Defense mechanisms of sargassacean species against the epiphytic red alga Neosiphonia harveyi.

Flora diversity and abundance of epiphytes are specific to their basiphyte species and may relate to variations in the defensive abilities of basiphytes. Thus, investigating the interactions between epiphytes and basiphytes is useful for a better understanding of the biological impact of epiphytism and the survival strategies of basiphytes. We examined the epiphyte density on five sargassacean species at six locations between two study sites, which showed that the epiphytic red alga Neosiphonia harveyi was remarkably less abundant on Sargassum siliquastrum at all locations. To assess its defense mechanism against N. harveyi, we performed bioassays of phlorotannins, which are considered effective in deterring fouling, by culturing sargassacean blades with N. harveyi carpospores and observed the process by which sargassacean blades remove epiphytes. When the carpospores were incubated with various concentrations of dissolved phlorotannins, settlement and germination were inhibited only at the highest concentrations (>0.1 g · L(-1) ), and this effect did not significantly differ among the five sargassacean species. When the carpospores were combined with blades from the five species, many of the spores attached and germinated on every blade. Because N. harveyi penetrated rhizoids into basiphyte tissues, cuticle peeling observed in all five sargassacean species could not remove this epiphyte after germination. However, in S. siliquastrum, the blade tissues around the germlings became swollen and disintegrative, and were removed together with the germlings. The spores normally grew on the dead blades, suggesting that the tissue degradation of S. siliquastrum is triggered by the infection of N. harveyi.

MRG-1, a mortality factor-related chromodomain protein, is required maternally for primordial germ cells to initiate mitotic proliferation in C. elegans.

We identified MRG-1, a Caenorhabditis elegans chromodomain-containing protein that is similar to the human mortality factor-related gene 15 product (MRG15). RNA-mediated interference (RNAi) of mrg-1 resulted in complete absence of the germline in both hermaphrodite and male adults. Examination of the expression of PGL-1, a component of P granules, revealed that two primordial germ cells (PGCs) are produced during embryogenesis in mrg-1(RNAi) animals, but these PGCs cannot undergo mitotic proliferation, and they ultimately degenerate during post-embryonic development. Zygotic RNAi experiments using RNAi-deficient hermaphrodites and wild-type males demonstrated that MRG-1 functions maternally. Moreover, immunoblot analysis using mutant animals with germline deficiencies indicated that MRG-1 is synthesized predominantly in oocytes. These results suggest that MRG-1 is required maternally to form normal PGCs with the potential to start mitotic proliferation during post-embryonic development.

A systematic genome-wide screen for mutations affecting organogenesis in Medaka, Oryzias latipes.

A large-scale mutagenesis screen was performed in Medaka to identify genes acting in diverse developmental processes. Mutations were identified in homozygous F3 progeny derived from ENU-treated founder males. In addition to the morphological inspection of live embryos, other approaches were used to detect abnormalities in organogenesis and in specific cellular processes, including germ cell migration, nerve tract formation, sensory organ differentiation and DNA repair. Among 2031 embryonic lethal mutations identified, 312 causing defects in organogenesis were selected for further analyses. From these, 126 mutations were characterized genetically and assigned to 105 genes. The similarity of the development of Medaka and zebrafish facilitated the comparison of mutant phenotypes, which indicated that many mutations in Medaka cause unique phenotypes so far unrecorded in zebrafish. Even when mutations of the two fish species cause a similar phenotype such as one-eyed-pinhead or parachute, more genes were found in Medaka than in zebrafish that produced the same phenotype when mutated. These observations suggest that many Medaka mutants represent new genes and, therefore, are important complements to the collection of zebrafish mutants that have proven so valuable for exploring genomic function in development.

A Novel Mesoderm-Specific cDNA Isolated from a Mouse Embryonal Carcinoma Cell Line: (embryonal carcinoma cell/cDNA/in situ hybridization/mesoderm/mouse embryo).

A novel mesoderm-specific cDNA clone has been isolated by differential screening of cDNA library from an embryonal carcinoma (EC) cell line MC12. The cDNA clone 121a is about 2.5 kb in length and apparently encodes a putative polypeptide of 335 amino acids which may be secreted or membrane anchored glycoprotein since it has a possible signal sequence and a potential N-linked glycosylation site. In situ hybridization using mouse embryos revealed that 121a expression was confined to mesoderm and its derivatives such as allantois, the mesodermal layer of amnion, chorion and yolk sac, somites, heart, etc. These findings suggest that 121 a may be essential for mesodermal differentiation or function, although nothing definite is known. Conservation of 121a homolog in mammals and even in Drosophila seems to support this presumption. Fluorescence in situ hybridization successfully localized 121a to B1 band of mouse chromosome 6.

c-Jun and Sp1 family are critical for retinoic acid induction of the lamin A/C retinoic acid-responsive element.

The expression of A-type lamins, subdivided into lamin A and C, is developmentally regulated. Retinoic acid (RA)-induced differentiation of P19 embryonic carcinoma cells, in which A-type lamins are absent, increases the expression of lamin A/C. We previously showed, using P19 cells as a model system, that the lamin A/C promoter has a retinoic acid-responsive element (L-RARE), and that Sp1 and Sp3 bind the CACCC box of the L-RARE. In this study, we report that Sp1, Sp3, and c-Jun increase transactivation of the L-RARE during RA treatment. Sp1 and Sp3 regulate the lamin A/C promoter in Sp1-deficient SL2 cells and contribute to RA-dependent activation in GAL4-based transcriptional assays. Overexpression of c-Jun causes transactivation of a chimeric promoter consisting of four tandem L-RARE repeats fused with the luciferase gene in P19 cells. c-Jun also transactivates a reporter construct with five tandem GAL4-binding sites, only when co-expressed with either GAL4-Sp1 or Sp3 fusion proteins. Furthermore, we detect a physiological interaction between c-Jun with Sp1/Sp3 in RA-treated cells. Our data suggest that Sp1, Sp3, and c-Jun play an important role in gene expression through the L-RARE during RA treatment.

Non-sequence-specific DNA binding by the FILAMENTOUS FLOWER protein from Arabidopsis thaliana is reduced by EDTA.

The FILAMENTOUS FLOWER protein has a zinc finger domain, hydrophobic region, proline-rich region, and a HMG box-like domain. We have reported that zinc release at the zinc finger is probably facilitated by the non-canonical cysteine residue at position 56, and that EDTA causes the structural change and enhances the self-assembly of the protein (Kanaya, E., Watanabe, K., Nakajima, N., Okada, K., and Shimura, Y. (2001) J. Biol. Chem. 276, 7383-7390). To investigate this aspect further we examined the DNA binding function of the FILAMENTOUS FLOWER protein. Gel retardation experiments showed that the FILAMENTOUS FLOWER protein binds to DNA without sequence specificity. Deletion analyses suggested that the zinc finger domain and the hydrophobic region are not required but the proline-rich region and the HMG box-like domain are indispensable for the DNA binding by the FILAMENTOUS FLOWER protein. The DNA binding by the protein consisting of the zinc finger domain and the rest of the regions was reduced with the addition of EDTA. This result probably suggests that the zinc release, the structural change probably occurring in the zinc finger domain, the intermolecular interaction, and the self-assembly of the protein are related to the dissociation of the FILAMENTOUS FLOWER protein from DNA.

Pax6 autoregulation mediated by direct interaction of Pax6 protein with the head surface ectoderm-specific enhancer of the mouse Pax6 gene.

The Pax6 gene plays crucial roles in eye development and encodes a transcription factor containing both a paired domain and a homeodomain. During embryogenesis, Pax6 is expressed in restricted tissues under the direction of distinct cis-regulatory regions. The head surface ectoderm-specific enhancer of mouse Pax6 directs reporter expression in the derivatives of the ectoderm in the eye, such as lens and cornea, but the molecular mechanism of its control remains largely unknown. We identified a Pax6 protein-responsive element termed LE9 (52 bp in length) within the head surface ectoderm-specific enhancer. LE9, a sequence well conserved across vertebrates, acted as a highly effective enhancer in reporter analyses. Pax6 protein formed in vitro a complex with the distal half of LE9 in a manner dependent on the paired domain. The proximal half of the LE9 sequence contains three plausible sites of HMG domain recognition, and HMG domain-containing transcription factors Sox2 and Sox3 activated LE9 synergistically with Pax6. A scanning mutagenesis experiment indicated that the central site is most important among the three presumptive HMG domain recognition sites. Furthermore, Pax6 and Sox2 proteins formed a complex when they were expressed together. Based on these findings, we propose a model in which Pax6 protein directly and positively regulates its own gene expression, and Sox2 and Sox3 proteins interact with Pax6 protein, resulting in modification of the transcriptional activation by Pax6 protein.