Dependence of timing of mitotic events on the rate of protein synthesis and DNA replication in sea urchin early cleavages

Cost of protein synthesis and energy allocation during development of antarctic sea urchin embryos and larvae

Cold environments represent a substantial volume of the biosphere. To study developmental physiology in subzero seawater temperatures typically found in the Southern Ocean, rates and costs of protein synthesis were measured in embryos and larvae of Sterechinus neumayeri, the Antarctic sea urchin. Our analysis of the "cost of living" in extreme cold for this species shows (1) that cost of protein synthesis is strikingly low during development, at 0.41 +/- 0.05 J (mg protein synthesized)(-1) (n = 16); (2) that synthesis cost is fixed and independent of synthesis rate; and (3) that a low synthesis cost permits high rates of protein turnover at -1 degrees C, at rates comparable to those of temperate species of sea urchin embryos developing at 15 degrees C. With a low synthesis cost, even at the highest synthesis rates measured (gastrulae), the proportion of total metabolism accounted for by protein synthesis in the Antarctic sea urchin was 54%-a value similar to that of temperate sea urchin embryos. In the Antarctic sea urchin, up to 87% of metabolic rate can be accounted for by the combined energy costs of protein synthesis and the sodium pump. We conclude that, in Antarctic sea urchin embryos, high rates of protein synthesis can be supported in extreme-cold environments while still maintaining low rates of respiration.

Cytotoxicity in the marine dinoflagellate Prorocentrum mexicanum from Brazil

The microscopic algae in the oceans are crucial food for filter feeding bivalve shellfish (oysters, mussels, scallops, clams, etc.) as well as for the larvae of commercially important crustaceans. Some species of microalgae have the capacity to produce potent toxins, such as saxitoxins and ciguatoxins, which may intoxicate humans. Among the marine phytoplankton, the dinoflagellates are the main toxin producers. Studies on the marine phytoplankton from the São Sebastião Channel, southeastern coast of Brazil, showed a great diversity of dinoflagellates. Some species were collected and cultured at the Marine Biology Center of the São Paulo University (USP). The polar (PEs) (aqueous) and apolar (AEs) (methylene chloride) extracts of the cultivated dinoflagellate species were tested on different stages of the sea urchin development, on mouse erythrocytes and on microfilaments organization in a neuroblastoma cell line. Prorocentrum mexicanum PE and AE induced cells anomalies and cell division inhibition of sea urchin eggs at EC50 of 78.75 microg/mL (95% CI from 32.56 to 190.50) and 22.50 microg/mL (95% CI from 2.96 to 170.80) respectively (n=3). Both AE and PE of P. mexicanum induced hemolysis with EC50 of 65.07 microg/mL (95% CI from 27.40 to 154.60) and 84.29 microg/mL (95% CI from 53.26 to 133.40 microg/mL), respectively. P. mexicanum PE was tested in immunofluorescence for actin filaments organization in neuroblastoma cultured cell.

Fixed metabolic costs for highly variable rates of protein synthesis in sea urchin embryos and larvae

Defining the physiological mechanisms that set metabolic rates and the`cost of living' is important for understanding the energy costs of development. Embryos and larvae of the sea urchin Lytechinus pictus(Verrill) were used to test hypotheses regarding differential costs of protein synthesis in animals differing in size, rates of protein synthesis, and physiological feeding states. For embryos, the rate of protein synthesis was 0.22±0.014 ng protein embryo-1 h-1 (mean ±s.e.m.) and decreased in unfed larvae to an average rate of 0.05±0.001 ng protein larva-1 h-1. Fed larvae had rates of synthesis that were up to 194 times faster than unfed larvae (9.7±0.81 ng protein larva-1 h-1). There was no significant difference, however, in the cost of protein synthesis between these larvae with very different physiological states. Furthermore, the cost of synthesis in the larval stages was also similar to costs measured for blastula and gastrula embryos of 8.4±0.99 J mg-1 protein synthesized. The cost of protein synthesis was obtained using both direct (`inhibitor') and indirect (`correlative') measurements; both methods gave essentially identical results. Protein synthesis accounted for up to 54±8% of metabolic rate in embryos. Percent of metabolism accounted for by protein synthesis in larvae was dependent on their physiological feeding state, with protein synthesis accounting for 16±4% in unfed larvae and 75±11% in fed larvae. This regulation of metabolic rate was due to differential rates of synthesis for a fixed energy cost per unit mass of protein synthesized. The cost of synthesizing a unit of protein did not change with increasing rates of protein synthesis. We conclude that the cost of protein synthesis is independent of the rate of synthesis, developmental stage, size and physiological feeding state during sea urchin development.

The cytotoxic and embryotoxic effects of kaurenoic acid, a diterpene isolated from Copaifera langsdorffii oleo-resin

In this work, we studied the effects of kaurenoic acid, a diterpene isolated from the oleo-resin of Copaifera langsdorffii in developing sea urchin (Lytechinus variegatus) embryos, on tumor cell growth in microculture tetrazolium (MTT) test and on mouse and human erythrocytes in hemolysis assay. Continuous exposure of embryos to kaurenoic acid starting immediately after fertilization inhibited the first cleavage (IC(50): 84.2 microM) and progressively induced embryo destruction (IC(50): 44.7 microM and < 10 microM for blastulae and larvae stages, respectively). In MTT assay, kaurenoic acid at a concentration of 78 microM produced growth inhibition of CEM leukemic cells by 95%, MCF-7 breast and HCT-8 colon cancer cells by 45% each. Further, kaurenoic acid induced a dose-dependent hemolysis of mouse and human erythrocytes with an EC(50) of 74.0 and 56.4 microM, respectively. The destruction of sea urchin embryos, the inhibition of tumor cell growth and the hemolysis of mouse and human erythrocytes indicate the potential cytotoxicity of kaurenoic acid.

Pesticide Roundup provokes cell division dysfunction at the level of CDK1/cyclin B activation

To assess human health risk from environmental chemicals, we have studied the effect on cell cycle regulation of the widely used glyphosate-containing pesticide Roundup. As a model system we have used sea urchin embryonic first divisions following fertilization, which are appropriate for the study of universal cell cycle regulation without interference with transcription. We show that 0.8% Roundup (containing 8 mM glyphosate) induces a delay in the kinetic of the first cell cleavage of sea urchin embryos. The delay is dependent on the concentration of Roundup. The delay in the cell cycle could be induced using increasing glyphosate concentrations (1-10 mM) in the presence of a subthreshold concentration of Roundup 0.2%, while glyphosate alone was ineffective, thus indicating synergy between glyphosate and Roundup formulation products. The effect of Roundup was not lethal and involved a delay in entry into M-phase of the cell cycle, as judged cytologically. Since CDK1/cyclin B regulates universally the M-phase of the cell cycle, we analyzed CDK1/cyclin B activation during the first division of early development. Roundup delayed the activation of CDK1/cyclin B in vivo. Roundup inhibited also the global protein synthetic rate without preventing the accumulation of cyclin B. In summary, Roundup affects cell cycle regulation by delaying activation of the CDK1/cyclin B complex, by synergic effect of glyphosate and formulation products. Considering the universality among species of the CDK1/cyclin B regulator, our results question the safety of glyphosate and Roundup on human health.

High-mobility group proteins 14 and 17 maintain the timing of early embryonic development in the mouse

The high-mobility group (HMG) proteins 14 and 17 are abundant chromosomal proteins that bind to nucleosomes and enhance transcription. We report that both mRNA species and both proteins are present throughout oogenesis and preimplantation development of the mouse. When antisense oligonucleotides targeting each mRNA species are injected into one-cell embryos, the proteins become depleted at the two- and four-cell stages and reaccumulate at the eight-cell stage. One-cell embryos injected with antisense oligonucleotides targeting both HMG-14 and HMG-17 cleave to the two-cell stage. Subsequent cleavages, however, are delayed compared with control-injected embryos. Nevertheless, these embryos ultimately reach the blastocyst stage. Similarly, injection into the nuclei of two-cell embryos of a peptide corresponding to the common nucleosome-binding domain of HMG-14 and HMG-17 delays progression to the four-cell stage. Furthermore, both RNA and protein synthesis is transiently reduced in antisense-injected embryos compared with injected controls. These results identify HMG-14 and HMG-17 as constitutive components of mouse oocyte and embryonic chromatin and establish a link between the structure of embryonic chromatin and the normal progression of embryonic development.