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Toshitaka Fujisawa

Publications and source records attributed to Toshitaka Fujisawa.

14 recordsLinked to original sources
PubMed2006

Degeneration after sexual differentiation in hydra and its relevance to the evolution of aging.

Aging occurs in most multicellular animals, yet some primitive animals do not show any sign of aging. This raises the following question: How have metazoans acquired the trait of aging in the course of evolution? Comparative studies of various species have provided a clue to this question by showing that sexually reproducing organisms predominantly undergo aging. The evolutionary theory "pleiotropy" also postulates aging as a price for facilitating the reproduction in the early life stage of an organism. For investigating the association between sexual reproduction and aging, a sexual phase-inducible organism in a laboratory would be suitable. One of such organisms is hydra, a genus of Cnidaria. Asexual hydra has been considered to be immortal, but there is the possibility that hydra undergoes aging after sexual reproduction. To search for signs of aging in hydra, we studied sexually differentiated Hydra oligactis at the individual and cellular levels. As a result, we found a significant decline in the capacities for food capture, contractile movements, and reproduction. More importantly, we discovered an exponential increase in the mortality rate of the population. These observations suggest that the degenerative process in H. oligactis represents the aging process. Furthermore, we found that the number of germ cells increased, whereas the number of somatic cells concomitantly decreased. The observed change of the cell composition is thus consistent with the "pleiotropy" theory of aging.

Animals↗
PubMed2005

Motility of endodermal epithelial cells plays a major role in reorganizing the two epithelial layers in Hydra.

Cell-cell interactions and cell rearrangements play important roles during development. Aggregates of Hydra cells reorganize into the two epithelial layers and subsequently form a normal animal. Examination of the formation of the two layers under various situations, indicates that the motility of endodermal epithelial cells, but not the differential adhesive forces of the two types of epithelial cells, plays the critical role in setting up the two epithelial layers. (1) When aggregates of ectodermal cells and of endodermal cells were placed in direct contact, the endodermal cells migrated into the interior of the ectodermal aggregate. This process was completely inhibited by cytochalasin B although initial firm attachment between the two aggregates was not blocked. (2) A single endodermal epithelial cell placed in contact with an ectodermal aggregate, actively extended pseudopod-like structures and migrated toward the center of the ectodermal aggregate. In contrast, an ectodermal epithelial cell remained in contact with an endodermal aggregate and never exhibited migratory behavior. Cytochalasin treatment of only endodermal epithelial cells abolished the migration. (3) One to 4 endodermal epithelial cells and/or ectodermal epithelial cells were placed in contact with one another forming up to 4-cell aggregates. Endodermal epithelial cells exhibited high motility that can be attributed to the migratory movement described above. Finally, formation of actin bundles, as visualized with rhodamine-phalloidin, was always correlated with pseudopod formation in endodermal epithelial cells during early and mid stages of aggregate formation.

Animals↗
PubMed2005

Hym-301, a novel peptide, regulates the number of tentacles formed in hydra.

Hym-301 is a peptide that was discovered as part of a project aimed at isolating novel peptides from hydra. We have isolated and characterized the gene Hym-301, which encodes this peptide. In an adult, the gene is expressed in the ectoderm of the tentacle zone and hypostome, but not in the tentacles. It is also expressed in the developing head during bud formation and head regeneration. Treatment of regenerating heads with the peptide resulted in an increase in the number of tentacles formed, while treatment with Hym-301 dsRNA resulted in a reduction of tentacles formed as the head developed during bud formation or head regeneration. The expression patterns plus these manipulations indicate the gene has a role in tentacle formation. Furthermore, treatment of epithelial animals indicates the gene directly affects the epithelial cells that form the tentacles. Raising the head activation gradient, a morphogenetic gradient that controls axial patterning in hydra, throughout the body column results in extending the range of Hym-301 expression down the body column. This indicates the range of expression of the gene appears to be controlled by this gradient. Thus, Hym-301 is involved in axial patterning in hydra, and specifically in the regulation of the number of tentacles formed.

Amino Acid Sequence↗
PubMed2004

Involvement of Hydra achaete-scute gene CnASH in the differentiation pathway of sensory neurons in the tentacles.

The proneural genes of achaete-scute (ac-sc) family that encodes the bHLH class transcription factors play a variety of roles in neurogenesis. In Hydra, the ac-sc homologue CnASH is involved in nematocyte differentiation. In the present study, we found that sensory neurons in the tentacles expressed CnASH, in addition to differentiating nematocytes in the body column of Hydra. Neuron precursors that migrated to the tentacle base did not express CnASH, and it took 1 day for them to become CnASH-expressing neurons. Thus, the CnASH-positive cells at the tentacle base appeared to be sensory cells at early stages of differentiation. Furthermore, the CnASH-positive neurons distributed from the base to the tip of tentacles suggest that the gene is also involved in maintenance of the differentiated state. In addition, we found that the sensory neurons in the tentacles consist of at least two subpopulations. The comparison of the CnASH expression with Nv1 expression in sensory cells that is detected by monoclonal antibody Nv1 showed that at least Nv1-positive/ CnASH-positive and Nv1-negative/ CnASH-positive sensory neurons existed in the tentacles.

Animals↗
PubMed2004

Unique catabolic pathway of glycosphingolipids in a hydrozoan, Hydra magnipapillata, involving endoglycoceramidase.

Endoglycoceramidase (EGCase; EC 3.2.1.123) is an enzyme capable of cleaving the glycosidic linkage between oligosaccharides and ceramides of various glycosphingolipids. We detected strong EGCase activity in animals belonging to Cnidaria, Mollusca, and Annelida and cloned the enzyme from a hydra, Hydra magnipapillata. The hydra EGCase, consisting of 517 amino acid residues, showed 19.2% and 50.2% identity to the Rhodcoccus and jellyfish EGCases, respectively. The recombinant hydra enzyme, expressed in CHOP (Chinese hamster ovary cells expressing polyoma LT antigen) cells, hydrolyzed [14C]GM1a to produce [14C]ceramide with a pH optimum at 3.0-3.5. Whole mount in situ hybridization and immunocytochemical analysis revealed that EGCase was widely expressed in the endodermal layer, especially in digestive cells. GM1a injected into the gastric cavity was incorporated and then directly catabolized by EGCase to produce GM1a-oligosaccharide and ceramide, which were further degraded by exoglycosidases and ceramidase, respectively. However, hydra exoglycosidases did not hydrolyze GM1a directly. These results indicate that the EGCase is indispensable for the catabolic processing of dietary glycosphingolipids in hydra, demonstrating the unique catabolic pathway for glyosphingolipids in the animal.

Amino Acid Sequence↗
PubMed2004

Three digestive movements in Hydra 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.

Animals↗
PubMed2003

Hydra regeneration and epitheliopeptides.

Hydra has been well known for over 200 years for its remarkable regenerative capacity. In addition to small pieces excised from the body, reaggregates of dissociated single cells can also regenerate. Although the cellular events involved in the regeneration process have been well characterized, the underlying molecular mechanisms are yet to be uncovered. Recently, however, transcription factors and signaling molecules, both proteins and short peptides, have been identified and their role suggested in patterning and morphogenesis. In this article, a regeneration study at the tissue level is first described and then the importance of epithelial cells in regeneration is stressed. Finally, the recent study on morphogenetic peptides derived from epithelial cells is reviewed.

Animals↗
PubMed2003

Peduncle of Hydra and the heart of higher organisms share a common ancestral origin.

The heart is assumed to have evolved as the organ for pumping blood. Here we report a pumping phenomenon in Hydra, a member of the phylum Cnidaria. We find that the peduncle, lower quarter of the body column, stores most of the gastrovascular fluid when the animal is an elongate form. Upon contraction of the polyp, the peduncle contracts and transfers the fluid into the rest of the cavity. We also find that Hydra RFamide III, a homolog of cardioexcitatory RFamide neuropeptides in higher organisms, elevates this transfer activity. Further, CnNk-2, a homolog of a cardiomuscular tissue marker Nkx-2.5, is expressed in the endodermal tissue of the peduncle. These observations indicate that the transfer of fluid by the peduncle has a similar neurological and genetic basis to the pumping of blood by the heart, suggesting that the Hydra peduncle and the heart of higher organisms share a common ancestral origin.

Animals↗
PubMed2003

Identification of a new member of the GLWamide peptide family: physiological activity and cellular localization in cnidarian polyps.

KPNAYKGKLPIGLWamide, a novel member of the GLWamide peptide family, was isolated from Hydra magnipapillata. The purification was monitored with a bioassay: contraction of the retractor muscle of a sea anemone, Anthopleura fuscoviridis. The new peptide, termed Hym-370, is longer than the other GLWamides previously isolated from H. magnipapillata and another sea anemone, A. elegantissima. The amino acid sequence of Hym-370 is six residues longer at its N-terminal than a putative sequence previously deduced from the cDNA encoding the precursor protein. The new longer isoform, like the shorter GLWamides, evoked concentration-dependent muscle contractions in both H. magnipapillata and A. fuscoviridis. In contrast, Hym-248, one of the shorter GLWamide peptides, specifically induced contraction of the endodermal muscles in H. magnipapillata. This is the first case in which a member of the hydra GLWamide family (Hym-GLWamides) has exhibited an activity not shared by the others. Polyclonal antibodies were raised to the common C-terminal tripeptide GLWamide and were used in immunohistochemistry to localize the GLWamides in the tissue of two species of hydra, H. magnipapillata and H. oligactis, and one species of sea anemone, A. fuscoviridis. In each case, nerve cells were specifically labeled. These results suggest that the GLWamides are ubiquitous among cnidarians and are involved in regulating the excitability of specific muscles.

Amides↗
PubMed2002

Analysis of a piwi-related gene implicates small RNAs in genome rearrangement in tetrahymena.

During development of the somatic macronucleus from the germline micronucleus in ciliates, chromosome rearrangements occur in which specific regions of DNA are eliminated and flanking regions are healed, either by religation or construction of telomeres. We identified a gene, TWI1, in Tetrahymena thermophila that is homologous to piwi and is required for DNA elimination. We also found that small RNAs were specifically expressed prior to chromosome rearrangement during conjugation. These RNAs were not observed in TWI1 knockout cells and required PDD1, another gene required for rearrangement, for expression. We propose that these small RNAs function to specify sequences to be eliminated by a mechanism similar to RNA-mediated gene silencing.

Animals↗