Hydra Development Research Articles

AI Enabled Data Quality Monitoring with Hydra

Data quality monitoring is critical to all experiments impacting the quality of any physics results. Traditionally, this is done through an alarm system, which detects low level faults, leaving higher level monitoring to human crews. Artificial Intelligence is beginning to find its way into scientific applications, but comes with difficulties, relying on the acquisition of new skill sets, either through education or acquisition, in data science. This paper will discuss the development and deployment of the Hydra monitoring system in production at Gluex. It will show how “off-the-shelf” technologies can be rapidly developed, as well as discuss what sociological hurdles must be overcome to successfully deploy such a system. Early results from production running of Hydra will also be shared as well as a future outlook for development of Hydra.

Real time dynamics of β-catenin expression during Hydra development, regeneration and Wnt signalling activation.

Understanding the dynamic cellular behaviours driving morphogenesis and regeneration is a long-standing challenge in biology. Live imaging, together with genetically encoded reporters, may provide the necessary tool to address this issue, permitting the in vivo monitoring of the spatial and temporal expression dynamics of a gene of interest during a variety of developmental processes. Canonical Wnt/β-catenin signalling controls a plethora of cellular activities during development, regeneration and adulthood throughout the animal kingdom. Several reporters have been produced in animal models to reveal sites of active Wnt signalling. In order to monitor in vivo Wnt/β-catenin signalling activity in the freshwater polyp Hydra vulgaris, we generated a β-cat-eGFP transgenic Hydra, in which eGFP is driven by the Hydra β-catenin promoter. We characterized the expression dynamics during budding, regeneration and chemical activation of the Wnt/β-cat signalling pathway using light sheet fluorescence microscopy. Live imaging of the β-cat-eGFP lines recapitulated the previously reported endogenous expression pattern of β-catenin and revealed the dynamic appearance of novel sites of Wnt/β-catenin signalling, that earlier evaded detection by mean of in situ hybridization. By combining the Wnt activity read-out efficiency of the β-catenin promoter with advanced imaging, we have created a novel model system to monitor in real time the activity of Hydra β-cat regulatory sequences in vivo, and open the path to reveal β-catenin modulation in many other physiological contexts.

A Novel Mode of Colony Formation in a Hydrozoan through Fusion of Sexually Generated Individuals

Coloniality, as displayed by most hydrozoans, is thought to confer a size advantage in substrate-limited benthic marine environments and affects nearly every aspect of a species' ecology and evolution. Hydrozoan colonies normally develop through asexual budding of polyps that remain interconnected by continuous epithelia. The clade Aplanulata is unique in that it comprises mostly solitary species, including the model organism Hydra, with only a few colonial species. We reconstruct a multigene phylogeny to trace the evolution of coloniality in Aplanulata, revealing that the ancestor of Aplanulata was solitary and that coloniality was regained in the genus Ectopleura. Examination of Ectopleura larynx development reveals a unique type of colony formation never before described in Hydrozoa, in that colonies form through sexual reproduction followed by epithelial fusion of offspring polyps to adults. We characterize the expression of manacle, a gene involved in foot development in Hydra, to determine polyp-colony boundaries. Our results suggest that stalks beneath the neck do not have polyp identity and instead are specialized structures that interconnect polyps. Epithelial fusion, brooding behavior, and the presence of a skeleton were all key factors behind the evolution of this novel pathway to coloniality in Ectopleura.

Important roles for epithelial cell peptides in hydra development

It has been convincingly shown that peptides play important roles in the regulation and maintenance of a variety of tissues and organs in living animals. However, little is known concerning the potential role of peptides as signaling molecules in developmental processes. In Hydra, there is circumstantial evidence that small diffusible molecules act as morphogens in the regulation of patterning processes. In order to view the entire spectrum of peptide signaling molecules, we initiated a project aiming at the systematic identification of peptide signaling molecules in Hydra. In this review, we describe three peptide signaling molecules and one family of peptides that function as signaling molecules in the processes of axial pattern formation and neuron differentiation in Hydra. These peptides are produced by epithelial cells and are therefore termed "epitheliopeptides". We discuss the importance of epitheliopeptides in developmental processes within a subset of hydrozoans.

From observations to paradigms; the importance of theories and models. An interview with Hans Meinhardt

Hans Meinhardt received his PhD in physics from the University of Cologne at 1966. For a postdoctoral fellowship, he went to the European High Energy Laboratory CERN in Geneva where he joined a group working on the leptonic decay of the Xi-minus particle. One of his duties was to perform computer simulations to optimize the complex experimental setup--a skill which turned out to be helpful later on. In 1969 he switched to biology and joined the department of Alfred Gierer at the Max Planck Institute for Developmental Biology (formerly Virus Research) in Tubingen. His interest was focused on mechanisms of biological pattern formation. Using computer simulations as a tool, he developed models for essential steps in development. Most fascinating for him was the possibility to recapitulate and to reconstructusing the computer the genesis of structures where no structures were before and to see how these emerging structures become subsequently further refined. In addition to the interaction with Alfred Gierer and his group working on hydra development, the Max-Planck Institute as a whole provided a very stimulating environment. In the seventies, the work of Klaus Sander on gradients in early insect development was highly influential. Collaboration with Martin Klinger in the eighties revealed that the pigmentation patterns on tropical sea shells are convenient to study highly dynamic patterning processes. The variability and the asthetic beauty of these patterns turned out to result from the chaotic nature of the underlying reactions. Mechanisms deduced from shell patterns became a key to understand other developing systems such as orientation of chemotactic cells or phyllotaxis. Officially Hans Meinhardt retired at the end of 2003. At present he works on refinements and extensions of models which account for the different modes of embryonic axis formation in different phyla from an evolutionary point of view.

Characterization of Hydra Type IV Collagen: TYPE IV COLLAGEN IS ESSENTIAL FOR HEAD REGENERATION AND ITS EXPRESSION IS UP-REGULATED UPON EXPOSURE TO GLUCOSE

Hydra vulgaris mesoglea is a primitive basement membrane that also exhibits some features of an interstitial matrix. We have characterized cDNAs that encode the full-length hydra alpha1(IV) chain. The 5169-base pair transcript encodes a protein of 1723 amino acids, including an interrupted 1455-residue collagenous domain and a 228-residue C-terminal noncollagenous domain. N-terminal sequence analyses of collagen IV peptides suggest the molecule is homotrimeric. Denatured hydra type IV collagen protein occurs as dimers and higher order aggregates held together by nonreducible cross-links. Hydra collagen IV exhibits no functional evidence for the presence of a 7 S domain. Type IV collagen is expressed by the ectoderm along the entire longitudinal axis of the animal but is most intense at the base of the tentacles at the site of battery cell transdifferentiation. Antisense studies show that inhibition of collagen IV translation causes a blockage in head regeneration, indicating its importance in normal hydra development. Exposure of adult hydra to 15 mm glucose resulted in up-regulation of type IV collagen mRNA levels within 48 h and significant thickening of the mesoglea within 14 days, suggesting that basement membrane thickening seen in diabetes may be, in evolutionary terms, an ancient glucose-mediated response.

Oocyte Development in Hydra Involves Selection from Competent Precursor Cells

We have investigated oocyte development in Hydra vulgaris, a member of one of the oldest metazoan phyla. We show that oocyte determination involves a mechanism that establishes a subset of precursor interstitial cells competent to differentiate into oocytes. The oocyte is singled out from this subset and the competence of the remaining cells to become oocytes dramatically decreases as they adopt the alternative nurse cell fate. Progression through the nurse cell differentiation program requires the presence of the oocyte. When the oocyte is removed from the egg field, nurse cells abort their differentiation program, undergo apoptosis, and are phagocytosed and degraded by somatic epithelial cells. However, in the presence of the oocyte, nurse cells differentiate and enter an unusual apoptosis program where they are phagocytosed by the oocyte, but are not degraded. We show that the oocyte is able to induce this unusual apoptosis program in immature nurse cells that have not completed differentiation. A new model for oocyte development in Hydra is discussed.

Hormonal factors from the mammalian pineal gland interfere with cell development in Hydra.

A partially purified, melatonin-free low-molecular-weight extract from the ovine pineal gland with antitumor activity (YC05R), interferes with terminal differentiation in the interstitial cell line of Hydra. Nematoblasts developed into defective nematocytes that were subject to cell death and the tentacles eventually became devoid of nematocytes. In an attempt to identify the causative components of the extract, several known potential constituents were assayed. Two factors were found to have similar effects, although only in rather high concentrations: 1alpha, 25 dihydroxyvitamin D3 (>150 nM) and pinoline (>5 microM), a natural tryptophan-derived beta-carboline. The proliferative activity in the interstitial cell line was only slightly reduced by these factors. Two other beta-carbolines that occur in the mammalian brain, harmine (10 microM) and n-butyl-beta-carboline-3-carboxylate (beta-CCB), caused the premature death of epithelial cells and thus the development of dwarfish animals which, however, continued to generate new animals by budding. The pineal extract probably contains some more, still unidentified components that interfere more potently with cell development, in Hydra as well as in mammals.

Signals and signal-transduction systems in the control of development in Hydra and Hydractinia.

Pattern control in Hydra has traditionally been assigned to the determining influence of morphogens and neuropeptides. However, at present, arachidonic acid and its derivative 12-S-HETE are the only identified, potential signal molecules known to promote head and bud formation. More potent factors might exist but are not yet identified. Nonetheless, it is possible to evoke the development of an almost unlimited number of supernumerary head structures and to induce ectopic foot formation by interference with the PI-PKC signal transducing system. Such an interference can also rescue the regeneration-deficient mutant reg-16. Regarding signals in the development of Hydractinia, metamorphosis is induced by an external key stimulus, i.e. a lipid derived from environmental bacteria. The reception of this stimulus involves PKC-mediated responses. Upon its reception, a neuropeptide is released as an internal, synchronising signal. Members of the novel LWamide family of peptides appear to represent this internal signal. In postmetamorphic development, a glycoprotein SIF serves as an inducer of stolon formation.

Neuronal control of development in hydra.

Hydra is an excellent model system for developmental biology, because pattern formation processes can be easily studied in regeneration, transplantation, and reaggregation experiments. At the cellular level hydra has the advantage that it contains only a few basic cell types and that differentiation pathways are short. Two types of signals, produced and released by nerve cells, control the spatial and temporal patterns of differentiation. Positive signals induce specific local differentiation events, and negative signals inhibit the spread of such inductions to larger areas. Head-specific growth and differentiation are controlled by head activator and head inhibitor, food-specific processes are regulated by foot activator and foot inhibitor. The activators are peptides, the inhibitors are low-molecular-weight substances. The sequence of the head activator is known, and it is conserved throughout the animal kingdom. At the cellular level head activator exerts three types of effects in hydra. It stimulates cells to divide, and it is responsible for the determination and the final differentiation of nerve cells and head-specific epithelial cells. For nerve-cell differentiation the cAMP pathway is used as second messenger system. Components of this pathway were identified in hydra. In mammals head activator is produced by nerve and neuro-endocrine cells, and it acts as mitogen on cells of neural origin. It is present early in neural development and in abnormal neural development, such as brain and neuroendocrine tumours.

Cloning and Biological Function of Laminin in Hydra vulgaris

The Cnidarian, hydra, lends itself to studies related to the role of extracellular matrix (ECM) components in development because of its high regenerative capacity and its simple structure, which is organized as an epithelial bilayer with an intervening ECM termed the mesoglea. Previous immunocytochemical and biochemical studies have established that hydra mesoglea contains many of the major matrix components (e.g., fibronectin, laminin, type IV collagen, and heparan sulfate proteoglycan) associated with the ECM of vertebrate and more complex invertebrate species. Additional studies have also established that ECM components have a critical role in hydra development as monitored during head regeneration and morphogenesis of hydra cell aggregates. In the present study a monoclonal antibody (mAb52) raised to isolated hydra mesoglea was used as a probe in additional functional studies and to screen a cDNA expression library made from poly(A)+ RNA isolated from Hydra vulgaris . Immunofluorescent analysis indicated that mAb52 was localized along the entire longitudinal axis of adult polyps in what is termed the subepithelial zones of hydra mesaglea. Cytochemical studies found these subepithelial zones to be rich in anionic sites. Previous studies have shown that mAb52 blocks hydra cell aggregate development and experiments in the current study have shown that mAb52 also blocks in vivo interstitial cell (I-cell) migration in hydra grafts. Sequence analysis of cDNA clones isolated using mAb52 indicated that the protein encoded by these clones had structural hemology with mammalian and Drosophila laminin B1 chain and hybridized to a single 6.75-kb band on Northern blots of total hydra RNA. One interesting difference in hydra laminin B1 was the presence of a FTGTQ amino acid sequence in place of the vertebrate YIGSR cell binding domain. Under nonreducing conditions, polyclonal antibodies against FTGTQ bound to the same >200-kDa band on Western blots of mesaglea as mAb52 and also immunolocalized to the subepithelial zones. Under reducing conditions, anti-FTGTQ antibodies bound to a single band with a mass of approximately 200 kDa. In addition, FTGTQ peptide inhibited adhesion of dissociated hydra cells to mesoglea and anti-FTGTQ antibodies inhibited hydra cell binding to substrates coated with mesaglea or FTGTQ peptide. Anti-FTGTQ antibodies also inhibited in vivo I-cell migration in hydra grafts. Given the early vergence of Cnidarians during evolution, these studies indicate the highly conserved nature of laminin and provide additional information regarding the critical role of ECM components during hydra development.

Ethel Browne, Hans Spemann, and the Discovery of the Organizer Phenomenon.

Ethel Browne Harvey (1885-1965) will be familiar to some as a researcher on the embryology of sea urchins. Few, however, know her as Ethel Browne who, as a graduate student, published, in 1909, a remarkable paper demonstrating for the first time the induction by a transplant of a secondary axis of polarity in the host. This process was later named "organization" by Spemann and Mangold (1924) in a paper that led to Spemann's being awarded the Nobel Prize. Why did the Nobel Committee, or other embryologists for that matter, not connect Browne's discovery with that of Spemann and Mangold? Did they consider the development of hydra as being too remote from that occurring in embryos of vertebrates? Did the 1909 paper of Ethel Browne in any way influence the thinking of Spemann or Mangold, although it was never referred to in any of Spemann's papers? In light of new information about Spemann's knowledge of Browne's work, we also can ask a number of questions about the interplay of basic prejudices in the reception accorded Browne's work.

Effects of inorganic nitrates on growth and development of Hydra

Effects of inorganic nitrates on growth and development of Hydra

Role of the neuropeptide head activator for growth and development in hydra and mammals

Role of the neuropeptide head activator for growth and development in hydra and mammals

Action of foot activator on growth and differentiation of cells in hydra

Foot activator is a small peptide found in hydra and specifically activates foot formation. I present a method for the further purification of foot activator by high-pressure liquid chromatography. The morphogenetically active fractions were assayed for their effect at the cellular level. Foot activator acts as a mitogen by pushing epithelial and interstitial cells, which are arrested in G 2, into mitosis. In the presence of foot activator, epithelial stem cells are stimulated to differentiate into foot mucus cells, and interstitial nerve precursor cells differentiate into mature nerve cells. The interaction of foot activator with head activator in the development of hydra is discussed.

Role of the neuropeptide head activator for growth and development in hydra and mammals.

In hydra, HA is produced by nerve cells and released into the intercellular space bound to large-molecular-weight carrier(s). By additional interaction with extracellular matrix components and selfinactivation by dimerisation, a local action is ensured. HA acts as a mitogen on all dividing cell types in hydra forcing them to pass through G2, divide, and either start a new round of cell division or terminally differentiate. In addition, HA is required for head-specific determination and differentiation processes. To become a head-specific nerve cell, for example, an interstitial stem cell requires HA in early S-phase to become determined to the nerve cell pathway, in late G2 to progress through mitosis, and/or in G1 to differentiate to a head-, and not to a foot-, specific nerve cell. HA (with identical amino acid sequence) occurs in other animals including mammals. In mammals, it is produced by nerve or endocrine cells and it probably acts, as in hydra, on nerve-precursor cells. On the neural cell line NH15-CA2 and on the pituitary cell line AtT20, HA acts as mitogen by stimulating cells arrested in G2 to enter mitosis. The presence of HA early in neural development and in abnormal neural development, such as in brain and neuroendocrine tumors, are consistent with a function in growth control for HA in mammals.

Morphogenetic influences of buds on pattern formation in hydra

Summary In hydra buds are thought normally to inhibit head regeneration or the formation of additional buds in the close vicinity. However we have recently demonstrated the possibility of buds developing in close vicinity of a regenerating head under experimental conditions. To further clarify this aspect of hydra development, influences of buds on head regeneration and on additional bud development were studied in Hydra attenuata. Regeneration capacity of the distal part (lacking the peduncle) and the proximal part (lacking the gastric and head zone of hydra with or without a bud. Another group of chimeras was prepared in the same way, but lacking a head. The presence of a bud in the proximal part of a regenerate generally delayed head regeneration. Significant bud induction and tentacle stimulation was Seen in chimeras each having a head and possessing a bud in both the distal and proximal parts. A slight increase in bud forming capacity was also seen in all the chimeras studied. Significantly increased numbers (14–15) of tentacles were regenerated in chimera lacking a head, except in the group with a bud only at the distal half. These results indicate that increased tissue mass generally augments bud forming capacity. However the presence of two original buds in a chimera with a head has certain synergistic effects on bud promotion. Furthermore, dynamic changes associated with head regeneration seem to be easily influenced by increased animal mass and the presence of buds to yield supernumerary tentacles in hydra. These findings indicate the positive influence of buds on head regeneration and on bud development in hydra in addition to the conventionally known negative effect on the above processes.

Epithelial cells in nerve-free hydra produce morphogenetic substances.

It has been shown that hydra, consisting almost exclusively of epithelial cells, have normal morphogenetic properties. This means that they are able to reproduce asexually by budding and to regenerate head or foot with conservation of the original polarity. Such hydra have no interstitial cells and they lack nerves and nematocytes as differentiation produces of the interstitital stem cell. Consequently, they are unable to catch or ingest food and would not survive in ntaure. However, stocks can be maintained in the laboratory, if food is injected into the gastric cavity. The fact that nerve-free hydra would grow and regenerate normally raised some doubts as to the role of the nervous system in the control of differentiation and development in hydra. In particular, the significance of morphogenetic substances, such as the head activator, which is normally produced by nerve cells, seemed to need reassessment. We now show that epithelial cells, seemed toneed reassessment. We now show that epithelial cells in hydra have the potential to produce head activator and other morphogenetic factors, but that this property is repressed in the presence of nerves.

Development of Hydra lacking nerve and interstitial cells.

Hydra attenuata were rendered free of interstitial cells (I cells) and interstitial cell derivatives by colchicine treatment. These hydra were then cloned and cultivated for 18 months and their developmental capacities were studied. Some experimental hydra possessed a few (about 1% of the normal numbers) interstitial cells and retained this low level during prolonged culture and active growth without the differentiation of I-cells into specialized cells. Other hydra were completely freed of interstitial cells by the colchicine treatment. Maceration and histological analyses showed that once a hydra is freed of all interstitial cells it does not recover them, nor do its buds contain interstitial cells. I cell-free hydra also lack nerve cells, nematocytes, gametes and endodermal gland cells, and the tissue consists only of ectodermal and endodermal epithelial cells. Hydra completely lacking interstitial cells grow, bud, exhibit tissue renewal patterns, regenerate and preserve polarity generally typical of normal hydra. I cell-free hypostomal tissue has inductive capacity, as does normal hypostomal tissue, when implanted in I cell-free or normal gastric tissue. Regenerating I cell-free tissue undergoes precocious determination as does normal tissue. Only in some quantitative aspects do I cell-free hydra develop abnormally. We conclude that hydra consisting only of epithelial cells are capable of essentially normal development.

The requirement of trace amounts of environmental sodium for the growth and development of Hydra

Trace amounts of environmental sodium ions were found to be required for the normal growth and development of Hydra. These experiments were carried out in the presence of calcium, previously shown necessary for growth [22]. None of the other ions tested could replace sodium. Concentrations of sodium as low as 10 −6 M sufficed for optimum growth and development. These findings are discussed in relation to the generally known cellular sodium requirements. The significance of controlling and investigating the milieu extérieur of fresh-water animals which lack internal extracellular fluids is emphasized.