Three digestive movements in<Emphasis Type="Italic"> Hydra</Emphasis> regulated by the diffuse nerve net in the body column

The mammalian digestive tract undergoes various digestive movements such as peristalsis and segmentation movement. How those digestive movements and the underlying mechanisms appeared in evolution remains unraveled. A widely accepted view has been that, early in evolution, the digestive process was static based upon diffusion, and later it became dynamic involving digestive movements. Here, we report digestive movements which occur in Hydra, a member of the phylum Cnidaria. We find that the body column of Hydra undergoes a series of movements when fed with Artemia. Comparison of the movements to those in mammals showed similarities in appearance to esophageal reflex, segmentation movement, and defecation reflex. When nerve cells were eliminated, polyps showed only a weak segmentation movement, demonstrating that the diffuse nerve net in the body column of Hydra primarily regulates the movements just as the netlike enteric nervous system does in mammals. Elimination of both secretory gland cells and nerve cells resulted in the complete loss of movement, suggesting that the gland cells are involved in the weak movement. Overall, these observations suggest that the digestive process in Hydra is dynamic and that the diffuse nerve net regulates the digestive movements as a primitive form of enteric nervous system.     

The Hydra small ubiquitin‐like modifier

SUMO is a protein posttranslational modifier. SUMO cycle components are believed to be conserved in all eukaryotes. Proteomic analyses have lead to the identification a wealth of SUMO targets that are involved in almost every cellular function in eukaryotes. In this article, we describe the characterization of SUMO Cycle components in Hydra, a Cnidarian with an ability to regenerate body parts. In cells, the translated SUMO polypeptide cannot conjugate to a substrate protein unless the C‐terminal tail is cleaved, exposing the di‐Glycine motif. This critical task is done by SUMO proteases that in addition to SUMO maturation are also involved in deconjugating SUMO from its substrate. We describe the identification, bioinformatics analysis, cloning, and biochemical characterization of Hydra SUMO cycle components, with a focus on SUMO and SUMO proteases. We demonstrate that the ability of SUMO proteases to process immature SUMO is conserved from Hydra to flies. A transgenic Hydra, expressing a SUMO‐GFP fusion protein under a constitutive actin promoter, is generated in an attempt to monitor the SUMO Cycle in vivo as also to purify and identify SUMO targets in Hydra. genesis 51:619–629. © 2013 Wiley Periodicals, Inc.     

Regionalized nervous system in Hydra and the mechanism of its development

The last common ancestor of Bilateria and Cnidaria is considered to develop a nervous system over 500 million years ago. Despite the long course of evolution, many of the neuron-related genes, which are active in Bilateria, are also found in the cnidarian Hydra. Thus, Hydra is a good model to study the putative primitive nervous system in the last common ancestor that had the great potential to evolve to a more advanced one. Regionalization of the nervous system is one of the advanced features of bilaterian nervous system. Although a regionalized nervous system is already known to be present in Hydra, its developmental mechanisms are poorly understood. In this study we show how it is formed and maintained, focusing on the neuropeptide Hym-176 gene and its paralogs. First, we demonstrate that four axially localized neuron subsets that express different combination of the neuropeptide Hym-176 gene and its paralogs cover almost an entire body, forming a regionalized nervous system in Hydra. Second, we show that positional information governed by the Wnt signaling pathway plays a key role in determining the regional specificity of the neuron subsets as is the case in bilaterians. Finally, we demonstrated two basic mechanisms, regionally restricted new differentiation and phenotypic conversion, both of which are in part conserved in bilaterians, are involved in maintaining boundaries between the neuron subsets. Therefore, this study is the first comprehensive analysis of the anatomy and developmental regulation of the divergently evolved and axially regionalized peptidergic nervous system in Hydra, implicating an ancestral origin of neural regionalization.     

Further characterization of the PW peptide family that inhibits neuron differentiation in <Emphasis Type="Italic">Hydra</Emphasis>

From an evolutionary point of view, Hydra has one of the most primitive nervous systems among metazoans. Two different groups of peptides that affect neuron differentiation were identified in a systematic screening of peptide signaling molecules in Hydra. Within the first group of peptides, a neuropeptide, Hym-355, was previously shown to positively regulate neuron differentiation. The second group of peptides encompasses the PW family of peptides that negatively regulate neuron differentiation. In this study, we identified the gene encoding PW peptide preprohormone. Moreover, we made the antibody that specifically recognizes LPW. In situ hybridization and immunohistochemical analyses showed that the PW peptides and the gene encoding them were expressed in ectodermal epithelial cells throughout the body except for the basal disk. The PW peptides are produced by epithelial cells and are therefore termed “epitheliopeptides.” Together with Hym-355, the PW family peptides mediate communication between neurons and epithelial cells and thereby maintain a specific density of neurons in Hydra. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Toshio Takahashi, Osamu Koizumi equally contributed to this study.     

Antisera to the sequence Arg-Phe-amide visualize neuronal centralization in hydroid polyps

Summary Antisera to the sequence Arg-Phe-amide (RF-amide) have a high affinity to the nervous system of fixed hydroid polyps. Whole-mount incubations of several Hydra species with RFamide antisera visualize the three-dimensional structure of an ectodermal nervous system in the hypostome, tentacles, gastric region and peduncle. In the hypostome of Hydra attenuata a ganglion-like structure occurs, consisting of numerous sensory cells located in a region around the mouth opening and a dense plexus of processes which project mostly radially towards the bases of the tentacles. In Hydra oligactis an ectodermal nerve ring was observed lying at the border of hypostome and tentacle bases. This nerve ring consists of a few large ganglion cells with thick processes forming a circle around the hypostome. This is the first direct demonstration of a nerve ring in a hydroid polyp.Incubation of Hydractinia echinata gastrozooids with RFamide antisera visualizes an extremly dense plexus of neuronal processes in body and head regions. A ring of sensory cells around the mouth opening is the first group of neurons to show RFamide immunoreactivity during the development of a primary polyp. In gonozooids the oocytes and spermatophores are covered with strongly immunoreactive neurons.All examples of whole-mount incubations with RF-amide antisera clearly show that hydroid polyps have by no means a diffuse nerve net, as is often believed, and that neuronal centralization and plexus formation are common in these animals. The examples also show that treatment of intact fixed animals with RFamide antisera is a useful technique to study the anatomy or development of a principal portion of the hydroid nervous system.     

Generation of a NK1R‐CreER knockin mouse strain to study cells involved in Neurokinin 1 Receptor signaling

The Neurokinin 1 Receptor (NK1R), which binds Substance P, is expressed in discrete populations of neurons throughout the nervous system, where it has numerous roles including the modulation of pain and affective behaviors. Here, we report the generation of a NK1R‐CreER knockin allele, in which CreER^T2 replaces the coding sequence of the TACR1 gene (encoding NK1R) in order to gain genetic access to these cells. We find that the NK1R‐CreER allele mediates recombination in many regions of the nervous system that are important in pain and anxiety including the amygdala, hypothalamus, frontal cortex, raphe nucleus, and dorsal horn of the spinal cord. Other cell types that are labeled by this allele include amacrine cells in the retina and fibroblasts in the skin. Thus, the NK1R‐CreER mouse line is a valuable new tool for conditional gene manipulation enabling the visualization and manipulation of cells that express NK1R.     

Is homarine a morphogen in the marine hydroid Hydractinia?

Summary Homogenate of coelenterate tissue interferes with metamorphosis in Hydractinia and pattern formation in both Hydractinia, and Hydra. From the extracts two fractions comprising low-molecular-weight compounds with strong metamorphosis-inhibiting activity were separated. One of these contains, as the active compound, homarine (N-methyl picolinic acid). Homarine concentrations down to 10^–6 mol/l stop or retard metamorphosis. High concentrations block the continuation of metamorphosis as long as they are maintained in the culture medium and treatment with homarine during metamorphosis influences the proportioning of the future polyp's body pattern. Most of the homarine found in Hydra tissue derives from Artemia given as food. It is not identical with inhibitor I, an activity partially purified from Hydra tissue, which prevents head and foot formation in Hydra.     

Cell lineage and cis-regulation for a unique GABAergic/glycinergic neuron type in the larval nerve cord of the ascidian Ciona intestinalis

The tunicate Ciona intestinalis larva has a simple central nervous system (CNS), consisting of fewer than 400 cells, which is homologous to the vertebrate CNS. Recent studies have revealed neuronal types and networks in the larval CNS of C. intestinalis, yet their cell lineage and the molecular mechanism by which particular types of neurons are specified and differentiate remain poorly understood. Here, we report cell lineage origin and a cis‐regulatory module for the anterior caudal inhibitory neurons (ACINs), a putative component of the central pattern generator regulating swimming locomotion. The vesicular GABA/glycine transporter gene Ci‐VGAT, a specific marker for GABAergic/glycinergic neurons, is expressed in distinct sets of neurons, including ACINs of the tail nerve cord and others in the brain vesicle and motor ganglion. Comparative genomics analysis between C. intestinalis and Ciona savignyi and functional analysis in vivo identified the cis‐regulatory module responsible for Ci‐VGAT expression in ACINs. Our cell lineage analyses inferred that ACINs derive from A11.116 cells, which have been thought to solely give rise to glial ependymal cells of the lateral wall of the nerve cord. The present findings will provide a solid basis for future studies addressing the molecular mechanism underlying specification of ACINs, which play a critical role in controlling larval locomotion.     

The Drosophila ortholog of the Zc3h14 RNA binding protein acts within neurons to pattern axon projection in the developing brain

The dNab2 polyadenosine RNA binding protein is the D. melanogaster ortholog of the vertebrate ZC3H14 protein, which is lost in a form of inherited intellectual disability (ID). Human ZC3H14 can rescue D. melanogaster dNab2 mutant phenotypes when expressed in all neurons of the developing nervous system, suggesting that dNab2/ZC3H14 performs well‐conserved roles in neurons. However, the cellular and molecular requirements for dNab2/ZC3H14 in the developing nervous system have not been defined in any organism. Here we show that dNab2 is autonomously required within neurons to pattern axon projection from Kenyon neurons into the mushroom bodies, which are required for associative olfactory learning and memory in insects. Mushroom body axons lacking dNab2 project aberrantly across the brain midline and also show evidence of defective branching. Coupled with the prior finding that ZC3H14 is highly expressed in rodent hippocampal neurons, this requirement for dNab2 in mushroom body neurons suggests that dNab2/ZC3H14 has a conserved role in supporting axon projection and branching. Consistent with this idea, loss of dNab2 impairs short‐term memory in a courtship conditioning assay. Taken together these results reveal a cell‐autonomous requirement for the dNab2 RNA binding protein in mushroom body development and provide a window into potential neurodevelopmental functions of the human ZC3H14 protein. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 93–106, 2016     

An IQGAP-related gene is activated during tentacle formation in the simple metazoan Hydra

Differentiation of body column epithelial cells into tentacle epithelial cells in Hydra is accompanied by changes in both cell shape and cell-cell contact. The molecular mechanism by which epithelial cells acquire tentacle cell characteristics is unknown. Here we report that expression of a Hydra homologue of the mammalian IQGAP1 protein is strongly upregulated during tentacle formation. Like mammalian IQGAP, Hydra IQGAP1 contains an N-terminal calponin-homology domain, IQ repeats and a conserved C terminus. In adult polyps a high level of Hydra IQGAP1 mRNA is detected at the basis of tentacles. Consistent with a role in tentacle formation, IQGAP1 expression is activated during head regeneration and budding at a time when tentacles are emerging. The observations support the previous hypothesis that IQGAP proteins are involved in cytoskeletal as well as cell-cell contact rearrangements. Received: 25 January 2000 / Accepted: 2 May 2000     

DILP‐producing median neurosecretory cells in the Drosophila brain mediate the response of lifespan to nutrition

Dietary restriction extends lifespan in diverse organisms, but the gene regulatory mechanisms and tissues mediating the increased survival are still unclear. Studies in worms and flies have revealed a number of candidate mechanisms, including the target of rapamycin and insulin/IGF‐like signalling (IIS) pathways and suggested a specific role for the nervous system in mediating the response. A pair of sensory neurons in Caenorhabditis elegans has been found to specifically mediate DR lifespan extension, but a neuronal focus in the Drosophila nervous system has not yet been identified. We have previously shown that reducing IIS via the partial ablation of median neurosecretory cells in the Drosophila adult brain, which produce three of the seven fly insulin‐like peptides, extends lifespan. Here, we show that these cells are required to mediate the response of lifespan to full feeding in a yeast dilution DR regime and that they appear to do so by mechanisms that involve both altered IIS and other endocrine effects. We also present evidence of an interaction between these mNSCs, nutrition and sleep, further emphasising the functional homology between the DILP‐producing neurosecretory cells in the Drosophila brain and the hypothalamus of mammals in their roles as integration sites of many inputs for the control of lifespan and behaviour.     

Counterbalance between BAG and URX neurons via guanylate cyclases controls lifespan homeostasis in C. elegans

Lifespan of C. elegans is affected by the nervous system; however, the underlying neural integration still remains unclear. In this work, we targeted an antagonistic neural system consisting of low‐oxygen sensing BAG neurons and high‐oxygen sensing URX neurons. While ablation of BAG neurons increases lifespan of C. elegans, ablation of URX neurons decreases lifespan. Genetic analysis revealed that BAG and URX neurons counterbalance each other via different guanylate cyclases (GCYs) to control lifespan balance. Lifespan‐modulating effects of GCYs in these neurons are independent of the actions from insulin/IGF‐1 signalling, germline signalling, sensory perception, or dietary restriction. Given the known gas‐sensing property of these neurons, we profiled that lifespan of C. elegans is promoted under moderately low oxygen (4–12%) or moderately high carbon dioxide (5%) but inhibited under high‐level oxygen (40%); however, these pro‐longevity and anti‐longevity effects are counteracted, respectively, by BAG and URX neurons via different GCYs. In conclusion, BAG and URX neurons work as a neural‐regulatory system to counterbalance each other via different GCYs to control lifespan homeostasis.     

Involvement of nitric oxide in the head regeneration of Hydra vulgaris

Recent data have shown that a functional NO-cGMP signalling system plays an important role during development and seems to be operative early during the differentiation of embryonic stem cells. The intriguing possibility exists that this role can be evolutionarily conserved between vertebrates and invertebrates. In this paper, we have analyzed the effect of NO-cGMP pathway on the regeneration process in Hydra vulgaris, the most primitive invertebrate possessing a nervous system. Our results indicate that NO production increased during Hydra regeneration. The NOS inhibitor L-NAME reduced the regenerative process and the same effect was obtained by treatment with either the specific guanylate cyclase inhibitor ODQ or the protein kinase G (PKG) inhibitor KT-5823. In contrast, the regeneration process was increased by treating decapitated Hydra with the NO donor NOC-18. Furthermore, we found that cell proliferation was also increased by treating decapitated Hydra with the NO donor NOC-18 and reduced by treatment with the NOS inhibitor L-NAME. Our results strongly suggest that the NO-cGMP-PKG pathway is involved in the control of the proliferative-differentiative patterns of developing and regenerating structures in cnidarians as well as bilaterians.     

Inhibition of protein kinase A in murine enteric neurons causes lethal intestinal pseudo‐obstruction

A number of in vitro studies suggest that many important developmental and functional events in the enteric nervous system are regulated by the intracellular signaling enzyme cAMP protein kinase A (PKA). To evaluate the in vivo significance of these observations, a Cre‐inducible, dominant‐negative, mutant regulatory subunit (RIαB) of PKA was activated in enteric neurons by either a Proteolipid protein‐Cre transgene or a Hox11L1‐Cre “knock‐in” allele. In both models, RIαB activation resulted consistently in profound distension of the proximal small intestine within 2 weeks after birth. Intestinal transit of radio‐opaque tracers was severely retarded in the double‐transgenic animals, which died shortly after weaning. In the enteric nervous system, recombination was restricted to neurons as demonstrated by histochemical analysis and confocal microscopic colocalization of a Cre recombinase‐dependent reporter gene with the neuronal marker Hu(C/D), in contrast with the glial marker S100. Histochemical analysis of β‐galactosidase expression and acetylcholinesterase activity, as well as neuronal counts, demonstrated that intestinal dysmotility was not associated with obvious malformation of the myenteric plexus. However, inhibition of PKA activity in enteric neurons disrupted the major motor complexes of isolated intestinal segments in vitro. These results provide strong evidence that PKA activity plays a critical role in enteric neurotransmission in vivo, and highlight neuronal PKA or related signaling molecules as potential therapeutic targets in gastrointestinal motility disorders. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2006     

Aminergic neurons: State control and plasticity in three model systems

Aminergic neurons have particular functions in many systems, and in this review their role is discussed and compared in three systems: those parts of the central nervous system controlling sleep and waking in the cat; the superior cervical ganglion; and the isolated nervous system of Aplysia.In the cat the aminergic neurons are most important in a waking state during which time external information is received, processed, and can be retrieved, and during which time habituation and sensitization occur. Aminergic neurons appear to have similar roles in state control in plasticity in both the Aplysianervous system and the superior cervical ganglion. The striking similarities in the role of aminergic neurons in these three systems support the speculation that aminergic neurons have uniquely important roles in regulation of the plastic properties of neurons.     

Environmental condition related reproductive strategies and sex ratio in hydras

Kaliszewicz, A. and Lipińska, A. 2011. Environmental condition related reproductive strategies and sex ratio in hydras. —Acta Zoologica (Stockholm) 00 :1–7. Temperature and food supply appeared to affect sex ratio, sex composition and percentage of sexual individuals in three Hydra species: Hydra vulgaris, Hydra circumcincta and Hydra viridissima. We found three sexes present: females, males and hermaphrodites depending on environmental conditions. Hydra vulgaris appeared to be a species with a temperature‐dependent sex determination (TSD). The males and hermaphrodites were present only under rising temperatures, whereas females were observed exclusively at lowering temperatures. Hydras reproduced asexually at constant room temperature. Unlimited food affected sex ratios and induced the presence of males in H. circumcincta at lowering temperatures. Thus, H. circumcincta may be recognised as another Hydra species in which sex is determined by environmental factors (ESD). Under rising temperatures, the number of hermaphroditic individuals was higher when food supply was unlimited in all three species, indicating that hermaphrodites may need more energy to produce both male and female gonads. Both temperature changes and food supply positively affected asexual reproductive strategies in hydras, especially budding rates. Hydra circumcincta appeared to be less agile than other hydras and able to self‐fertilise. It is likely that self‐fertilisation is an adaptation to the low probability of meeting a mate belonging to the other clone.