Takeshi Usami

The more and smaller cells mutants of Arabidopsis thaliana identify novel roles for SQUAMOSA PROMOTER BINDING PROTEIN-LIKE genes in the control of heteroblasty.

Regulation of cell number and cell size is essential for controlling the shape and size of leaves. Here, we report a novel class of Arabidopsis thaliana mutants, more and smaller cells 1 (msc1)-msc3, which have increased cell number and decreased cell size in leaves. msc1 has a miR156-resistant mutation in the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 15 (SPL15) gene. msc2 and msc3 are new alleles of paused and squint mutants, respectively. All msc mutants showed accelerated heteroblasty, a phenomenon in which several morphological traits of leaves change along with phase change. Consistent with this finding, in the wild type, leaves at higher nodes (adult leaves) also have increased cell number and reduced cell size compared with those at lower nodes (juvenile leaves). These facts indicate that precocious acquisition of adult leaf characteristics in the msc mutants may cause alterations in the number and size of cells, and that heteroblasty plays an important role in the regulation of cell number and size. In agreement with this suggestion, such heteroblasty-associated changes in cell number and size are severely inhibited by the constitutive overexpression of miR156 and are promoted by the elevated expression of miR156-insensitive forms of SPL genes. By contrast, rdr6, sgs3, zip, arf3 and arf4 mutations, which affect progression of heteroblasty, had little or no effect on number or size of cells. These results suggest that cell number and size are mainly regulated by an SPL-dependent pathway rather than by a tasiR-ARF-dependent pathway.

Powerful red-green-blue laser source pumped with a mode-locked thin disk laser

We present a red-green-blue laser source with average powers of 8 W in the red, 23 W in the green, and 10.1 W in the blue. The entire pump power for the nonlinear conversion stages is provided by a single laser oscillator without any amplifier stages. Our system does not require any synchronized cavities, and all nonlinear crystals except one are critically phase matched at room temperature.

Expression of gonadal soma derived factor (GSDF) is spatially and temporally correlated with early testicular differentiation in medaka

In the teleost fish, medaka (Oryzias latipes), the sex is genetically determined at the time of fertilization. The males are heterogametic with XY chromosome composition, while females are of XX chromosome composition. The male sexual differentiation is initiated in XY embryos of medaka by the sex-determining gene Dmy. In this study, we have cloned the gonadal soma derived factor (Gsdf) from medaka and characterized its expression pattern during the initiation of morphological testicular differentiation. By real-time PCR, an XY-specific up-regulation was detected in the expression levels of Gsdf in the whole embryos of medaka at 6days post fertilization (dpf), coincident with the initiation of testicular differentiation in the XY gonads. Whole mount and section in situ hybridizations reaffirmed that Gsdf was expressed exclusively in primordial gonads of only the genetic males at 6dpf. Conversely, the expression of Gsdf was found to be very weak in the XX gonads during embryogenesis. Importantly, Gsdf and Dmy were found to be co-localized in the same somatic cells in the XY gonads. When the XY embryos were treated with estradiol-17beta, in order to reverse their phenotypic sex, a decline was observed in the expression of Gsdf in these embryos by real-time PCR.

ANGUSTIFOLIA3 signaling coordinates proliferation between clonally distinct cells in leaves.

Coordinated proliferation between clonally distinct cells via inter-cell-layer signaling largely determines the size and shape of plant organs. Nonetheless, the signaling mechanism underlying this coordination in leaves remains elusive because of a lack of understanding of the signaling molecule (or molecules) involved. ANGUSTIFOLIA3 (AN3, also called GRF-INTERACTING FACTOR1) encodes a putative transcriptional coactivator with homology to human synovial sarcoma translocation protein. AN3 transcripts accumulate in mesophyll cells but are not detectable in leaf epidermal cells. However, we found here that in addition to mesophyll cells, epidermal cells of an3 leaves show defective proliferation. This spatial difference between the accumulation pattern of AN3 transcripts and an3 leaf phenotype is explained by AN3 protein movement across cell layers. AN3 moves into epidermal cells after being synthesized within mesophyll cells and helps control epidermal cell proliferation. Interference with AN3 movement results in abnormal leaf size and shape, indicating that AN3 signaling is indispensable for normal leaf development. AN3 movement does not require type II chaperonin activity, which is needed for movement of some mobile proteins. Taking these findings together, we present a novel model emphasizing the role of mesophyll cells as a signaling source coordinating proliferation between clonally independent leaf cells.

Key Proliferative Activity in the Junction between the Leaf Blade and Leaf Petiole of Arabidopsis

Leaves are the most important, fundamental units of organogenesis in plants. Although the basic form of a leaf is clearly divided into the leaf blade and leaf petiole, no study has yet revealed how these are differentiated from a leaf primordium. We analyzed the spatiotemporal pattern of mitotic activity in leaf primordia of Arabidopsis (Arabidopsis thaliana) in detail using molecular markers in combination with clonal analysis. We found that the proliferative zone is established after a short interval following the occurrence of a rod-shaped early leaf primordium; it is separated spatially from the shoot apical meristem and seen at the junction region between the leaf blade and leaf petiole and produces both leaf-blade and leaf-petiole cells. This proliferative region in leaf primordia is marked by activity of the ANGUSTIFOLIA3 (AN3) promoter as a whole and seems to be differentiated into several spatial compartments: activities of the CYCLIN D4;2 promoter and SPATULA enhancer mark parts of it specifically. Detailed analyses of the an3 and blade-on-petiole mutations further support the idea that organogenesis of the leaf blade and leaf petiole is critically dependent on the correct spatial regulation of the proliferative region of leaf primordia. Thus, the proliferative zone of leaf primordia is spatially differentiated and supplies both the leaf-blade and leaf-petiole cells.

Sex Change in the Gobiid Fish Is Mediated through Rapid Switching of Gonadotropin Receptors from Ovarian to Testicular Portion or Vice Versa

Sex-changing fish Trimma okinawae can change its sex back and forth from male to female and then to male serially, depending on the social status in the harem. T. okinawae is well equipped to respond to its social status by possessing both ovarian and testicular tissues even though only one gonad remains active at one time. Here we investigated the involvement of gonadotropins in sex change by determining the changes in gonadotropin receptor (GtHR) gene expression during the onset of sex change from female to male and male to female. The expression of the GtHR was found to be confined to the active gonad of the corresponding sexual phase. During the sex-change from female to male, initially the ovary had high levels of FSHR and LHR, which eventually went up in the testicular tissue if the fish was bigger. Changing of the gonads started with switching of GtHR expression discernible within 8-12 h of the visual cue. Further in vitro culture of the transitional gonads with a supply of exogenous gonadotropin (human chorionic gonadotropin) revealed that the to-be-active gonad acquired the ability to produce the corresponding sex hormone within 1 d of the activation of GtHR. Conversely, the to-be-regressed gonad did not respond to the exogenous gonadotropin. Our findings show that the gonads of successive sex-changing fish possess the intrinsic mechanism to respond to the social cue differentially. Additionally, this location switching of GtHR expression also could substantiate the importance of the hypothalamo-pituitary-gonadotropic axis.

High-power femtosecond fiber-feedback optical parametric oscillator based on periodically poled stoichiometric LiTaO3

We demonstrate a synchronously pumped high-gain optical parametric oscillator with feedback through a fiber, using a passively mode-locked Yb:YAG thin-disk laser as a pump source. We obtain as much as 19-W average signal power at a wavelength of 1.45 microm in 840-fs pulses and 7.8 W of idler power at 3.57 microm. The repetition rate of the pulses is 56 MHz, and the transverse beam quality of the generated signal is M2 < 1.6.

Near-Stoichiometric LiTaO 3 for Bulk Quasi-Phase-Matched Devices

Photorefractive damage at u =532 nm and green-light-induced infrared absorption (GRIIRA) of near-stoichiometric LiTaO 3 (SLT) single crystals were investigated. The SLT crystal even without MgO doping showed high photorefractive damage resistance and suppressed GRIIRA. In addition, a small amount of MgO doped into the SLT crystal almost eliminated the photorefractive damage and GRIIRA. A 3-mm-thick periodically poled SLT (PPSLT) and a 1-mm-thick periodically poled MgO-doped SLT (PPMgSLT) were successfully fabricated and their optical parametric oscillation (OPO) performances were investigated.

Analysis of nonlinear wavelength conversion system for a red-green-blue laser-projection source

We analyze the physical processes in the nonlinear wavelength conversion stages of a recently demonstrated red-green-blue (RGB) laser source, which generated > or = 8 W of average power in each color. The system is based on an infrared femtosecond mode-locked laser and contains a frequency doubler, a parametric generator, a parametric amplifier, and two sum-frequency conversion stages. It does not require any resonant cavities, external laser amplifiers, or nonlinear crystals operated at elevated temperatures; therefore it appears to be more practical than other previously demonstrated RGB laser sources. However, the optimization of the overall system is nontrivial, because pump depletion, birefringence, and temporal walk-off in the first conversion stages lead to spatial and temporal distortion of the interacting beams in the subsequent nonlinear conversion stages. This leads to the interaction of spatially and temporally distorted beams in the later conversion stages. By using a numerical simulation of the nonlinear conversion processes based on a Fourier-space method in one temporal and two transverse spatial dimensions, we can fully take into account these effects. We analyze and discuss the physical effects in the different conversion stages and describe the optimization of the overall system performance.

Nd:YAG-pumped periodically poled LiNbO3 optical parametric generator seeded with the narrowband output of a 532-nm pumped optical parametric generator

We present a simple scheme to generate a continuously tunable pulsed narrow-bandwidth infrared wave. An Nd:YAG-pumped periodically poled lithium niobate optical parametric generator (OPG) is seeded with the output of another OPG pumped by the second harmonic (0.532 microm) of the Nd:YAG laser. A tunable idler wave from the 0.532-microm pumped OPG, operated away from the degenerate point, provides a narrow linewidth seed source for the 1.064-microm pumped broadband OPG. Seeding forces the second OPG to operate in a narrowband operation comparable with that of the seed source. Linewidth of the YAG-pumped OPG is 5-25 nm, in the tuning range of 1.61-1.83 microm (signal), narrowed to 1.48-1.05 nm. Methods of further reduction of linewidth also have been discussed.