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Y Kobayakawa

Publications and source records attributed to Y Kobayakawa.

16 recordsLinked to original sources
PubMed2000

Dorsal induction from dorsal vegetal cells in Xenopus occurs after mid-blastula transition.

We performed some experiments to investigate the temporal and spatial details of the dorsal induction exerted by dorsal vegetal cells in Xenopus embryo. Two dorsal vegetal cells (D1 cells) were transplanted into the ventral vegetal region of a recipient at the 32-cell stage. At various times after transplantation, the ventral animal-equatorial part was explanted and cultured. The explants isolated 5.5 h after transplantation (time 5.5) elongated and formed somites. In RT-PCR analysis, the expression of dorsal gene, chordin was activated in the explants isolated after time 4.0 (about the 4000-cell stage which corresponds to the mid blastula transition (MBT)) at control stage 10. In another series of experiments, ventral animal-equatorial and dorsal vegetal parts were isolated from the 4000-cell stage embryos and they were combined for 2.0-2.5 h. These ventral animal-equatorial explants elongated and formed somites. The chordin expression was also observed in the explants. But the 32- and 256-cell stage dorsal vegetal cells failed to exert the dorsalizing activity within the 2.0-2.5 h of the conjugation. These results suggest that 2 h contact after MBT is necessary and sufficient for the dorsal induction from the dorsal vegetal cells and it occurs as a result of the zygotic gene expression. Consistent with this idea, the zygotic dorsal genes, siamois and chordin were expressed on the upper regions of the transplanted D1 descendants at stage 10. Furthermore, this region began to gastrulate when the D1 cell was transplanted with upside-down orientation. Our data indicate that the upper region of the D1 descendants by itself act as the Spemann organizer rather than the Nieuwkoop center.

Animals↗
PubMed2000

A novel neuropeptide, Hym-355, positively regulates neuron differentiation in Hydra.

During the course of a systematic screening of peptide signaling molecules in Hydra a novel peptide, Hym-355 (FPQSFLPRG-NH(2)), was identified. A cDNA encoding the peptide was isolated and characterized. Using both in situ hybridization and immunohistochemistry, Hym-355 was shown to be expressed in neurons and hence is a neuropeptide. The peptide was shown to specifically enhance neuron differentiation throughout the animal by inducing interstitial cells to enter the neuron pathway. Further, co-treatment with a PW peptide, which inhibits neuron differentiation, nullified the effects of both peptides, suggesting that they act in an antagonistic manner. This effect is discussed in terms of a feedback mechanism for maintaining the steady state neuron population in Hydra.

Amino Acid Sequence↗
PubMed1998

A novel neuropeptide, Hym-176, induces contraction of the ectodermal muscle in Hydra.

During the course of a systematic non-targeting screening of peptide signal molecules in Hydra, we identified a novel myoactive neuropeptide called Hym-176. The primary structure of Hym-176 was determined to be APFIFPGPKVamide. It specifically and reversibly induced contraction of the ectodermal muscle of the hydra body column in vivo. However, it had no effect on the ectodermal muscle of the tentacles. The structure-activity relationship analysis showed that the sequence of FIFPGPKVamide is a minimal requirement for the myoactivity. Removal of an amide group from the C-terminus completely abolished the activity. By using the antibody specific to Hym-176, the tissue localization of the peptide in hydra was determined immunohistochemically. The intense immunoreactivity was found in the peduncle nerve cells, indicating that Hym-176 is a neuropeptide.

Amino Acid Sequence↗
PubMed1997

Targeted expression of ced-3 and Ice induces programmed cell death in Drosophila.

CED-3 is a cysteine protease required for programmed cell death in the nematode, Caenorhabditis elegans, and shares a sequence similarity with mammalian ICE (interleukin-1beta converting enzyme) family proteases. Both CED-3 and ICE family proteases can induce programmed cell death in mammalian cells. Structural and functional similarities between CED-3 and ICE family proteases indicate that the mechanism of cell death is evolutionarily conserved, suggesting the presence of a similar mechanism involving CED-3/ICE-like proteases in Drosophila. Here we determined whether CED-3 or ICE functions to induce programmed cell death in Drosophila. We have generated transformant lines in which ced-3 or Ice is ectopically expressed using the GAL4-UAS system. Expression of CED-3 and ICE can elicit cell death in Drosophila and the cell death was blocked by coexpressing the p35 gene which encodes a viral inhibitor of CED-3/ICE proteases. Results support the idea that the mechanism of programmed cell death controlled by CED-3/ICE is conserved among widely divergent animal species including Drosophila, and the system described provides a tool to dissect cell death mechanism downstream of CED-3/ICE proteases.

Journal Article↗
PubMed1997

Cell ablation by ectopic expression of cell death genes, ced-3 and Ice, in Drosophila.

We have developed a system for killing specific cells in Drosophila using ectopic expression of cell death genes. CED-3 and ICE (caspase-1) are proteins required for programmed cell death in the nematode Caenorhabditis elegans and in mammals, respectively. Our previous study has shown that both ced-3 and Ice can elicit cell death in Drosophila. By expressing ced-3 or Ice in several kinds of cells using a GAL4-UAS system and examining the resulting morphological defects, we show that these abnormalities are thought to be caused by the action of ced-3 or Ice genes. As cells are killed by apoptosis in our system, we could eliminate the possibility of harmful effects on the neighboring cells. Our system provides an alternative and novel cell ablation method to elucidate mechanisms of cell differentiation and cell-cell interactions during development in Drosophila.

Animals↗
PubMed1996

Structure, development, and maintenance of the nerve net of the body column in Hydra.

The anatomy and developmental dynamics of the nerve net in the body column of Hydra viridissima were examined immunocytochemically with a monoclonal antibody (CC04) that recognizes an antigen in nerve cells and with an antiserum against vasopressin. CC04+ neuron cell bodies, their neurites, and vasopressin-like-immunoreactive (VLI+) neurites could be clearly visualized on whole-mount preparations. All neurites of the CC04+ neurons in the body column were VLI+. However, only half of the VLI+ neurites in the body column were CC04+. Immunocytochemical analysis of macerated preparations showed that half of the neurons in the gastric region of the body column were CC04+. These results suggest that most of the neurons in the gastric region are VLI+. The density of the VLI+ neurites was uniform along the entire length of the body column. The CC04+ neuron density in the gastric region remained constant at all stages of asexual development and during foot regeneration. After pulse-labeling with 5-bromo-2'-deoxyuridine (BrdU), CC04+ neurons with labeled nuclei appeared in the body column. We conclude that neuron density in the gastric region is maintained at a constant value by insertion of new neurons in parallel with continuous epithelial cell division.

Animals↗
PubMed1995

Expression and functional analyses of the Dxpa gene, the Drosophila homolog of the human excision repair gene XPA.

Xeroderma pigmentosum (XP) is a human hereditary disease characterized by a defect in DNA repair after exposure to ultraviolet light. Among the seven groups of XP, group A (XP-A) patients show the most severe deficiency in excision repair and a wide variety of cutaneous and neurological disorders. We have cloned homologs of the human XPA gene from chicken, Xenopus, and Drosophila, and sequence analysis revealed that these genes are highly conserved throughout evolution. Here, we report characterization of the Drosophila homolog of the human XPA gene (Dxpa). The Dxpa gene product shows DNA repair activities in an in vitro repair system, and Dxpa cDNA has been shown to complement a mutant allele of human XP-A cells by transfection. Polytene chromosome in situ hybridization mapped Dxpa to 3F6-8 on the X chromosome, where no mutant defective in excision repair was reported. Northern blot analysis showed that the gene is continuously expressed in all stages of fly development. Interestingly, the Dxpa protein is strongly expressed in the central nervous system and muscles as revealed by immunohistochemical analysis using anti-Dxpa antibodies, consistent with the results obtained in transgenic flies expressing a Dxpa-beta-galactosidase fusion gene driven by the Dxpa promoter.

Amino Acid Sequence↗
PubMed1995

Suppressor of hairless, the Drosophila homologue of RBP-J kappa, transactivates the neurogenic gene E(spl)m8.

Suppressor of Hairless[Su(H)], the Drosophila homologue of RBP-J kappa is a novel type of sequence-specific DNA binding protein without known motifs, and highly conserved in various organisms. Su(H) regulates peripheral nervous system (PNS) development. Recently Su(H) was suggested to participate in the Notch-mediated signal transduction pathway. We show here that the Su(H) protein binds to TGTGGGAA sequence located 616 base-pairs upstream of the transcription initiation site of the Enhancer of split [E(spl)]m8 gene which is mapped to the terminus of the genetic cascade of the neurogenic genes. Su(H) transactivates the E(spl)m8 promoter not only in cultured Drosophila cells but also in vivo. The present study bridges the biochemical gap between Notch and E(spl) in the neurogenic gene cascade including Delta, Notch, deltex, Su(H), Hairless and E(spl).

Alleles↗
PubMed1994

The function of argos in regulating cell fate decisions during Drosophila eye and wing vein development.

The Drosophila argos gene, which encodes a secreted protein with an EGF motif, is involved in several developmental processes regulating cell-cell interactions such as eye morphogenesis. Loss-of-function mutations in the argos gene cause an increase in the number of photoreceptor cells and cone cells, impaired retinal projections to the optic lobe, and the formation of extra veins. We show here that ubiquitously expressed argos product restored all these loss-of-function phenotypes. Overexpression of argos in the wild-type background resulted in the reduced number of photoreceptor cells, cone cells, and pigment cells, which are phenotypes opposite to those of the loss-of-function mutants. The argos gene is expressed in developing wing veins. Ubiquitous argos expression caused loss of veins in a dose-dependent manner. This phenotype was enhanced by the loss-of-function rhomboid mutation, implying the possibility that argos and rhomboid play key roles in a common pathway for normal wing vein formation. We propose that argos acts as an inhibitory signal for cellular differentiation in the developing eye and wing.

Animals↗
PubMed1994

Genetic characterization of Drosophila RBP-J kappa (suppressor of hairless) as a neurogenic gene in adult PNS development.

Drosophila RBP-J kappa is a novel sequence-specific DNA binding protein encompassing the integrase motif which is highly conserved in various organisms. Its gene has been shown to be identical to Suppressor of Hairless which regulates adult peripheral nervous system (PNS) development. To elucidate the precise function of the RBP-J kappa protein in adult PNS development, we analyzed transgenic files that misexpress the RBP-J kappa protein. Such studies have shown that RBP-J kappa regulates PNS cell fate in at least two steps: commitment to sensory mother cell by lateral inhibition and terminal differentiation into the socket and shaft cells. Taken together with analysis of phenotypes of Suppressor of Hairless mutants, RBP-J kappa shows the synergistic activity with neurogenic genes.

Animals↗
PubMed1990

A cytoplasmic determinant for dorsal axis formation in an early embryo of Xenopus laevis.

In Xenopus laevis, dorsal cells that arise at the future dorsal side of an early cleaving embryo have already acquired the ability to cause axis formation. Since the distribution of cytoplasmic components is markedly heterogeneous in an egg and embryo, it has been supposed that the dorsal cells are endowed with the activity to form axial structures by inheriting a unique cytoplasmic component or components localized in the dorsal region of an egg or embryo. However, there has been no direct evidence for this. To examine the activity of the cytoplasm of dorsal cells, we injected cytoplasm (dorsal cytoplasm) from dorsal vegetal cells of a Xenopus 16-cell embryo into ventral vegetal cells of a simultaneous recipient. The cytoplasm caused secondary axis formation in 42% of recipients. Histological examination revealed that well-developed secondary axes included notochord, as well as a neural tube and somites. However, injection of cytoplasm of ventral vegetal cells never caused secondary axis and most recipients became normal tailbud embryos. Furthermore, about two-thirds of ventral isolated halves injected with dorsal cytoplasm formed axial structures. These results show that dorsal, but not ventral, cytoplasm contains the component or components responsible for axis formation. This can be the first step towards identifying the molecular basis of dorsal axis formation.

Animals↗
PubMed1985

Accumulation of pigment granules around nuclei in early embryos of Anura (Amphibia).

A dark spot was found to appear in each blastomere of the vegetal surface of blastulae of Rana rugosa, Hyla arborea. The spot divided into two before division of the blastomere, so that one new spot was allotted to each daughter cell. These dark spots were formed at early blastula stage, and persisted until the end of yolk plug stage. Cytological observations showed that each dark spot corresponds to a mass of accumulated pigment granules around the nucleus of a blastomere. The accumulation increases with development during the cleavage period more rapidly in blastomeres of the vegetal hemisphere than in those of the animal hemisphere. This accumulation of pigment granules around nuclei during development indicates that the granules are transported toward the nuclei during the cleavage period, suggesting some sort of directional flow of cytoplasm in blastomeres of early amphibian embryos.

Animals↗
PubMed1982

Surface contraction waves in amphibian eggs.

Circular waves of change in brightness, known as 'surface contraction waves' (SCW-1 and SCW-2), propagate over the animal surface of amphibian eggs at each cycle of cleavage. Movement of carbon particles attached to the egg surface indicated that SCW-1 involves expansion of the egg surface, whereas SCW-2 accompanies surface contraction. Stiffness of the cortex as measured by applying negative pressure through a micropipette increased concomitantly with the passage of SCW-2. Measurement of stiffness at two loci on the egg surface with two sets of pipettes confirmed the spatio-temporal coincidence of the wave of stiffness and SCW-2. The stiffness showed either no change or even a slight decrease on passage of SCW-1. Thus SCW-2 is a genuine wave of 'contraction', but SCW-1 can more properly be called a 'surface relaxation wave'.

Animals↗
PubMed1981

Temporal pattern of cleavage and the onset of gastrulation in amphibian embryos developed from eggs with the reduced cytoplasm.

Fertilized eggs of the Japanese newt, Cynops pyrrhogaster, were divided into two or four equal-sized parts with fine glass rods before the first cleavage. In such cases one of the egg fragments, at least, proceeds to cleavage and gastrulates. The temporal pattern of cell division and the onset of gastrulation in such half or quarter embryos were investigated and compared with normal development. The following results were obtained: (1) desynchronization starts two divisions earlier in quarter embryos and one division earlier in half embryos compared with whole embryos, (2) the time from the first cleavage to the onset of gastrulation does not widely vary among quarter, half and whole embryos and (3) the numbers of blastomeres which constitute embryos at the pigment stage decrease in proportion to the diminution of egg volume.

Animals↗