Feast or famine

Lysosomal storage diseases are metabolic disorders characterized by the accumulation of acidic vacuoles, and are usually the consequence of the deficiency of an enzyme responsible for the metabolism of vesicular lipids, proteins or carbohydrates. In contrast, mucolipidosis type IV (MLIV), results from the absence of a vesicular Ca²⁺ release channel called mucolipin 1/transient receptor potential mucolipin 1 (MCOLN1/TRPML1) which is required for the fusion of amphisomes with lysosomes. In Drosophila, ablation of the MCOLN1 homolog (trpml) leads to diminished viability during pupation when the animals rely on autophagy for nutrients. This pupal lethality results from decreased target of rapamycin complex 1 (TORC1) signaling, and is reversed by reactivating TORC1. Our findings indicate that one of the primary causes of toxicity in the absence of TRPML is cellular amino acid starvation, and the resulting decrease in TORC1 activity. Furthermore, our findings raise the intriguing possibility that the neurological dysfunction in MLIV patients may arise from amino acid deprivation in neurons. Therefore, future studies evaluating the levels of amino acids and TORC1 activity in MLIV neurons may aid in the development of novel therapeutic strategies to combat the severe manifestations of MLIV.     

Feast and famine in plant genomes

Plant genomes vary over several orders of magnitude in size, even among closely related species, yet the origin, genesis and significance of this variation are not clear. Because DNA content varies over a sevenfold range among diploid species in the cotton genus (Gossypium) and its allies, this group offers opportunities for exploring patterns and mechanisms of genome size evolution. For example, the question has been raised whether plant genomes have a one-way ticket to genomic obesity, as a consequence of retroelement accumulation. Few empirical studies directly address this possibility, although it is consistent with recent insights gleaned from evolutionary genomic investigations. We used a phylogenetic approach to evaluate the directionality of genome size evolution among Gossypium species and their relatives in the cotton tribe (Gossypieae, Malvaceae). Our results suggest that both DNA content increase and decrease have occurred repeatedly during evolution. In contrast to a model of unidirectional genome size change, the frequency of inferred genome size contraction exceeded that of expansion. In conjunction with other evidence, this finding highlights the dynamic nature of plant genome size evolution, and suggests that poorly understood genomic contraction mechanisms operate on a more extensive scale that previously recognized. Moreover, the research sets the stage for fine-scale analysis of the evolutionary dynamics and directionality of change for the full spectrum of genomic constituents.     

Feast or famine: the host–pathogen battle over amino acids

Intracellular bacterial pathogens often rely on their hosts for essential nutrients. Host cells, in turn, attempt to limit nutrient availability, using starvation as a mechanism of innate immunity. Here we discuss both host mechanisms of amino acid starvation and the diverse adaptations of pathogens to their nutrient‐deprived environments. These processes provide both key insights into immune subversion and new targets for drug development.     

Feast/famine growth environments and activated sludge population selection

The effect of feast/famine growth conditions on activated sludge cultures indicates that nonfilamentous cultures can be selected by providing proper substrate gradients and extended periods of endogenous metablism. Reactor operating strategies providing intermittently high substrate concentrations result in cultures characterized by high peak substrate and oxygen uptake activities, rapid settling rates, and high resistance to starvation. Sludge settleability can be manipulated using controlled variations in growth environment with corresponding changes noted in sludge activity. In combination with the low net growth rates associated with activated sludge systems, feast/famine environments would logically convey a selection advantage to microbes capable of readily assimilating substrate materials and maintaining viability during extended starvation periods.     

Feast or famine for intertidal grazing molluscs: a mis-match between seasonal variations in grazing intensity and the abundance of microbial resources

Distinct seasonal variations in the abundance of photosynthetic microbiota and limpet grazing intensity were recorded at Port St Mary, Isle of Man between January 1994 and June 1996. Microbial abundance was negatively correlated with insolation stress, while grazing intensity was positively correlated with sea and air temperature. These patterns result in a mis-match between the supply of and the demand for microbial resources with maximal grazing intensity during the summer and autumn, but maximal microbial standing stock during the winter and early spring. The importance of top-down control of microbial assemblages by grazing was demonstrated by experimental exclusion of limpets during autumn 1993. This resulted in a four-fold increase in the abundance of cyanobacteria within 6 days, followed by a more gradual proliferation of ephemeral algae during the next 4 weeks. The abundance of diatoms remained relatively constant and was not influenced by the removal of grazers at this time of year. The influence of microbial resource availability on the growth and mortality of limpets was examined using experimental enclosures of differing densities of either Patella vulgata or P. depressa. After 6 months, there were significant relationships between grazer density and both mortality and growth with increased mortality and reduced growth for P. vulgata at increased densities, and reduced growth for P. depressa at increased densities. Hence, the availability of microbial resources may also influence the biomass of grazers on rocky shores from the bottom upwards. A conceptual model is presented which describes seasonal and annual variations in microbial resources and grazing intensity and their potential consequences for other shore dwellers.     

Mammalian cell culture: engineering principles and scale-up

If biological products such as monoclonal antibodies, interferons, vaccines, plasminogen activators and many others are to be obtained at an economic cost from mammalian cells, a number of engineering problems must be solved (Tables 1 and 2). The two most imposing barriers to the scale-up of this technology from those listed are the inability to provide sufficient oxygen to high density cultures of mammalian cells grown in large volumes, and the high cost of serum usage. This review focuses on: (i) techniques used to cultivate mammalian cells; (ii) technical barriers to scale-up; and (iii) comparing methods of producing cells with regards to their ability to overcome these barriers.     

Cell death in mammalian cell culture: molecular mechanisms and cell line engineering strategies

Cell death is a fundamentally important problem in cell lines used by the biopharmaceutical industry. Environmental stress, which can result from nutrient depletion, by-product accumulation and chemical agents, activates through signalling cascades regulators that promote death. The best known key regulators of death process are the Bcl-2 family proteins which constitute a critical intracellular checkpoint of apoptosis cell death within a common death pathway. Engineering of several members of the anti-apoptosis Bcl-2 family genes in several cell types has extended the knowledge of their molecular function and interaction with other proteins, and their regulation of cell death. In this review, we describe the various modes of cell death and their death pathways at molecular and organelle level and discuss the relevance of the growing knowledge of anti-apoptotic engineering strategies to inhibit cell death and increase productivity in mammalian cell culture.     

Historical reflections on cell culture engineering

Cell culture engineering has enabled the commercial marketing of about a dozen human therapeutic products derived from rDNA technology and numerous monoclonal antibody products as well. A variety of technologies have proven useful in bringing products to the marketplace. Comparisons of the technologies available 15 years ago are contrasted with those available today. A number of improvements in unit operations have greatly improved the robustness of the processes during the past 15 years. Further evolution of the technology is expected in several directions driven by commercial and regulatory pressures. Some problems remain for the next generation of cell culture engineers to solve. This revised version was published online in August 2006 with corrections to the Cover Date.     

Production and engineering of terpenoids in plant cell culture

Terpenoids are a diverse class of natural products that have many functions in the plant kingdom and in human health and nutrition. Their chemical diversity has led to the discovery of over 40,000 different structures, with several classes serving as important pharmaceutical agents, including the anticancer agents paclitaxel (Taxol) and terpenoid-derived indole alkaloids. Many terpenoid compounds are found in low yield from natural sources, so plant cell cultures have been investigated as an alternate production strategy. Metabolic engineering of whole plants and plant cell cultures is an effective tool to both increase terpenoid yield and alter terpenoid distribution for desired properties such as enhanced flavor, fragrance or color. Recent advances in defining terpenoid metabolic pathways, particularly in secondary metabolism, enhanced knowledge concerning regulation of terpenoid accumulation, and application of emerging plant systems biology approaches, have enabled metabolic engineering of terpenoid production. This paper reviews the current state of knowledge of terpenoid metabolism, with a special focus on production of important pharmaceutically active secondary metabolic terpenoids in plant cell cultures. Strategies for defining pathways and uncovering rate-influencing steps in global metabolism, and applying this information for successful terpenoid metabolic engineering, are emphasized.     

微重力条件下细胞培养和组织工程研究进展

随着空间生命科学研究的发展,人们将细胞、组织培养技术与微重力环境相结合产生了组织工程研究的一个新领域——微重力组织工程。模拟微重力条件下细胞培养和组织构建研究表明,微重力环境有利于细胞的三维生长,形成具有功能的组织样结构,培养后的三维组织无论从形态上还是基因表达上都更接近于正常的机体组织。这种微重力对细胞的作用效应,将可能为未来组织工程和再生医学研究提供一条新途径。该文概述了近十年来国内外微重力组织工程相关研究的最新进展。     

Evolution of networks and sequences in eukaryotic cell cycle control

The molecular networks regulating the G1-S transition in budding yeast and mammals are strikingly similar in network structure. However, many of the individual proteins performing similar network roles appear to have unrelated amino acid sequences, suggesting either extremely rapid sequence evolution, or true polyphyly of proteins carrying out identical network roles. A yeast/mammal comparison suggests that network topology, and its associated dynamic properties, rather than regulatory proteins themselves may be the most important elements conserved through evolution. However, recent deep phylogenetic studies show that fungal and animal lineages are relatively closely related in the opisthokont branch of eukaryotes. The presence in plants of cell cycle regulators such as Rb, E2F and cyclins A and D, that appear lost in yeast, suggests cell cycle control in the last common ancestor of the eukaryotes was implemented with this set of regulatory proteins. Forward genetics in non-opisthokonts, such as plants or their green algal relatives, will provide direct information on cell cycle control in these organisms, and may elucidate the potentially more complex cell cycle control network of the last common eukaryotic ancestor.