The effect of photosynthetically active radiation and temperature on the photosynthesis of two Vietnamese species of Sargassum,S. mcclurei and S. oligocystum,based on the field and laboratory measurements

SUMMARY The effects of photosynthetically active radiation (PAR) and temperature on the photosynthesis of two Vietnamese brown algae, Sargassum mcclurei and S. oligocystum (Fucales), were determined by field and laboratory measurements. Dissolved oxygen sensors and pulse‐amplitude modulated (PAM) fluorometry were used for the measurements of photosynthetic efficiency. A Diving‐PAM revealed that underwater measurements of the effective quantum yield (Φ _PSII ) of both species declined with increasing incident PAR, with minimum Φ _PSII occurring during noon to early afternoon. Φ _PSII recovered in the evening, indicating photo‐adaptation to excessive PAR. In laboratory experiments, Φ _PSII also decreased under continuous exposure to 1000 μmol photons m^?2 s^?1; and full recovery occurred after 12 h of dark acclimatization. The net photosynthesis – PAR experiments of S. mcclurei and S. oligocystum conducted at 28°C revealed that the net photosynthetic rate quickly increased at PAR below the saturation irradiance of 361 and 301 μmol photons m^?2 s^?1 and nearly saturated to maximum net photosynthetic rates of 385 and 292 μg O₂ g_ww ^{? 1} min^?1 without photoinhibition, respectively. Gross photosynthesis and dark respiration experiments determined over a range of temperatures (12–40°C), revealed that the maximum gross photosynthetic rates of 201 and 147 μg O₂ g_ww ^{? 1} min^?1 occurred at 32.9 and 30.7°C for S. mcclurei and S. oligocystum, respectively. The dark respiration rates increased exponentially over the temperature ranges examined. The estimated maximum value of the maximum quantum yield occurred at 19.3 and 20.0°C and was 0.76 and 0.74, respectively. Similar to the natural habitat of the study site, these two species tolerated the relatively high temperatures and broad range of PAR. The ability of these species to recover from exposure to high PAR is one of the mechanisms that allow them to flourish in the shallow water environment.     

Involvement of the Type IX Secretion System in Capnocytophaga ochracea Gliding Motility and Biofilm Formation

Capnocytophaga ochracea is a Gram-negative, rod-shaped bacterium that demonstrates gliding motility when cultured on solid agar surfaces. C. ochracea possesses the ability to form biofilms; however, factors involved in biofilm formation by this bacterium are unclear. A type IX secretion system (T9SS) in Flavobacterium johnsoniae was shown to be involved in the transport of proteins (e.g., several adhesins) to the cell surface. Genes orthologous to those encoding T9SS proteins in F. johnsoniae have been identified in the genome of C. ochracea; therefore, the T9SS may be involved in biofilm formation by C. ochracea. Here we constructed three ortholog-deficient C. ochracea mutants lacking sprB (which encodes a gliding motility adhesin) or gldK or sprT (which encode T9SS proteins in F. johnsoniae). Gliding motility was lost in each mutant, suggesting that, in C. ochracea, the proteins encoded by sprB, gldK, and sprT are necessary for gliding motility, and SprB is transported to the cell surface by the T9SS. For the ΔgldK, ΔsprT, and ΔsprB strains, the amounts of crystal violet-associated biofilm, relative to wild-type values, were 49%, 34%, and 65%, respectively, at 48 h. Confocal laser scanning and scanning electron microscopy revealed that the biofilms formed by wild-type C. ochracea were denser and bacterial cells were closer together than in those formed by the mutant strains. Together, these results indicate that proteins exported by the T9SS are key elements of the gliding motility and biofilm formation of C. ochracea.     

The sixth transmembrane region of a pheromone G-protein coupled receptor,Map3, is implicated in discrimination of closely related pheromones in Schizosaccharomyces pombe

Most sexually reproducing organisms have the ability to recognize individuals of the same species. In ascomycete fungi including yeasts, mating between cells of opposite mating type depends on the molecular recognition of two peptidyl mating pheromones by their corresponding G-protein coupled receptors (GPCRs). Although such pheromone/receptor systems are likely to function in both mate choice and prezygotic isolation, very few studies have focused on the stringency of pheromone receptors. The fission yeast Schizosaccharomyces pombe has two mating types, Plus (P) and Minus (M). Here, we investigated the stringency of the two GPCRs, Mam2 and Map3, for their respective pheromones, P-factor and M-factor, in fission yeast. First, we switched GPCRs between S. pombe and the closely related species Schizosaccharomyces octosporus, which showed that SoMam2 (Mam2 of S. octosporus) is partially functional in S. pombe, whereas SoMap3 (Map3 of S. octosporus) is not interchangeable. Next, we swapped individual domains of Mam2 and Map3 with the respective domains in SoMam2 and SoMap3, which revealed differences between the receptors both in the intracellular regions that regulate the downstream signaling of pheromones and in the activation by the pheromone. In particular, we demonstrated that two amino acid residues of Map3, F214 and F215, are key residues important for discrimination of closely related M-factors. Thus, the differences in these two GPCRs might reflect the significantly distinct stringency/flexibility of their respective pheromone/receptor systems; nevertheless, species-specific pheromone recognition remains incomplete.     

In vitro and in vivo survival of frozen-thawed bovine oocytes after IVF,nuclear transfer,and parthenogenetic activation

Cryopreservation of bovine oocytes would be beneficial both for nuclear transfer and for preservation efforts. The overall objective of this study was to evaluate the viability as well as the cryodamage to the nucleus vs. cytoplasm of bovine oocytes following freezing-thawing of oocytes at immature (GV) and matured (MII) stages using in vitro fertilization (IVF), parthenogenetic activation, or nuclear transfer assays. Oocytes were collected from slaughterhouse ovaries. Oocytes at the GV, MII, or MII but enucleated (MIIe) stages were cryopreserved in 5% (v/v) ethylene glycol; 6% (v/v) 1,2-propanediol; and 0.1-M sucrose in PBS supplemented with 20% (v/v) fetal bovine serum. Frozen-thawed oocytes were subjected to IVF, parthenogenetic activation, or nuclear transfer assays. Significantly fewer GV oocytes survived (i.e., remained morphologically intact during freezing-thawing) than did MII oocytes (47% vs. 84%). Subsequent development of the surviving frozen-thawed GV and MII oocytes was not different (58% and 60% cleavage development; 7% and 12% blastocyst development at Day 9, respectively, P > 0.05). Parthenogenetic activation of frozen-thawed oocytes resulted in significantly lower rates of blastocyst development for the GV than the MII oocyte groups (1% vs. 14%). Nuclear transfer with cytoplasts derived from frozen-thawed GV, MII, MIIe, and fresh-MII control oocytes resulted in 5%, 16%, 14%, and 17% blastocyst development, respectively. However, results of preliminary embryo transfer trials showed that fewer pregnancies were produced from cloned embryos derived from frozen oocytes or cytoplasts (9%, n = 11 embryos) than from fresh ones (19%, n = 21 embryos). Transfer of embryos derived by IVF from cryopreserved GV and MII oocytes also resulted in term development of calves. Our results showed that both GV and MII oocytes could survive freezing and were capable of developing into offspring following IVF or nuclear transfer. However, blastocyst development of frozen-thawed oocytes remains poorer than that of fresh oocytes, and our nuclear transfer assay suggests that this poorer development was likely caused by cryodamage to the oocyte cytoplasm as well as to the nucleus. Mol. Reprod. Dev. 51:281–286, 1998. © 1998 Wiley-Liss, Inc.     

Regulation of progenitor cell survival by a novel chromatin remodeling factor during neural tube development

During development, progenitor cell survival is essential for proper tissue functions, but the underlying mechanisms are not fully understood. Here we show that ERCC6L2, a member of the Snf2 family of helicase-like proteins, plays an essential role in the survival of developing chick neural cells. ERCC6L2 expression is induced by the Sonic Hedgehog (Shh) signaling molecule by a mechanism similar to that of the known Shh target genes Ptch1 and Gli1. ERCC6L2 blocks programmed cell death induced by Shh inhibition and this inhibition is independent of neural tube patterning. ERCC6L2 knockdown by siRNA resulted in the aberrant appearance of apoptotic cells. Furthermore, ERCC6L2 cooperates with the Shh signal and plays an essential role in the induction of the anti-apoptotic factor Bcl-2. Taken together, ERCC6L2 acts as a key factor in ensuring the survival of neural progenitor cells.     

Prolactin induces MFG-E8 production in macrophages via transcription factor C/EBPβ-dependent pathway

The lactogenic hormone prolactin (PRL) regulates milk protein gene expression in mammary glands. To maintain homeostatic balance in the body, milk fat globule epidermal growth factor 8 (MFG-E8) is vital for phagocytic clearance of apoptotic cells. We investigated the effects of PRL on MFG-E8 expression in macrophages by evaluating its promoter function. Macrophages were stimulated with PRL, and the expression of MFG-E8 was determined using real-time PCR and Western blotting. The role of MFG-E8 on phagocytosis of apoptotic cells in PRL-treated macrophages was assessed using microscopy, while the response of PRL to MFG-E8 expression was evaluated using luciferase assay. Following treatment with PRL, significant up-regulations of the PRL receptor and MFG-E8 were observed in macrophages, though PRL-treated macrophages more efficiently engulfed apoptotic cells. The results of MFG-E8 promoter analysis showed considerable up-regulation of promoter activity in macrophages following PRL treatment and results from mutation analysis of the MFG-E8 promoter suggested that the C/EBPβ binding site was responsible for PRL-induced activation of the MFG-E8 promoter. C/EBPβ activity was found to be up-regulated in PRL-treated cells as revealed by an electrophoretic mobility shift assay (EMSA). In conclusion, PRL is a potent inducer of MFG-E8 expression in macrophages, while its effect is mediated by the presence of a responsive element in the MFG-E8 promoter.     

Consistency principle in biological dynamical systems

We propose a principle of consistency between different hierarchical levels of biological systems. Given a consistency between molecule replication and cell reproduction, universal statistical laws on cellular chemical abundances are derived and confirmed experimentally. They include a power law distribution of gene expressions, a lognormal distribution of cellular chemical abundances over cells, and embedding of the power law into the network connectivity distribution. Second, given a consistency between genotype and phenotype, a general relationship between phenotype fluctuations by genetic variation and isogenic phenotypic fluctuation by developmental noise is derived. Third, we discuss the chaos mechanism for stem cell differentiation with autonomous regulation, resulting from a consistency between cell reproduction and growth of the cell ensemble.

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A generic mechanism for adaptive growth rate regulation

How can a microorganism adapt to a variety of environmental conditions despite the existence of a limited number of signal transduction mechanisms? We show that for any growing cells whose gene expression fluctuate stochastically, the adaptive cellular state is inevitably selected by noise, even without a specific signal transduction network for it. In general, changes in protein concentration in a cell are given by its synthesis minus dilution and degradation, both of which are proportional to the rate of cell growth. In an adaptive state with a higher growth speed, both terms are large and balanced. Under the presence of noise in gene expression, the adaptive state is less affected by stochasticity since both the synthesis and dilution terms are large, while for a nonadaptive state both the terms are smaller so that cells are easily kicked out of the original state by noise. Hence, escape time from a cellular state and the cellular growth rate are negatively correlated. This leads to a selection of adaptive states with higher growth rates, and model simulations confirm this selection to take place in general. The results suggest a general form of adaptation that has never been brought to light—a process that requires no specific mechanisms for sensory adaptation. The present scheme may help explain a wide range of cellular adaptive responses including the metabolic flux optimization for maximal cell growth.