitrary unit of growth factor activity. For the in vitro growth factor activity assay, the quantitative method based on the empirical equations has two important features: (1) it appears to express linearly the growth factor concentration in assay, and (2) it is not affected by the initial cell counts and the length of cultivation.The view that these two features overcome the apparent defects associated with the expression systems that use the cell count ratio and net cell count is discussed. The quantitative method based on the empirical equations has been verified with experiments and compared with expression systems using the cell count ratio and net cell count. The experiments, which verified the quantitative method based on the empirical equations, were carried out with four selected cell lines: aortic endothelial cells, mouse 3T3 fibroblasts, Walker 256 carcinoma, and Chang's liver cells, using serum as the source of growth factor(s) for all cell lines. Vitreous, retinal extract, and Walker 256 carcinoma extract were also used for aortic endothelial cells.     

THE INFLUENCE OF PRECURSOR POOL SIZE ON MITOCHONDRIAL COMPOSITION IN NEUROSPORA CRASSA

The chemical composition of mitochondria obtained from exponentially growing Neurospora can be varied by addition of choline or amino acids to the culture medium. The variation affects the phospholipid to protein ratio, and the density of mitochondria as determined by isopycnic centrifugation in sucrose gradients. These variations have been observed in biochemical mutant strains as well as wild type cultures. In a choline-requiring strain, two levels of choline supplementation to the medium have been defined: a low choline concentration just adequate to support maximal logarithmic growth, and a high choline concentration which permits maximal incorporation of radioactive choline into cellular lipids. Mitochondria isolated from cultures growing at the low choline concentration have one-half the phospholipid to protein ratio of those from high choline cultures, and their density is significantly higher. Artificial mixtures of the two types of mitochondria can be resolved into two populations by isopycnic centrifugation. The concentration of cytochromes (measured by mitochondrial difference spectra) and of malate and succinate dehydrogenases (measured by enzyme activity) were the same in both types of mitochondria, on a protein basis. The results suggest that during growth of the mitochondrial mass, the incorporation of phospholipid and protein components can vary independently. Direct kinetic measurements did indeed show that choline, added to a culture growing at low choline concentration, was incorporated into mitochondrial lipids at a rate faster than the incorporation of protein. The mitochondrial phospholipid to protein ratio can also be influenced by the level of leucine supplementation to a leucine-requiring mutant, so that with leucine concentrations above those required for maximal exponential growth, mitochondria of increasing density and decreasing phospholipid to protein ratio are produced. Additions of choline or amino acids to the minimal medium of wild type cultures influence mitochondrial composition in a manner directly comparable to that observed in biochemical mutant strains. The results suggest that mitochondrial composition, in general, is determined by rates of incorporation of the two major components, phospholipid and protein; that these rates can vary independently in response to precursor concentration in the culture medium; and that they normally operate at a precursor (substrate) concentration below saturation level.     

Genomic stability of Saccharomyces cerevisiae baker's yeasts.

The objective of this study has been to gather data on genomic stability of baker's yeast strains during long-term mitotic growth under restrictive conditions so that comparisons could be made to other studies indicating genomic instability during meiosis. The work describes the analysis of mitotic stability of the nuclear and mitochondrial genomes in the baker's yeast strain V1 during incubation in continuous culture for 190 generations (300 days). The cells were cultured in complete medium containing 2% glucose and 8 to 12% ethanol, as a mutagenic agent specific for mtDNA. The high concentration of ethanol severely limited the growth rate of the cells. DNA samples were monitored for chromosomal pattern, polymorphisms in selected nuclear genes (SUC2, MALIT, ADH1) and mobile genetic elements (Ty1 and Y'), and for RFLPs in mtDNA. The results show that both the nuclear and mitochondrial genomes of grande cells were very stable. However, the frequency of petite mutants in the population varied dramatically during the course of the experiment, reaching as high as 87% petite during the first 27 days of the experiment and declining to 5.8% petite at the end. This decline can be attributed to selection against petite mutants in media containing high concentrations of ethanol. Moreover, when samples and the parental strain were compared at the end of the experiment, no change could be observed in parameters such as their growth rate in different media, capacity to leave doughs, viability in ethanol or frequency of petite mutants. Results therefore indicated that the majority of the cells in the population were very similar to the parental throughout the experiments, with no apparent molecular or phenotypical changes.     

Response of retinal ganglion cell axons to striped linear gradients of repellent guidance molecules

Although molecular gradients have long been postulated to play a role in the development of topographic projections in the nervous system, relatively little is known about how axons evaluate gradients. Do growth cones respond to concentration or to slope? Do they react suddenly or gradually? Is there adaptation? In the developing retinotectal system, temporal retinal ganglion cell axons have previously been shown to avoid repellent cell-surface activities distributed in gradients across the optic tectum. We confronted temporal retinal axons with precisely formed striped linear gradients of repellent tectal membranes and of two candidate repellent molecules, ephrin-A2 and -A5. Axons entered gradient stripes independently of their slope and extended unhindered in the uphill direction until they suddenly avoided an apparent threshold concentration of repellent material that was independent of slope. This critical concentration was similar in both linear and nonlinear gradients, and hence independent of gradient shape. When gradients of identical slope were formed on different basal levels of repellent material, axons grew uphill for a fixed increment of concentration, possibly measured from the lowest point of the gradient, rather than up to a fixed absolute concentration. The speed of growth cones was not affected by repellent unstriped gradients below the critical concentration level. Similar results were found with membranes from cell lines stably transfected with either ephrin-A5 or ephrin-A2, two previously identified growth cone repellent cell-surface proteins. These data suggest that growth cones or axons can integrate guidance information over large distances, probably by a combined memory and adaptation mechanism. © 1998 John Wiley & Sons, Inc. J Neurobiol 37: 541–562, 1998     

Symbiosis between hydra and chlorella: Molecular phylogenetic analysis and experimental study provide insight into its origin and evolution

Although many physiological studies have been reported on the symbiosis between hydra and green algae, very little information from a molecular phylogenetic aspect of symbiosis is available. In order to understand the origin and evolution of symbiosis between the two organisms, we compared the phylogenetic relationships among symbiotic green algae with the phylogenetic relationships among host hydra strains. To do so, we reconstructed molecular phylogenetic trees of several strains of symbiotic chlorella harbored in the endodermal epithelial cells of viridissima group hydra strains and investigated their congruence with the molecular phylogenetic trees of the host hydra strains. To examine the species specificity between the host and the symbiont with respect to the genetic distance, we also tried to introduce chlorella strains into two aposymbiotic strains of viridissima group hydra in which symbiotic chlorella had been eliminated in advance. We discussed the origin and history of symbiosis between hydra and green algae based on the analysis.     

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。