A new chromosome 14-based human artificial chromosome (HAC) vector system for efficient transgene expression in human primary cells.

The use of non-integrating human artificial chromosomes (HACs) in gene therapy possibly allows for safe and reliable genetic modification of human cells without insertional mutagenesis and/or unexpected oncogene activations. Although we previously demonstrated that the HAC provides long-term therapeutic erythropoietin (EPO) production in normal human primary fibroblasts (hPFs), the expression level of EPO was too low to provide medical benefits for human therapy. Thus, the next challenge for the application of this system in therapeutic purposes is to improve the transgene expression on HACs. Here, we newly constructed chromosome 14-based HACs and examined the effects of the telomere and promoter regions on the expression level of the tansgene in hPFs. We showed that the use of natural telomere/sub-telomere and enhancers within the 5' untranslated region of the human ubiquitin C gene greatly increased (over 1000-fold) the EPO production in hPFs. Furthermore, we demonstrated the reprogramming of mouse embryonic fibroblasts by HAC-mediated introduction of four transcription factors, and established induced pluripotent stem cells with no trace of the HACs carrying multiple expression cassettes with large genome fragments. These results indicate that this HAC system could allow us to manipulate multiple transgenes efficiently in human primary cells, providing a promising tool not only for gene therapy but also for investigating genome functions in drug discoveries.

Subcellular localization of Axl1, the cell type-specific regulator of polarity.

Bud-site selection in yeast offers an attractive system for studying cell polarity and asymmetric division. Haploids divide in an axial pattern, whereas diploids divide in a bipolar pattern. AXL1 is expressed in haploids but not diploids, and ectopic expression of AXL1 in diploids converts their bipolar budding pattern to an axial pattern. How Axl1 acts as a switch between the bipolar and axial patterns is not understood. Here we report that Axl1 localizes to the mother-bud neck and division site remnants of haploids. Axl1 is absent from diploids. Axl1 colocalizes with Bud3, Bud4, and Bud10, components of the axial landmark structure. This localization suggests that Axl1 couples the axial landmark with downstream polarity establishment factors. Consistent with such a role, Axl1 associated biochemically with Bud4 and Bud5. Genetic evidence suggests that Axl1 works with Bud3 and Bud4 to promote the activity of the Bud10 membrane protein. Given Axl1's suggested role in morphogenesis and cell fusion during mating, we also examined its localization during this process. Axl1 redistributes independently of the axial landmark to a tight cell surface dot at the tip of each mating projection. These dots are rapidly lost as prezygotes form.

The binding of chondroitin sulfate to pleiotrophin/heparin-binding growth-associated molecule is regulated by chain length and oversulfated structures.

Pleiotrophin is an 18-kDa heparin-binding growth factor, which uses chondroitin sulfate (CS) proteoglycan, PTPzeta as a receptor. It has been suggested that the D-type structure (GlcA(2S)beta1-3GalNAc(6S)) in CS contributes to the high affinity binding between PTPzeta and pleiotrophin. Here, we analyzed the interaction of shark cartilage CS-D with pleiotrophin using a surface plasmon resonance biosensor to reveal the importance of D-type structure. CS-D was partially digested with chondroitinase ABC, and fractionated using a Superdex 75pg column. The > or =18-mer CS fractions showed significant binding to pleiotrophin, and the longer fractions had stronger affinity for pleiotrophin than the shorter ones. The approximately 46-mer CS fraction bound to densely immobilized pleiotrophin with high affinity (K(D) = approximately 30 nM), and the binding reactions fitted the bivalent analyte model. However, when the density of the immobilized pleiotrophin was lowered, the strength of affinity remarkably decreased (K(D) = approximately 2.5 microM), and the reactions no longer fitted the model and were considered to be monovalent binding. The 20 approximately 24-mer fractions showed low affinity binding to densely immobilized pleiotrophin (K(D) = 3 approximately 20 microM), which seemed to be monovalent. When approximately 22-mer CS oligosaccharides were fractionated by strong anion exchange HPLC, each fraction differed in affinity for pleiotrophin (K(D) = 0.36 approximately >10 microM), and the affinity correlated with the amounts of D- and E- (GlcAbeta1-3GalNAc(4S,6S)) type oversulfated structures. These results suggest that the binding of pleiotrophin to CS is regulated by multivalency with CS approximately 20 mer as a unit and by the amounts of oversulfated structures.

Gamete fusion and cytokinesis preceding zygote establishment in the sexual process of Dictyostelium discoideum.

Cells of Dictyostelium discoideum become sexually mature under submerged and dark conditions, and fuse with opposite mating-type cells to form zygote giant cells, which gather surrounding cells and finally develop into dormant structures called macrocysts. In the present study, we found that the multinuclear fused cells formed during this process frequently underwent cytokinesis driven by random local movements. The split cells were capable of re-fusion, and repeated cytokinesis. These radical behaviors continued until the extensive cell aggregation started around the giant cells. Thus, gamete fusion and initiation of zygote development do not coincide in the mating of D. discoideum. Analyses by confocal microscopy and flow cytometry indicated that the cessation of the random movement followed pronuclear fusion, and that microtubule organizing centers (MTOC), abundant in the fused cells at the beginning, gradually decreased and only one of them remained within the developed macrocyst. Some of the genes known to control cell movement, such as rasGEFB and rasS, increased shortly before the cessation of repeated fusion-cytokinesis and initiation of phagocytosis. These results suggest that the sequential molecular events are necessary in D. discoideum after gamete fusion to establish a new individuality of zygotes.

Developmental and regional expression of heparan sulfate sulfotransferase genes in the mouse brain.

Heparan sulfate (HS) binds with various proteins including growth factors, morphogens, and extracellular matrix molecules to regulate their biological functions. These regulatory interactions are considered to be dependent on the structure of HS, which is determined by HS sulfotransferases. To gain insights into the functions of HS sulfotransferases in the development of the nervous system, we examined the expression of these enzymes (3-O-sulfotransferase-1 [3-OST-1], -2, -4; 6-OST-1, -2, -3; and N-deacetylase /N-sulfotransferase-1 [NDST-1], -2, -3) by in situ hybridization and real-time reverse transcription-polymerase chain reaction (RT-PCR). The expression of these genes was spatiotemporally regulated. In the E16 cerebrum, the expression of these genes showed two patterns: (1) selective expression at cortical plate (CP) and ventricular zone (VZ) and (2) wider expression by the cells in the marginal zone (MZ), CP, subplate (SP), and VZ. At P1, most genes showed similar expression patterns, but after P7, these genes were expressed differentially in a layer-specific manner. In the P1 cerebellum, the external granule cell layer (EGL) expressed most genes, the expressions of which were down-regulated at P7. In contrast, Purkinje cells began to express many of these genes after P7. These complex expression patterns suggest that the structure of HS is altered spatiotemporally for regulating various biological activities in the developing brain including the proliferation of neuronal progenitors, extension of axons, and formation of dendrites. We discuss possible functional roles of these sulfotransferases in the signaling of several HS-binding proteins such as fibroblast growth factors, slit, netrin, and sonic hedgehog.

Developmental change and function of chondroitin sulfate deposited around cerebellar Purkinje cells.

Chondroitin sulfate is a long sulfated polysaccharide with enormous structural heterogeneity that binds with various proteins, such as growth factors, in a structure-dependent manner. In this study, we analyzed the expression of chondroitin sulfate in the postnatally developing cerebellar cortex by using three monoclonal antibodies against chondroitin sulfate, MO-225, 2H6, and CS-56, which recognize different structural domains in this polysaccharide. During the first postnatal week, the patterns of immunohistochemical staining made by these antibodies were quite similar, and the molecular layer, the granule cell layer, and Bergmann glial fibers in the external granular layer were densely stained. After postnatal day 12 (P12), the expression of 2H6 epitopes was down-regulated in the molecular layer, and the expression of CS-56 epitopes in this layer was also reduced after P16. On the other hand, the strong expression of MO-225 epitopes, GlcA(2S)beta1-3GalNAc(6S) (D unit)-containing structures, remained until adulthood. These chondroitin sulfate epitopes were observed around Purkinje cells, including cell soma and dendrites. Detailed immunohistochemical analysis suggested that chondroitin sulfate was deposited between Purkinje cell surfaces and the processes of Bergmann glia. Furthermore, the amount of pleiotrophin, a heparin-binding growth factor, in the cultured cerebellar slices was remarkably diminished after treatment with chondroitinase ABC or D unit-rich chondroitin sulfate. With the previous findings that pleiotrophin binds to D unit-rich chondroitin sulfate, we suggest that the D-type structure is important for the signaling of pleiotrophin, which plays roles in Purkinje cell-Bergmann glia interaction, and that the structural changes of chondroitin sulfate regulate this signaling pathway.