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3 results on '"Motohiro Homma"'

1. A novel gene, BENI is required for the convergent extension during Xenopus laevis gastrulation

Author

Tatsuo Michiue, Masafumi Inui, Makoto Asashima, Akimasa Fukui, Koji Okabayashi, and Motohiro Homma

Subjects
Brachyury, Indoles, animal structures, Morpholino, Genetic Vectors, Molecular Sequence Data, Oligonucleotides, Xenopus, Ectoderm, Xenopus Proteins, Xbra, Xenopus laevis, medicine, Animals, Amino Acid Sequence, Molecular Biology, In Situ Hybridization, Body Patterning, DNA Primers, Cell Nucleus, Activin-like signaling, Gene knockdown, Nuclear localization signal (NLS), Base Sequence, biology, Reverse Transcriptase Polymerase Chain Reaction, Convergent extension, Gene Expression Profiling, Gene Expression Regulation, Developmental, Galactosides, Gastrula, Sequence Analysis, DNA, Cell Biology, biology.organism_classification, Molecular biology, Activins, Gastrulation, medicine.anatomical_structure, BENI, embryonic structures, T-Box Domain Proteins, Signal Transduction, Developmental Biology
Abstract

Activin-like signaling plays an important role in early embryogenesis. Activin A, a TGF-β family protein, induces mesodermal/endodermal tissues in animal cap assays. In a screen for genes expressed early after treatment with activin A, we isolated a novel gene, denoted as BENI (Brachyury Expression Nuclear Inhibitor). The BENI protein has a conserved domain at the N-terminus that contains a nuclear localization signal (NLS), and two other NLSs in the C-terminal domain. BENI mRNA was localized to the animal hemisphere at the gastrula stages and to ectoderm except for neural regions at stage 17; expression persisted until the tadpole stage. The overexpression of BENI caused gastrulation defects and inhibition of elongation of activin-treated animal caps with reduction of Xbra expression. Moreover, whole-mount in situ hybridization revealed reduced expression of Xbra in BENI mRNA-injected regions of gastrula embryos. Functional knockdown of BENI using an antisense morpholino oligonucleotide also resulted in an abnormal phenotype of embryos curling to the dorsal side, and excessive elongation of activin-treated animal caps without altered expression of mesodermal markers. These results suggested that BENI expression is regulated by activin-like signaling, and that this regulation is crucial for Xbra expression.

Published
2007
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2. SDF-1 alpha regulates mesendodermal cell migration during frog gastrulation

Author

Makoto Asashima, Motohiro Homma, Akimasa Fukui, Junko Kitamoto, and Toshiyasu Goto

Subjects
Receptors, CXCR4, Polarity in embryogenesis, Biophysics, Xenopus, Biochemistry, Mesoderm, Xenopus laevis, Cell Movement, medicine, Animals, Molecular Biology, Genetics, biology, Blastocoel, Endoderm, breakpoint cluster region, Cell migration, Embryo, Cell Biology, Gastrula, biology.organism_classification, Chemokine CXCL12, Cell biology, Gastrulation, medicine.anatomical_structure, embryonic structures, Chemokines, CXC
Abstract

During frog gastrulation, mesendodermal cells become apposed to the blastocoel roof (BCR) by endoderm rotation, and migrate towards the animal pole. The leading edge of the mesendodermal cells (LEM) contributes to the directional migration of involuting marginal zone (IMZ) cells, but the molecular mechanism of this process is not well understood. Here we show that CXCR4/SDF-1 signaling mediates the directional movement of the LEM in Xenopus embryos. Expression of xCXCR4 was detected in the IMZ, and was complemented by xSDF-1α expression in the inner surface of the BCR. Over-expression of xCXCR4 and xSDF-1α caused gastrulation defects. An xCXCR4 N-terminus deletion construct and xSDF-1α-MO also inhibited gastrulation. Furthermore, explants of LEM migrate towards the dorsal BCR in the presence of xSDF-1α , and altered xCXCR4 expression in the LEM inhibited LEM migration. These results suggest that CXCR4/SDF-1 signaling is necessary for the migrations of massive numbers of cells during gastrulation.

Published
2006

3. Attractant binding alters arrangements of Chemoreceptor dimers within its cluster at a cell pole.

Author

Motohiro Homma, Peter G., Daisuke Shiomi, Peter G., Michio Homma, Peter G., and Ikuro Kawagishi, Peter G.

Subjects
*PROTEIN binding, *CHEMORECEPTORS, *DIMERS, *SENSE organs, *OLIGOMERS, *BIOCHEMISTRY
Abstract

Many sensory systems involve multiple steps of Signal amplification to produce a significant response. One such mechanism may be the clustering of transmembrane receptors. In bacterial chemotaxis, where astoichiometric His-Asp phosphorelay from the kinase CheA to the response regulator CheY plays a central role, the chemoreceptors (methyl-accepting chemotaxis proteins) cluster together with CheA and the adaptor CheW, at a pole of a rod-shaped cell. This clustering led to a proposal that signal amplification occurs through an interaction between chemoreceptor homodimers. Here, by using in vivo disulfide cross-linking assays, we examined an inter-dimer interaction of the aspartate chemoreceptor (Tar). Two cysteine residues were introduced into Tar: one at the subunit interface and the other at the external surface of the dimer. Crosslinked dimers and higher oligomers (especially a deduced hexamer) were detected and their abundance depended on CheA and CheW. The ligand aspartate significantly reduced the amounts of higher oligomers but did not affect the polar localization of Tar-GFP. Thus, the binding of aspartate alters the rate of collisions between tar dimers in assembled signaling complexes, most likely due to a change in the relative positions or trajectories of the dimers. These collisions could occur within a trimer-of-dimers predicted by crystallography, or between such timers. These results are consistent with the proposal that the interaction of chemoreceptor dimers is involved in signal transduction. [ABSTRACT FROM AUTHOR]

Published
2004
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