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K Sawamoto

Publications and source records attributed to K Sawamoto.

35 records · Page 2Linked to original sources
PubMed1999

Musashi and seven in absentia downregulate Tramtrack through distinct mechanisms in Drosophila eye development.

We have examined the roles played by the Drosophila neural RNA-binding protein Musashi (MSI) in eye development. MSI expression was observed in the nuclei of all photoreceptor cells (R1-R8). Although a msi loss-of-function mutation resulted in only weak abnormalities in photoreceptor differentiation, we found that the msi eye phenotype was significantly enhanced in a seven in absentia (sina) background. sina is known to be involved in the degradation of the Tramtrack (TTK) protein, leading to the specification of the R7 fate. We demonstrated that MSI also functions to regulate TTK expression. The sina msi mutants showed significantly high ectopic expression of TTK69 and failure in the determination of the R1, R6, and R7 fates. Other photoreceptor cells also failed to differentiate with abnormalities occurring late in the differentiation process. These results suggest that MSI and SINA function redundantly to downregulate TTK in developing photoreceptor cells.

Animals↗
PubMed1999

Control of the cell death pathway by Dapaf-1, a Drosophila Apaf-1/CED-4-related caspase activator.

We identified a Drosophila Apaf-1/CED-4 homolog gene, dapaf-1. Alternative splicing results in two dapaf-1 mRNA species, which encode distinct forms of caspase activator, Dapaf-1L (Apaf-1 type) and Dapaf-1S (CED-4 type). Distinct caspases were activated by these Dapaf-1 isoforms. Loss of Dapaf-1 function resulted in defective cytochrome c-dependent caspase activities and reduced apoptosis in embryo and in larval brain. Dapaf-1 activities were also involved in cell death induced by ectopic expression of reaper in the compound eye. These data suggest that Dapaf-1/cytochrome c-dependent cell death-inducing machinery is present in Drosophila, and the requirement of Dapaf-1/Apaf-1 in neural cell death is conserved through evolution.

Alternative Splicing↗
PubMed1998

A novel Drosophila paired-like homeobox gene related to Caenorhabditis elegans unc-4 is expressed in subsets of postmitotic neurons and epidermal cells.

We have isolated a novel Drosophila paired-like homeobox gene, DPHD-1. The homeodomain of DPHD-1 showed 85% amino-acid identity with that of the C. elegans Unc-4 protein. Whole-mount in situ hybridization of embryos and third-instar larvae revealed that the DPHD-1 mRNA is specifically localized in subsets of postmitotic neurons in the central nervous system (CNS) and in the developing epidermis with a segmentally repeated pattern. Double staining with a posterior compartment marker, an anti-Engrailed antibody, showed that DPHD-1 expressing neurons in the CNS were present in the posterior compartment, whereas DPHD-1 expression in the epidermis was restricted to the anterior compartment in each segment. This temporal and spatial expression pattern suggests that DPHD-1 may play a role in determining the distinct cell types in each segment.

Amino Acid Sequence↗
PubMed1998

Mammalian BarH homologue is a potential regulator of neural bHLH genes.

Vertebrate neurogenesis involves sequential actions of transcription factors. neurogenins, encoding Atonal-related bHLH transcription factors, function as neuronal determination genes in Xenopus. neurogenins and antother bHLH factor gene, Mash1, are expressed in distinct subsets or areas of cells giving rise to neurons, suggesting that these genes play important roles to generate distinct populations of neurons. A mammalian homologue of BarH (MBH1) is expressed in a complementary pattern to Mash1 expression in the developing nervous system like neurogenins. Forced expression of MBH1 down-regulates expression of Mash1 and up-regulates neurogenin2/Math4A, a member of neurogenins, in P19 cells during neuronal differentiation. This suggests that MBH1 is a potential regulator of mammalian neural bHLH genes, thereby establishing distinct pathways of neuronal differentiation.

Amino Acid Sequence↗
PubMed1998

Argos induces programmed cell death in the developing Drosophila eye by inhibition of the Ras pathway.

We studied the role of Ras signaling in the regulation of cell death during Drosophila eye development. Overexpression of Argos, a diffusible inhibitor of the EGF receptor and Ras signaling, caused excessive cell death in developing eyes at pupal stages. The Argos-induced cell death was suppressed by coexpression of the anti-apoptotic genes p35, diap1, or diap2 in the eye as well as by the Df(3L)H99 chromosomal deletion that lacks three apoptosis-inducing genes, reaper, head involution defective (hid) and grim. Transient misexpression of the activated Ras1 protein (Ras1V12) later in pupal development suppressed the Argos-induced cell death. Thus, Argos-induced cell death seemed to have resulted from the suppression of the anti-apoptotic function of Ras. Conversely, cell death induced by overexpression of Hid was suppressed by gain-of-function mutations of the genes coding for MEK and ERK. These results support the idea that Ras signaling functions in two distinct processes during eye development, first triggering the recruitment of cells and later negatively regulating cell death.

Animals↗
PubMed1997

Intrinsic and extrinsic determinants regulating cell fate decision in developing nervous system.

Cell fate in the nervous system is determined by environmental signals and/or heredity. They can be referred to as extrinsic and intrinsic determinants, respectively. The molecular and cellular mechanisms underlying these processes are well conserved from invertebrates to vertebrates. We have identified both types of determinants through the intensive screening of P-element-induced Drosophila mutants affected in neural development. As a member of the first category, argos gene product which regulates cell-cell interaction in the developing nervous system gives a good example. As a member of the second category, we refer to Drosophila musashi gene encoding a neural RNA-binding protein. The fractions of these gene products and application to the mammalian nervous system will be discussed.

Animals↗
PubMed1997

Evolutionarily conserved mechanisms regulating neural development: lessons from the development of Drosophila peripheral nervous systems.

Functions of genes regulating the development of Drosophila peripheral nervous systems are summarized herein. These genes can be classified into 6 groups: <1> prepattern genes, <2> proneural genes, <3> neurogenic genes, <4> neuronal precursor genes, <5> neuronal precursor type selector genes, and <6> cell-division and lineage genes. The mechanisms described herein provide excellent paradigms in the regulation of the development of other tissues in Drosophila, as well as in other organisms, including vertebrates. The roles of two different inhibitory mechanisms, i.e. Notch-signaling and Argos, in the development of Drosophila neural precursor cells are also discussed.

Animals↗
PubMed1996

The Drosophila secreted protein Argos regulates signal transduction in the Ras/MAPK pathway.

The Drosophila argos gene encodes a secreted protein with an EGF motif which acts as an inhibitor of cellular differentiation in multiple developmental processes. To investigate the cellular pathways regulated by Argos, we screened for mutations which could modify the phenotype caused by overexpression of argos. We show that the effects of argos overexpression on the eye and wing vein development are suppressed by gain-of-function mutations of the MAPKK/D-MEK gene (Dsor1/D-mek) and the MAPK/ERK-A gene (rolled) and were enhanced by loss-of-function mutations of Star. Loss-of-function mutations in components of the Ras/MAPK signaling cascade act as dominant suppressors of the phenotype caused by the argos null mutations. A loss-of-function argos mutation enhanced the overproduction of R7 neurons caused by gain-of-function alleles of Son of sevenless and Dsor1. Conversely, overexpression of argos inhibited formation of the extra R7 cells that was caused by high-level MAPK/ERK-A activity. A phenotype of the sev; argos double mutants revealed that sev is epistatic to argos. These results provide evidence that Argos negatively regulates signal transduction events in the Ras/MAPK cascade.

Animals↗
PubMed1996

The function of the Drosophila argos gene product in the development of embryonic chordotonal organs.

We characterized the embryonic expression pattern and mutant phenotypes of the Drosophila gene argos, which encodes a secreted protein with an epidermal growth factor motif. The argos null mutation caused an increase in chordotonal (Ch) organs in both the thoracic and the abdominal segments, whereas overexpression of the argos gene resulted in a decrease in these organs. We showed that the argos transcripts are expressed transiently in the cells surrounding the Ch organ precursor and that the gene rhomboid (rho), which is involved in the regulation of the number of Ch organs, acts epistatically to argos in this event. Our findings suggest that argos plays a role in Ch organ precursor formation and regulates the final number of Ch organs.

Abdomen↗
PubMed1996

argos Is required for projection of photoreceptor axons during optic lobe development in Drosophila.

The Drosophila argos gene encodes a secreted protein with an epidermal growth factor (EGF) motif, which acts as an inhibitor of cell recruitment in the developing eye and wing. Here, we have analyzed the role of argos during optic lobe development. argos expression was observed in the optic lobes throughout the developmental stages. In argos mutants, neuropiles failed to develop normally during embryonic and larval stages, and photoreceptor axons did not project properly into the lamina. Ubiquitous expression of argos, under control of the hsp70 promoter, rescued the defects in optic lobes. We have found that glial cells failed to differentiate in the larval optic lobes of argos mutants. Correspondingly, in loss-of-function repo mutants, whose glial cells also fail to differentiate, photoreceptor axons showed the impaired projection pattern similar to the argos phenotype. These results suggest that glial cells play a role for guidance of photoreceptor axons. The loss-of-function Star mutation (StarX155) dominantly suppressed the defects in the argos optic lobes, suggesting that these two genes act in an antagonistic fashion during optic lobe development.

Animals↗
PubMed1996

Cell-cell interactions during neural development: multiple types of lateral inhibitions involved in Drosophila eye development.

Inhibitory signals of cellular differentiation from differentiating cells play an important role in regulating the number and spatial distribution of distinctive types of cells in developing tissues. Several types of inhibitory mechanisms of cellular differentiation have been identified by making full use of the developmental genetics of Drosophila compound eyes. These inhibitory mechanisms are distinct from each other in their signal transduction cascades and/or their role in the pattern formation of the developing Drosophila eye. The following events occur: firstly a diffusible protein, Scabrous (Sca), is required to confer regular spacings of the founder cells, R8 cells, or preommatidial clusters in the developing eye disc via an unknown signal transduction cascade, secondly the Notch-signalling is at least required for the single-out of the R8 cells within the pre-ommatidial cluster possibly by preventing other cells in the equivalent groups from adapting fates as R8 cells. Notch-signalling activates a simple signal cascade mediating communication between the plasma membrane and nucleus not via protein phosphorylation. In contrast, a novel diffusible ligand, Argos, was likely to be required subsequently to the selection of R8 cells. Argos was shown to inhibit the activation of a receptor tyrosine kinase, DER, and the subsequent signal transduction in the Ras/MAPK cascade (the third inhibitory mechanism). We proposed that the role of Argos is to regulate the number of differentiated cells by controlling cellular differentiation and subsequent programmed cell death. The distinct roles of these inhibitory signals in the developing Drosophila eye are discussed in detail.

Animals↗
PubMed1995

Changes in the organelle arrangement in primary cultured hepatocytes following the formation of cytoskeleton.

The relationship between the arrangement of organelles and cytoskeleton in primary cultured hepatocytes was studied morphologically by using fluorescent dyes. Double staining with DiOC6(3) and rhodamine-conjugated phalloidin revealed that the distribution of endoplasmic reticulum was identical with the distribution of F-actin in the marginal areas of well-spread hepatocytes. As the cells spread further, the mitochondria which were positively stained with rhodamine 123 began to show a radial distribution, extending from the centre of the cell towards its margins. This pattern was disturbed after the microtubules were depolymerized with colchicine. Simultaneous double staining using rhodamine-conjugated phalloidin and anti-tubulin antibody revealed that the distribution of stress fibres resembles that of microtubules in hepatocytes. These results suggest that the arrangement of organelles in hepatocytes is determined by the cytoskeleton.

Actins↗
PubMed1994

Cloning of a Drosophila melanogaster homologue of the mouse type-I bone morphogenetic proteins-2/-4 receptor: a potential decapentaplegic receptor.

The Drosophila melanogaster (Dm) decapentaplegic (dpp) gene product plays an essential role during several stages of Dm development. The DPP protein is a member of the transforming growth factor-beta (TGF-beta) superfamily and an orthologue of mammalian bone morphogenetic proteins (BMP-2 and -4). Recently, a cDNA clone encoding the mouse Ser/Thr kinase receptor specific for BMP-2/-4 (mTFR11) was isolated. Here, we describe the deduced primary structure, the cytogenetic position and expression pattern of the Dm homologue of mTFR11 (DTFR), a putative DPP receptor. The cytogenetic position of the Dm dtfr gene was mapped to 25D. DTFR has striking homology to mTFR11, especially in the cytoplasmic domain (approx. 63%), including a Ser + Gly-rich box that is characteristic of type-I receptors for the TGF-beta superfamily. Although the amino acid (aa) sequence of the extracellular domain is less conserved than that of the cytoplasmic domain, the extracellular domains of these two molecules were more homologous (approx. 27%) to each other than any other receptors for the TGF-beta superfamily. The spacing of Cys residues in the extracellular domain, which is considered crucial to ligand specificity, is highly conserved in these two receptors. During Dm embryonic development, its expression pattern changes in a dynamic fashion with high levels of expression in mesoderm and midgut, with some relation to dpp mutant phenotypes.

Amino Acid Sequence↗
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↗
PubMed1992

Regulation of Drosophila neural development by a putative secreted protein.

The Drosophila strawberry (sty) locus was isolated by P-element insertion mutagenesis in a screen for mutations affecting eye development. Analysis of the mutant phenotype and the putative expression pattern of the sty gene suggested that it has multiple functions. Mutations in the sty gene lead to irregular spacing of ommatidia, an increase in the number of photoreceptor cells, as well as abnormal axonal projections to the lamina and disrupted structure of the optic lobes in the adult fly. The sty mutation also causes abnormal head involution, a change in a number of sensilla in the antennomaxillary complex in the embryonic stage and abnormal morphogenesis of the maxillary palp and wings in later stages. We examined the presumptive expression of the sty gene during development by histochemical staining for lacZ expression from enhancer trap elements inserted within the sty gene. During embryogenesis, expression of lacZ showed a segmental pattern in the ectoderm and in the nervous system. In the eye imaginal discs, lacZ was expressed in photoreceptor cells beginning a few rows posterior to the morphogenetic furrow. The lacZ was also expressed in the wing disc. In the adult, lacZ was expressed in the retina and lamina. We cloned the sty gene by P-element tagging and found that it encodes a putative secreted protein containing a cysteine-rich region similar to the epidermal growth factor (EGF) repeat. On the basis of the loss of functional phenotype, the expression pattern and the predicted structure of its product, we propose that sty encodes a diffusible protein acting as a signal involved in lateral inhibition within the developing nervous system and also as a factor involved either directly or indirectly in axonal guidance and optic lobe development.

Animals↗
PubMedDate not supplied

Modulation of hepatocyte function by changing the cell shape in primary culture.

To study the role of cell shape in control of hepatocyte function, we have developed a system that can quantitatively control the spreading of cultured rat hepatocytes using poly[2-hydroxyethyl methacrylate]. When hepatocytes were cultured in a dish coated with high concentration of poly[2-hydroxyethyl methacrylate] solution, formation of stress fibers were suppressed and they continued to have a compact shape. In the compact-shaped hepatocytes, the ability to induce tyrosine aminotransferase with dexamethasone remained high for longer periods of time, as compared to the hepatocytes that spread following culture in the polystyrene dish. Conversely, the hepatocytes showed more active DNA synthesis when they assumed a flat shape as a result of spreading. When the hepatocytes that had spread following long-term culture in the polystyrene dishes were treated with cytochalasin to induce depolymerization of F-actin, the ability of the cells to induce tyrosine aminotransferase upon stimulation with dexamethasone improved markedly. This effect was not altered by treatment with actinomycin D but was completely suppressed by cycloheximide, suggesting that microfilaments are involved in the post-transcriptional process of tyrosine aminotransferase induction. Thus, there is a possibility that F-actin rather than cell shape might regulate cellular function in primary cultured hepatocytes.

Actins↗