Echinoids (sea urchins) are divided into two major groups -cidaroids (a 'primitive' group) and euechinoids (a 'derived' group). The cidaroids are a promising model species for understanding the ancestral developmental mechanisms in echinoids, but little is known about the molecular mechanisms of cidaroid development. In euechinoids, skeletogenic mesenchyme cell specification is regulated by the double-negative gate (DNG), in which hesC represses the transcription of the downstream mesenchyme specification genes (alx1, tbr and ets1), thereby defining the prospective mesenchyme region. To estimate the ancestral mechanism of larval mesenchyme cell specification in echinoids, the expression patterns and roles of mesenchyme specification genes in the cidaroid Prionocidaris baculosa were examined. The present study reveals that the expression pattern and function of hesC in P. baculosa were inconsistent with the DNG model, suggesting that the euechinoidtype DNG is not utilized during cidaroid mesenchyme specification. In contrast with hesC, the expression patterns and functions of alx1, tbr and ets1 were similar between P. baculosa and euechinoids. Based on these results, we propose that the roles of alx1, tbr and ets1 in mesenchyme specification were established in the common ancestor of echinoids, and that the DNG system was acquired in the euechinoid lineage after divergence from the cidaroid ancestor. The evolutionary timing of the establishment of the DNG suggests that the DNG was originally related to micromere and/or primary mesenchyme cell formation but not to skeletogenic cell differentiation.

The effect of Co(II) ion on the reaction of hydrogen peroxide with DNA was investigated by a DNA sequencing technique using 32P-5'-end-labeled DNA fragments obtained from human c-Ha-ras-1 protooncogene. Co(II) induced strong DNA cleavage in the presence of hydrogen peroxide even without alkali treatment. Guanine residues were the most alkali-labile site, and the extent of cleavages at the positions of thymine and cytosine was dependent on the sequence. Adenine residues were relatively resistive. Diethylenetriaminepentaacetic acid, present in excess over Co(II), inhibited DNA cleavage. Singlet oxygen scavengers (dimethylfuran, sodium azide, 1,4-diazabicyclo[2.2.2]octane, dGMP), sulfur compounds (methional, methionine), and superoxide dismutase inhibited DNA cleavage completely. Hydroxyl radical scavengers were not so effective as singlet oxygen scavengers. ESR studies using 2,2,6,6-tetramethyl-4-piperidone as a singlet oxygen trap suggest that Co(II) reacts with hydrogen peroxide to produce singlet oxygen or its equivalent. ESR studies using 5,5-dimethylpyrroline N-oxide (DMPO) showed that the hydroxyl radical adduct of DMPO was also formed. The results suggest that Co(II) ion binds to DNA and subsequently reacts with hydrogen peroxide to produce singlet oxygen and hydroxyl radicals and that singlet oxygen plays a more important role in the DNA damage than hydroxyl free radicals.

The animal-vegetal axis of sea urchin embryos is morphologically apparent at the 16-cell stage, when the mesomeres, macromeres, and micromeres align along it. At this stage, the micromere is the only autonomously specified blastomere that functions as a signaling center. We used a subtraction PCR survey to identify the homeobox gene micro1 as a micromere-specific gene. The micro1 gene is a representative of a novel family of paired-like class homeobox genes, along with PlHbox12 from Paracentrotus lividus and pmar1 from Strongylocentrotus purpuratus. In the present study, we showed that micro1 is a multicopy gene with six or more polymorphic loci, at least three of which are clustered in a 30-kb region of the genome. The micro1 gene is transiently expressed during early cleavage stages in the micromere. Recently, nuclear beta-catenin was shown to be essential for the specification of vegetal cell fates, including micromeres, and the temporal and spatial coincidence of micro1 expression with the nuclear entry of beta-catenin is highly suggestive. We demonstrated that micro1 is a direct target of beta-catenin. In addition, we showed that micro1 is necessary and sufficient for micromere specification. These observations on the structure, regulation, and function of micro1 lead to the conclusion that micro1 and pmar1 (and potentially PlHbox12) are orthologous.

These studies suggest that knowledge of the initial depth distribution of fallout radionuclides is important for future decontamination work and countermeasures to reduce the transfer of radionuclides to agricultural products. In order to determine how the initial depth distribution of the radioactive substances varies depending on field type, such as wheat fields, rice paddies, orchards, and forestland, we need to take measurements at locations with different land-use patterns but with nearly equal exposure to radioactive fallout. The Fukushima Agricultural Technology Centre has wheat fields, rice paddies, orchards, and forestland all enclosed within a 500 × 500 m test site. At this test site, we sampled and determined the depth profiles of radiocesium and radioiodine for each type of land use. On the basis of these depth profiles, we derived an estimate of the deposition density to clarify the influence that land use has on the distribution pattern of radionuclides in soils. Several other studies have been also conducted in this issue for the distribution of the radionuclides on land and mechanism of retention of radiocesium at soil surface (

Understanding tropical nutrient dynamics is essential for quantifying marine productivity. In tropical and subtropical oceans, however, the spatial and continuous observation of nutrients has been scarce because of low nutrient concentration. The nitrogen isotopes of organic nitrogen in coral skeletons (δ15N_[coral]) could be used to record nitrogenous nutrient origins at oceanic surfaces. Here, we show the intra- and inter-reef variations of δ15N_[coral] in the western Pacific. The zonal distribution of δ15N_[coral] was found inside a coral reef corresponding with δ15N of seawater nitrate (δ15N_[nitrate]). The extended analysis of δ15N_[coral] among various coral reefs also shows a latitudinal gradient from tropical to temperate in the western Pacific. The δ15N_[coral] records high-resolution dynamics of nitrogenous nutrients through the geologic time scale