How to characterize meiotic functions in plants?

Our understanding of plant meiosis is rapidly increasing thanks to the model Arabidopsis thaliana. Here we present the results of a screening for meiotic mutants carried out with a library containing 30,719 T-DNA insertion lines. An average of one mutant per 1000 lines was recovered. Several phenotypic classes could be distinguished and are presented. In parallel, 39 proteins known to be involved in meiosis in non-plant organisms were chosen and a search was performed for homologue sequences in the completed Arabidopsis thaliana genome. Approximately 30% of the meiotic related sequences showed similarities with one or several Arabidopsis putative genes. The relevance of forward versus reverse genetics in order to characterize meiotic functions is discussed.     

How does Cryptococcus get its coat?

During the past few decades, increasing attention has focused on pathogenic fungi both as fascinating research subjects and as the agents of serious illness in diverse patient populations. In particular, opportunistic fungi such as Cryptococcus neoformans command notice as the ranks of their immunocompromised victims grow. C. neoformans is unique among fungal pathogens for its major virulence factor, a complex polysaccharide capsule. In this article, our current understanding of the structure and biosynthesis of the capsule is reviewed, as are the many questions that remain to be answered about how Cryptococcus gets its coat.     

How does a millimeter-sized cell find its center?

Microtubules play a central role in centering the nucleus or mitotic in eukaryotic cells. However, despite common use of microtubules for centering, physical mechanisms can vary greatly, and depend on cell size and cell type. In the small fission yeast cells, the nucleus can be centered by pushing forces that are generated when growing microtubules hit the cell boundary. This mechanism may not be possible in larger cells, because the compressive force that microtubules can sustain are limited by buckling, so maximal force decreases with microtubule length. In a well-studied intermediate sized cell, the C. elegans fertilized egg, centrosomes are centered by cortex-attached motors that pull on microtubules. This mechanism is widely assumed to be general for larger cells. However, re-evaluation of classic experiments in a very large cell, the fertilized amphibian egg, argues against such generality. In these large eggs, movement of asters away from a part of the cell boundary that they are touching cannot be mediated by cortical pulling, because the astral microtubules are too short to reach the opposite cell boundary. A century ago, Herlant and Brachet discovered that multiple asters within a single egg center relative to the cell boundary, but also relative to each other. Here, we summarize current understanding of microtubule organization during the first cell cycle in a fertilized Xenopus egg, discuss how microtubule asters move towards the center of this very large cell, and how multiple asters shape and position themselves relative to each other.     

How does the genetic assassin select its neuronal target?

Through many different routes of analysis, including human familial studies and animal models, we are identifying an increasing number of genes that are causative for human neurodegenerative disease and are now in a position for many such disorders to dissect the molecular pathology that gives rise to neuronal death. Yet a paradox remains: The majority of the genes identified cause neurodegeneration in specific neuronal subtypes, but the genes themselves are ubiquitously expressed. Furthermore, the different mutations in the same gene may cause quite different types of neurodegeneration. Something in our understanding of neurodegenerative disease is clearly missing, and we refer to this as the phenomenon of ??neuronal targeting.?? Here we discuss possible explanations for neuronal targeting, why specific neuronal subtypes are vulnerable to specific mutations in ubiquitously expressed genes.     

How does a bacterium grow during its cell cycle?

Rod-shaped bacteria such as Escherichia coli and Bacillus subtilis appear to extend continuously in length between divisions. However, the kinetics of growth of the individual cell in the steady state is still unknown. A brief, critical account of the main approaches used to determine the pattern of surface extension is given. In general, these approaches are of three types. Firstly, attempts have been made to relate average cell size to growth rate of the culture and to determine possible stages in the cell cycle at which the rate of length extension might change. Secondly, comparisons have been made between the measured length distribution of cells and theoretical distributions, based on three primary hypotheses (linear, bilinear and exponential growth). Thirdly, the principle of Collins and Richmond, involving the calculation of growth rate from the length distributions of extant, separating and new-born cells, is described. It is emphasized that there is a strong element of variation in size at different stages of the cell cycle. This variation imposes severe limitations on models which utilize only average cellular dimensions. We conclude that the Collins-Richmond principle affords the most powerful approach to the analysis of bacterial growth kinetics. However, we propose that the method be modified to permit calculation of separate rates of growth of cells between discernible events in the cell cycle, as well as simply between birth and division.     

How does parkin ligate ubiquitin to Parkinson's disease?

Recessive mutations in the human PARKIN gene are the most common cause of hereditary parkinsonism, which arises from the degeneration of dopaminergic neurons in the substantia nigra. However, the molecular mechanisms by which the loss of parkin causes dopaminergic neurodegeneration are not well understood. Parkin is an enzyme that ubiquitinates several candidate substrate proteins and thereby targets them for proteasomal degradation. Hypothesis-driven searches have led to the discovery of aggregation-prone protein substrates of parkin. Moreover, the enzyme is upregulated when under unfolded protein stress. Thus, loss-of-function mutations of parkin might impair the removal of potentially toxic protein aggregates. However, the limited neuropathological information that is available from parkin-proven patients, as well as the recent knockout of the parkin gene in fruit flies and mice, may indicate a more complex disease mechanism, possibly involving the misfolding of parkin itself or of additional substrates. The risk factors that predispose dopaminergic neurons to degenerate on parkin failure are yet to be identified.     

How and why does the proteome respond to microgravity?

For medical and biotechnological reasons, it is important to study mammalian cells, animals, bacteria and plants exposed to simulated and real microgravity. It is necessary to detect the cellular changes that cause the medical problems often observed in astronauts, cosmonauts or animals returning from prolonged space missions. In order for in vitro tissue engineering under microgravity conditions to succeed, the features of the cell that change need to be known. In this article, we summarize current knowledge about the effects of microgravity on the proteome in different cell types. Many studies suggest that the effects of microgravity on major cell functions depend on the responding cell type. Here, we discuss and speculate how and why the proteome responds to microgravity, focusing on proteomic discoveries and their future potential.     

How to break recombinant bacteria: does it matter?

Recombinant proteins and other materials of industrial interest produced in?Escherichia coli are usually retained within the bacterial cell, in the cytoplasmic?space, where they have been produced. Different protocols for cell disruption?have been implemented as an initial downstream step, which keeps the?biological and mechanical properties of the process products. Being necessarily?mild, these approaches often result in 95-99% cell disruption, what is more than?acceptable from the yield point of view. However, when the bacterial product?are nano or microparticulate entities that tend to co-sediment with entire?bacterial cells, the remaining undisrupted bacteria appear as abounding?contaminants, making the product not suitable for a spectrum of biomedical?applications. Since bacterial inclusion bodies are now seen as bacterial?materials valuable in different fields, we have developed an alternative cell?disruption protocol that permits obtaining fully bacterial free protein particles,?keeping the conformational status of the embedded proteins and the?mechanical properties of the full aggregates.