Shoko Yoshida

Identification of heterologous translocation partner genes fused to the BCL6 gene in diffuse large B-cell lymphomas: 5′-RACE and LA – PCR analyses of biopsy samples

In order to elucidate the molecular mechanism(s) for BCL6 translocation, we identified translocational partner genes by subjecting clinical biopsy samples from patients with non-Hodgkins lymphoma to 5′-rapid amplification of cDNA ends (5′-RACE). Sequence analysis of the 5′-RACE product revealed that the BCL6 gene was fused to the J segment of the immunoglobulin heavy chain (IgH) gene in about half of the cases, but in the other half, it was fused to heterologous partners, including the MHC class II transactivator (CIITA), pim-1, eukaryotic initiation factor 4AII (eif4AII), transferrin receptor (TFRR) and ikaros genes. Since analyses using genomic long and accurate (LA) – PCR revealed that the breakpoints in the partner gene were confined to the first intron or the second exon in all cases, the promoter and the first exon of the BCL6 gene were replaced by the promoter and the first or both the first and second exon of the partner gene. The breakpoint flanking sequences had no recombination signal sequences (RSSs) or chi sequences and were homologous with the switch region only when the BCL6 gene was fused to the IgH gene, suggesting that BCL6 translocation cannot be explained solely by mistakes of V(D)J, or chi-mediated or class-switch recombination, but rather another mechanism may also be required to explain the molecular mechanism for the promiscuous BCL6 translocation.

DPP signaling controls development of the lamina glia required for retinal axon targeting in the visual system of Drosophila

The Drosophila visual system consists of the compound eyes and the optic ganglia in the brain. Among the eight photoreceptor (R) neurons, axons from the R1-R6 neurons stop between two layers of glial cells in the lamina, the most superficial ganglion in the optic lobe. Although it has been suggested that the lamina glia serve as intermediate targets of R axons, little is known about the mechanisms by which these cells develop. We show that DPP signaling plays a key role in this process. dpp is expressed at the margin of the lamina target region, where glial precursors reside. The generation of clones mutant for Medea, the DPP signal transducer, or inhibition of DPP signaling in this region resulted in defects in R neuron projection patterns and in the lamina morphology, which was caused by defects in the differentiation of the lamina glial cells. glial cells missing/glial cells deficient (gcm; also known as glide) is expressed shortly after glia precursors start to differentiate and migrate. Its expression depends on DPP; gcm is reduced or absent in dpp mutants or Medea clones, and ectopic activation of DPP signaling induces ectopic expression of gcm and REPO. In addition, R axon projections and lamina glia development were impaired by the expression of a dominant-negative form of gcm, suggesting that gcm indeed controls the differentiation of lamina glial cells. These results suggest that DPP signaling mediates the maturation of the lamina glia required for the correct R axon projection pattern by controlling the expression of gcm.

Focal adhesion kinase controls morphogenesis of the Drosophila optic stalk

Photoreceptor cell axons (R axons) innervate optic ganglia in the Drosophila brain through the tubular optic stalk. This structure consists of surface glia (SG) and forms independently of R axon projection. In a screen for genes involved in optic stalk formation, we identified Fak56D encoding a Drosophila homolog of mammalian focal adhesion kinase (FAK). FAK is a main component of the focal adhesion signaling that regulates various cellular events, including cell migration and morphology. We show that Fak56D mutation causes severe disruption of the optic stalk structure. These phenotypes were completely rescued by Fak56D transgene expression in the SG cells but not in photoreceptor cells. Moreover, Fak56D genetically interacts with myospheroid, which encodes an integrin β subunit. In addition, we found that CdGAPr is also required for optic stalk formation and genetically interacts with Fak56D. CdGAPr encodes a GTPase-activating domain that is homologous to that of mammalian CdGAP, which functions in focal adhesion signaling. Hence the optic stalk is a simple monolayered structure that can serve as an ideal system for studying glial cell morphogenesis and the developmental role(s) of focal adhesion signaling.

Muscle determinants in the ascidian egg are inactivated by UV irradiation and the inactivation is partially rescued by injection of maternal mRNAs

The ascidian egg contains cytoplasmic determinants that specify the fate of larval muscle cells. In a previous study, we developed an experimental system to identify the molecular nature of muscle determinants, in which unfertilized Ciona savignyi eggs were fragmented into four pieces by centrifugation. When inseminated, only nucleated fragments (red fragments) develop into partial embryos that only show differentiation of epidermal cells. One type of enucleated fragment (black fragment) has the remarkable ability to promote muscle differentiation when fused with red fragments. In the present study, using this experimental system, we investigated the molecular nature of muscle determinants. UV irradiation of black fragments suppressed the ability to promote expression of the muscle-specific protein, myosin heavy chain. The wavelength of UV light responsible for the inactivation (250–275 nm) suggested that UV-sensitive targets are nucleic acids. Injection of poly(A)+ RNA isolated from an un-irradiated black-fragment-rich fraction into UV-irradiated black fragments partially recovered the ability to promote the expression of myosin heavy chain protein. Poly(A)+ RNA from a red-fragment-rich fraction did not rescue the suppression of UV-irradiated black fragments. These results suggest that maternal mRNAs enriched in black fragments are closely associated with muscle determinants in the ascidian egg.

PKA-R1 spatially restricts Oskar expression for Drosophila embryonic patterning

Targeting proteins to specific domains within the cell is central to the generation of polarity, which underlies many processes including cell fate specification and pattern formation during development. The anteroposterior and dorsoventral axes of the Drosophila melanogaster embryo are determined by the activities of localized maternal gene products. At the posterior pole of the oocyte, Oskar directs the assembly of the pole plasm, and is thus responsible for formation of abdomen and germline in the embryo. Tight restriction of oskar activity is achieved by mRNA localization, localization-dependent translation, anchoring of the RNA and protein, and stabilization of Oskar at the posterior pole. Here we report that the type 1 regulatory subunit of cAMP-dependent protein kinase (Pka-R1) is crucial for the restriction of Oskar protein to the oocyte posterior. Mutations in PKA-R1 cause premature and ectopic accumulation of Oskar protein throughout the oocyte. This phenotype is due to misregulation of PKA catalytic subunit activity and is suppressed by reducing catalytic subunit gene dosage. These data demonstrate that PKA mediates the spatial restriction of Oskar for anteroposterior patterning of the Drosophila embryo and that control of PKA activity by PKA-R1 is crucial in this process.

03-P128 Quantitative analysis of morphogen activity gradient in Drosophila wing patterning

ted embryo. Using the example of a Forkhead binding site, we will show that this approach allows detection of very limited changes in enhancer activity in a whole embryo and, in particular, makes possible the identification of repressor binding sites that are usually difficult to detect. We will also discuss the possible implications of the presence of this Forkhead repressor binding site on hindbrain patterning.