Kei Kinoshita

Mesodermal induction in early amphibian embryos by activin A (erythroid differentiation factor)

SummaryRecently the mesoderm-inducing effects of the transforming growth factor β (TGF-β) family of proteins have been widely examined. In an attemt to elucidate the functions of these proteins, porcine inhibin A and activin A (erythroid differentiation factor; EDF) were examined. Treatment of explants with activin A led to differentiation of mesodermal derivatives such as mesenchyme, notochord, blood cells and muscle, but inhibin A had a much lesser effect. The mesodermal differentiation induced by activin A was also comfirmed by analyses using a polyclonal antibody against muscle myosin. By indirect immunofluorescence analysis, the differentiation of muscle blocks was observed in the activin-A-treated explants, whereas no differentiation was observed in inhibin-A-treated and control explants. These findings confirm that this protein of the TGF-β family has mesoderm-inducing ability.

Follistatin inhibits the mesoderm-inducing activity of activin A and the vegetalizing factor from chicken embryo

SummaryThe induction of mesoderm is an important process in early amphibian development. In recent studies, activin has become an effective candidate for a natural mesoderm-inducing factor. In the present study, we show that follistatin, an activin-binding protein purified from porcine ovary, inhibits the mesoderm-inducing activity of recombinant human activin A (rh activin A), which is identical to the erythroid differentiation factor (EDF). The quantity of follistatin required for effective suppression of activin was more than three-fold that of activin (w:w). Follistatin also inhibited the mesoderm-inducing activity of the vegetalizing factor purified from chick embryos, suggesting that the vegetalizing factor is closely related to activin.

Activities of Mesoderm‐Inducing Factors Secreted by Mammalian Cells in Culture1

We have examined the activities of several mesoderm‐inducing factors contained in the culture fluids of phorbol ester (4beta‐phorbol 12‐myristate 13‐acetate;PMA)‐stimulated human cell lines. Mesoderm induction was assayed by examining the differentiation of mesoderm tissues reacted with presumptive ectoderm of the Cynops blastula. The assay system also examined erythroid differentiation activity (EDF activity) in order to test the relationship between mesoderm induction and activin A (EDF). Of 22 human cell lines examined, six strains were positive for both mesoderm‐inducing activity and EDF activity. Four strains showed only mesoderm inducing activity, and one showed only EDF activity. The remaining 11 strains showed neither activity. Therefore, most cell lines secreting mesoderm‐inducing activity also possessed EDF activity. Furthermore, culture fluid of a strain (K‐562) that exhibited both types of activities, was partially fractionated by DEAE‐Toyopearl column chromatography and examined in the same way. The fractions that showed the highest amount of EDF activity were coincident with those displaying mesoderm‐inducing activity. These results suggest that a number of PMA‐stimulated mammalian cell lines have the ability to secrete mesoderm‐inducing factors which are similar to activin A (EDF).

Changes in the adhesive properties of dissociated and reaggregated Xenopus laevis embryo cells

Activin A is a member of the transforming growth factor β superfamily, and the strongest candidate mesoderm‐inducer. The initial adhesive property changes in amphibians are likely to be mediated by mesoderm‐inducers like activin A. The manner in which these changes actually occur, however, remains poorly understood. In the present study, the adhesive property changes mediated by activin A were directly demonstrated. Activin A functioned as a morphogen at low concentrations (less than 0.5 ng/mL), with no effect on the type A adhesive property. But at high concentrations (1 ng/mL), it induced another type of adhesive property, type N, and at very high concentrations (more than 10 ng/mL), it induced yet another type of adhesive property, type Y. Cells that have types A, N, and Y adhesive properties ultimately differentiated into atypical epidermis, notochord, and yolk‐rich cells, respectively. It was also shown that these changes occurred between 5 and 10 h after induction by activin A. The implications of these results for the relationship between the adhesive property acquired during early and later stages of differentiation are also discussed.

Cloning and expression pattern of Xenopus prx-1 (Xprx-1) during embryonic development

Homeobox genes are expressed both temporally and spatially during vertebrate development, and regulate the tissue‐specific expression of other genes. A Xenopus paired‐related homeobox‐1 (Xprx‐1) cDNA was cloned. Xprx‐1 had a paired‐related homeodomain, but did not contain a paired‐box. The sequence of Xprx‐1 had a high level of homology with K‐2(mouse) and Prx‐1(chicken), thus Xprx‐1 is assumed to be the Xenopus homolog of these genes. Xprx‐1 transcripts were maternally restricted, in Xenopus embryos, and a decrease in the late blastula stage was followed by an increase in zygotic transcripts after gastrulation. The transcripts were localized to the animal hemisphere of the late blastula and were concentrated in the branchial arches of the tail‐bud stage embryo. In animal cap experiments, Activin A dose‐dependently induced Xprx‐1 gene expression. These results suggest that Xprx‐1 plays a role in early Xenopus development similar to other species.

Control of Cell Differentiation and Morphogenesis by Activins During Early Amphibian Development

During early vertebrate development, the embryonic body plan is established by cell proliferation, migration, and differentiation. The mechanisms of patterning are complex and likely include multiple so-called induction events. Recent studies of this aspect of developmental biology have been remakably enhanced by the techniques of molecular biology. Most noteworthy is the molecular identification of inducing factors, which are closely associated with determination of the early embryonic axis. Foremost among these are several cell growth factors, including fibroblast growth factors (FGFS) and transforming growth factor-beta (TGF-β).

Photo-thermoelectric detection of cyclotron resonance in asymmetrically carrier-doped graphene two-terminal device

Graphene is known to show a significant photo-thermoelectric effect that can exceed its photovoltaic contribution. Here, by utilizing this effect, we demonstrate a photovoltage measurement of cyclotron resonance in a double-back-gated h-BN/graphene/h-BN two-terminal device. A graphite local bottom gate was fabricated in addition to a p-doped Si global back gate. By tuning the two gate voltages, an in-plane graphene junction having an asymmetric carrier-doping profile was created. With the help of this asymmetric structure, the photo-thermoelectric voltage generated in the vicinity of the metal-electrode/graphene junction was detected. At a low temperature and in the presence of a magnetic field, a photo-induced voltage was measured under the irradiation of an infrared laser (Wavelength= 9.28 to 10.61 micron). We observed a strong enhancement of the photovoltage signal under the cyclotron resonance condition, at which the energy of excitation coincides with a transition between Landau levels. These results highlight the possibility of using the photo-thermoelectric effect in graphene for THz photo-detection.

A 34 kDa protein strongly bound to actively transcribing rDNA of Tetrahymena

Summary Proteins specifically bound to DNA have been implicated to modulate transcription. For the purpose of identifying proteins bound to Tetrahymena rDNA, extrachromosomal nucleoli were isolated and their proteins analyzed. A 34 kDa protein was found to be strongly bound to actively transcribing rDNA, the binding being resistant to 0.5 % Sarkosyl. Fractionation of restriction enzyme digested rDNA chromatin fragments suggested the binding is enriched in a central spacer and/or transcribed gene region of rDNA.