High-electron-mobility (370 cm2/Vs) polycrystalline Ge on an insulator formed by As-doped solid-phase crystallization.

High-electron-mobility polycrystalline Ge (poly-Ge) thin films are difficult to form because of their poor crystallinity, defect-induced acceptors and low solid solubility of n-type dopants. Here, we found that As doping into amorphous Ge significantly influenced the subsequent solid-phase crystallization. Although excessive As doping degraded the crystallinity of the poly-Ge, the appropriate amount of As (~1020 cm-3) promoted lateral growth and increased the Ge grain size to approximately 20 µm at a growth temperature of 375 °C. Moreover, neutral As atoms in poly-Ge reduced the trap-state density and energy barrier height of the grain boundaries. These properties reduced grain boundary scattering and allowed for an electron mobility of 370 cm2/Vs at an electron concentration of 5 × 1018 cm-3 after post annealing at 500 °C. The electron mobility further exceeds that of any other n-type poly-Ge layers and even that of single-crystal Si wafers with n ≥ 1018 cm-3. The low-temperature synthesis of high-mobility Ge on insulators will provide a pathway for the monolithic integration of high-performance Ge-CMOS onto Si-LSIs and flat-panel displays.

cDNA cloning of calcineurin heterosubunits from the pheromone gland of the silkmoth, Bombyx mori.

Pheromone biosynthesis activating neuropeptide (PBAN) stimulates the step of fatty acyl reduction in the pheromone biosynthetic pathway of the silkmoth, Bombyx mori. It has been suggested that the intracellular signal transduction of PBAN in B. mori involves Ca(2+), calmodulin, and calcineurin (also known as protein phosphatase 2B). We have cloned two cDNAs encoding calcineurin heterosubunits from a pheromone gland cDNA library of B. mori. The 2,996-bp clone predicts a 495-amino acid protein homologous to the catalytic subunit calcineurin A (CnA) with a molecular mass of 55,968. The deduced amino acid sequence well conserves the calcineurin B (CnB)-binding domain and two subdomains, a calmodulin-binding and an autoinhibitory domain, showing 77-85% and 82% identities to the isoforms of Drosophila melanogaster CnA and human CnA, respectively. On the other hand, the 820-bp clone predicts a 170-amino acid protein homologous to the regulatory subunit CnB with a molecular mass of 19,357. The deduced amino acid sequence well conserves four EF-hand type calcium-binding structures, showing 95% and about 85% identities to D. melanogaster CnB and mammalian CnBs, respectively. A yeast two-hybrid system has demonstrated the molecular interaction between B. mori CnA and CnB. Northern blot analyses revealed that both CnA and CnB genes were expressed in various larval and adult tissues of B. mori. Both transcripts detected in the pheromone gland three days before adult eclosion increased by the day before eclosion and the mRNA levels were found to be high even two days after adult eclosion. Immunohistochemical analysis has revealed that B. mori calcineurin is localized in the cytoplasm of the pheromone-producing cells.

Gene transfer into insect brain and cell-specific expression of bombyxin gene.

A transgene reporter consisting of the bombyxin gene promoter and the green fluorescent protein coding region was introduced into intact brains of the silkworm Bombyx mori by in vitro electroporation. After in vitro culture of the brains, the fluorescence derived from the introduced reporter gene was observed in all cases in eight neurosecretory cells that had previously been identified as bombyxin-producing cells (BPCs). Although the fluorescence was not always observed in all cells, it was specific to BPCs, indicating that the reporter was under the control of the bombyxin gene promoter in a BPC-specific manner. Electroporatical introduction of a reporter gene was therefore found to be a suitable method for analyzing cell-specific expression in intact tissues and to be substitute for germ-line transmission of reporters in the transgenic system. Application of this technique enables us to analyze the cell-specific expression of transgene reporters within a few days and treat more than several dozens of the reporters within 1 month, which is difficult to do with the transgenic system.

A novel member of the bombyxin gene family: structure and expression of bombyxin G1 gene, an insulin-related peptide gene of the silkmoth Bombyx mori.

Bombyxin G1 gene, a novel insulin-related peptide gene of the silkmoth Bombyx mori, has been identified. The G1 gene encodes a precursor peptide which shows 41-56% and 28% sequence identities with preprobombyxins previously characterized and human preproinsulin, respectively. The G1 gene forms a pair with bombyxin C2 gene with opposite transcriptional orientation in a bombyxin gene cluster. The bombyxin G1 mRNA in Bombyx brain was shown to locate in four pairs of medial neurosecretory cells.