PubMed Health⌕ Search

Biomedical subjects

Masahiko Hibi

Publications and source records attributed to Masahiko Hibi.

8 recordsLinked to original sources
PubMed2003

Gab1 is required for EGF receptor signaling and the transformation by activated ErbB2.

Grb2-associated binder-1 (Gab1) is a pleckstrin homology (PH) domain-containing adapter molecule that is believed to function downstream of receptors for growth factors and cytokines. We previously found that deficiency in the mouse Gab1 gene led to embryonic lethality and defects in ERK activation in response to growth factors and cytokines. Here, we established immortalized Gab1-/- cell lines and analysed roles of Gab1 in growth factor-mediated signaling and oncogenesis. EGF-dependent activation of c-Raf and Mek1/2, which function upstream of ERKs, was perturbed in Gab1-/- cells. EGF-mediated upregulation of GTP-bound form of Ras was also reduced in these cells. EGF-dependent GTP/GDP exchange activity for Ras was suppressed in the Gab1-/- cells and expression of a constitutively active Sos restored ERK activation in these cells, indicating that Gab1 functions upstream of Ras. Furthermore, activated form of ErbB2 (active ErbB2)-mediated transformation, such as colony formation in soft agar and tumor formation in nude mice, was strongly suppressed when the Gab1-/- cells were transfected with active ErbB2, whereas the active Sos efficiently induced transformation of Gab1-/- cells. The data show that Gab1 plays an essential role in EGF-receptor/ErbB-mediated cell proliferation and oncogenesis.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Zinc finger protein too few controls the development of monoaminergic neurons.

The mechanism controlling the development of dopaminergic (DA) and serotonergic (5HT) neurons in vertebrates is not well understood. Here we characterized a zebrafish mutant--too few (tof)--that develops hindbrain 5HT and noradrenergic neurons, but does not develop hypothalamic DA and 5HT neurons. tof encodes a forebrain-specific zinc finger transcription repressor that is homologous to the mammalian Fezl (forebrain embryonic zinc finger-like protein). Mosaic and co-staining analyses showed that fezl was not expressed in DA or 5HT neurons and instead controlled development of these neurons non-cell-autonomously. Both the eh1-related repressor motif and the second zinc finger domain were necessary for tof function. Our results indicate that tof/fezl is a key component in regulating the development of monoaminergic neurons in the vertebrate brain.

Animals↗
PubMed2003

A homeobox gene, pnx, is involved in the formation of posterior neurons in zebrafish.

A homeobox gene, pnx, is expressed in prospective posterior neurogenic regions and later in primary neurons. pnx expression was regulated by a signal from the non-axial mesendoderm and by Notch signaling. Pnx contains an Eh1 repressor domain, which interacted with Groucho and acted as a transcriptional repressor. Misexpression of pnx increased neural precursor cells and postmitotic neurons, which express neurogenin1 and elavl3/HuC, respectively. Expression of an antimorphic Pnx (VP16Pnx) or inhibition of Pnx by antisense morpholino oligonucleotide led to the reduction in the number of a subset of primary neurons. Misexpression of pnx promoted neurogenesis independent of Notch signaling. Epistatic analyses showed that Pnx also functions downstream of the Notch signal. These data indicate that pnx is a novel repressor-type homeobox gene that regulates posterior neurogenesis.

Amino Acid Sequence↗
PubMed2003

Ogon/Secreted Frizzled functions as a negative feedback regulator of Bmp signaling.

The zebrafish mutant ogon (also called mercedes and short tail) displays ventralized phenotypes similar to the chordino (dino) mutant, in which the gene for the Bmp antagonist Chordin is mutated. We isolated the gene responsible for ogon by a positional cloning strategy and found that the ogon locus encodes a zebrafish homolog of Secreted Frizzled (Sizzled), which has sequence similarity to a Wnt receptor, Frizzled. Unlike other secreted Frizzled-related proteins (sFrps) and the Wnt inhibitor Dickkopf1, the misexpression of Ogon/Sizzled dorsalized, but did not anteriorize, the embryos, suggesting a role for Ogon/Sizzled in Bmp inhibition. Ogon/Sizzled did not inhibit a Wnt8-dependent transcription in the zebrafish embryo. ogon/sizzled was expressed on the ventral side from the late blastula through the gastrula stages. The ventral ogon/sizzled expression in the gastrula stage was reduced or absent in the swirl/bmp2b mutants but expanded in the chordino mutants. Misexpression of ogon/sizzled did not dorsalize the chordino mutants, suggesting that Ogon/Sizzled required Chordin protein for dorsalization and Bmp inhibition. These data indicate that Ogon/Sizzled functions as a negative regulator of Bmp signaling and reveal a novel role for a sFrp in dorsoventral patterning.

Amino Acid Sequence↗
PubMed2002

Adapter molecule Grb2-associated binder 1 is specifically expressed in marginal zone B cells and negatively regulates thymus-independent antigen-2 responses.

Grb2-associated binder 1 (Gab1) is a member of the Gab/daughter of sevenless family of adapter molecules involved in the signal transduction pathways of a variety of growth factors, cytokines, and Ag receptors. To know the role for Gab1 in hematopoiesis and immune responses in vivo, we analyzed radiation chimeras reconstituted with fetal liver (FL) cells of Gab1(-/-) mice, because Gab1(-/-) mice are lethal to embryos. Transfer of Gab1(-/-) FL cells of 14.5 days post-coitum rescued lethally irradiated mice, indicating that Gab1 is not essential for hematopoiesis. Although mature T and B cell subsets developed normally in the peripheral lymphoid organs, reduction of pre-B cells and increase of myeloid cells in the Gab1(-/-) FL chimeras suggested the regulatory roles for Gab1 in hematopoiesis. The chimera showed augmented IgM and IgG1 production to thymus-independent (TI)-2 Ag, although they showed normal responses for thymus-dependent and TI-1 Ags, indicating its negative role specific to TI-2 response. Gab1(-/-) splenic B cells stimulated with anti-delta-dextran plus IL-4 plus IL-5 showed augmented IgM and IgG1 production in vitro that was corrected by the retrovirus-mediated transfection of the wild-type Gab1 gene, clearly demonstrating the cell-autonomous, negative role of Gab1. Furthermore, we showed that the negative role of Gab1 required its Src homology 2-containing tyrosine phosphatase-2 binding sites. Cell fractionation analysis revealed that nonfollicular B cells were responsible for the augmented Ab production in vitro. Consistent with these results, the Gab1 gene was expressed in marginal zone B cells but not follicular B cells. These results indicated that Gab1 is a unique negative regulator specific for TI-2 responses.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Requirement of Gab2 for mast cell development and KitL/c-Kit signaling.

Mast cells are thought to participate in a variety of immune responses, such as parasite resistance and the allergic reaction. Mast cell development depends on stem cell factor (Kit ligand) and its receptor, c-Kit. Gab2 is an adaptor molecule containing a pleckstrin homology domain and potential binding sites for SH2 and SH3 domains. Gab2 is phosphorylated on tyrosine after stimulation with cytokines and growth factors, including KitL. Gab2-deficient mice were created to define the physiological requirement for Gab2 in KitL/c-Kit signaling and mast cell development. In Gab2-deficient mice, the number of mast cells was reduced markedly in the stomach and less severely in the skin. Bone marrow-derived mast cells (BMMCs) from the Gab2-deficient mice grew poorly in response to KitL. KitL-induced ERK MAP kinase and Akt activation were impaired in Gab2-deficient BMMCs. These data indicate that Gab2 is required for mast cell development and KitL/c-Kit signaling.

Adaptor Proteins, Signal Transducing↗
PubMed2002

A novel repressor-type homeobox gene, ved, is involved in dharma/bozozok-mediated dorsal organizer formation in zebrafish.

Dharma/Bozozok (Dha/Boz) is a homeodomain protein containing an Engrailed homology (Eh) 1 repressor motif. It is important in zebrafish dorsal organizer formation. Dha/Boz interacted with a co-repressor Groucho through the Eh1 motif. Expression of a Dha/Boz fused to the transcriptional activator VP16 repressed dorsal axis formation and the expression of organizer genes but led to the dorsal expansion of expression of the homeobox gene vox/vega1, indicating that Dha/Boz functions as a transcriptional repressor for dorsal axis formation. We also isolated a novel homeobox gene, ved, whose expression was negatively regulated by dha/boz. ved's sequence and expression profile were similar to those of vox/vega1 and vent/vega2. Like Vox/Vega1 and Vent/Vega2, Ved acted as a transcriptional repressor. The combined inhibition of ved, vox/vega1, and vent/vega2, by antisense morpholino injection, strongly dorsalized the embryos and elicited ventral expansion of organizer gene expression, compared with the effect of inhibiting each of these genes alone. These results suggest that ved is a target for the repressor Dha/Boz. Ved functions redundantly with vox/vega1 and vent/vega2 to restrict the organizer domain.

Amino Acid Motifs↗