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BMC Biol,
2012]
The dramatic ingression of tissue sheets that accompanies many morphogenetic processes, most notably gastrulation, has been largely attributed to contractile circum-apical actomyosin 'purse-strings' in the infolding cells. Recent studies, however, including one in BMC Biology, expose mechanisms that rely less on actomyosin contractility of purse-string bundles and more on dynamics in the global cortical actomyosin network of the cells. These studies illustrate how punctuated actomyosin contractions and flow of these networks can remodel both epithelial and planarly organized mesenchymal sheets.
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Development,
1990]
Embryonic processes in the nematode C. elegans, the gastropod mollusc Ilyanassa, the dipteran Drosophila, the echinoid Strongylocentrotus purpuratus, the ascidian Ciona, the anuran Xenopus, the teleost Brachydanio and mouse are compared with respect to a series of parameters such as invariant or variable cleavage, the means by which the embryonic axes are set up, egg anisotropies and reliance on conditional or on autonomous specification processes. A molecular interpretation of these modes of specification of cell fate in the embryo is proposed, in terms of spatial modifications of gene regulatory factors. On this basis, classically defined phenomena such as regulative development and cytoplasmic localization can be interpreted at a mechanistic level, and the enormous differences between different forms of embryogenesis in the Animal Kingdom can be considered within a common mechanistic framework. Differential spatial expression of histospecific genes is considered in terms of the structure of the gene regulatory network that will be required in embryos that utilize cell-cell interaction, autonomous vs conditional specification and maternal spatial information to differing extents. It is concluded that the regulatory architectures according to which the programs of gene expression are organized are special to each form of development, and that common regulatory principles are to be found only at lower levels, such as those at which the control regions of histospecific structural genes operate.
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J Exp Zool,
1999]
A memorable workshop, focused on causal mechanisms in metazoan evolution and sponsored by NASA, was held in early June 1998, at MBL. The workshop was organized by Mike Levine and Eric H. Davidson, and it included the PI and associates from 12 different laboratories, a total of about 30 people. Each laboratory had about two and one half hours in which to represent its recent research and cast up its current ideas for an often intense discussion. In the following we have tried to enunciate some of the major themes that emerged, and to reflect on their implications. The opinions voiced are our own. We would like to tender apologies over those contributions we have not been able to include, but this is not, strictly speaking, a meeting review. Rather we have focused on those topics that bear more directly on evolutionary mechanisms, and have therefore slighted some presentations (including some of our own), that were oriented mainly toward developmental processes. J. Exp. Zool. (Mol. Dev. Evol. ) 285:104-115, 1999.
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Curr Opin Genet Dev,
2021]
Homologous recombination (HR) plays a critical role in largely error-free repair of mitotic and meiotic DNA double-strand breaks (DSBs). DSBs are one of the most deleterious DNA lesions, which are repaired by non-homologous end joining (NHEJ), homologous recombination (HR) or, if compromised, micro-homology mediated end joining (MMEJ). If left unrepaired, DSBs can lead to cell death or if repaired incorrectly can result in chromosome rearrangements that drive cancer development. Here, we describe recent advances in the field of mitotic HR made using Caenorhabditis elegans roundworm, as a model system.
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International Review of Cytology,
1986]
The problem of cell-specific gene expression has long been a major concern to developmental biologists. Why and how specific genes are expressed only in certain differentiated cells and not in others are of vital importance. Many well-documented examples of differentiated cell types expressing quantitative and/or qualitative changes in gene expression now exist. For example, Galau et al. (1976) demonstrated that different sets of genes are expressed during development and in different adult tissues of the sea urchin. More recently, Angerer and Davidson (1984) have used in situ hybridization of specific DNA probes to demonstrate the expression of lineage-specific genes long before morphological differentiation. Other examples include the ovalbumin gene, known to be expressed only in hormone-stimulated oviducts, and the globin genes expressed at various developmental stages in differentiating erythrocytes. Many other examples of cell-specific gene expression are known, including the silk moth chorion proteins, the glue proteins in Drosophila, and a-amylase in mammals. Detailed molecular analysis of genes has provided important information on the mechanisms of gene expression. For example, numerous studies have examined the role of chromatin structure as well as the significance of specific sequences in the transcription and translation of eukaryotic genes. Furthermore, studies of the globin, actin, immunoglobulin, histone, and silk moth chorion genes have demonstrated the existence of gene families with suggested importance for the evolution of new functions for old genes. In addition, the detailed study of multigene families has provided vital information on the mechanisms of cell-specific gene expression as seen, for example, in the temporal and spatial regulation of different members of the actin gene family....
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Bioessays,
1994]
If treated harshly, any cell can be induced to die. These pathological deaths typically occur by necrosis, a passive process that involves membrane disruption, cellular swelling and ultimately, cellular lysis. Less well appreciated is the observation that many, if not most, of the cells that die during an organism's life, commit suicide. Instead of swelling, these cells become condensed and in most cases, undergo stereotypic changes in their surface and nuclear morphology that has been termed apoptosis . Another feature of most apoptotic deaths, is the double-stranded cleavage of genomic DNA by an endogenous DNAse . Interestingly, not all cells that undergo programmed cell death exhibit these apoptotic
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Cell Motil Cytoskeleton,
2009]
Intermediate filaments (IFs) make up one of the three major fibrous cytoskeletal systems in metazoans. Numerous IF polypeptides are synthesized in cell type-specific combinations suggesting specialized functions. The review concentrates on IFs in the model organism Caenorhabditis elegans which carries great promise to elucidate the still unresolved mechanisms of IF assembly into complex networks and to determine IF function in a living organism. In contrast to Drosophila melanogaster, which lacks cytoplasmic IFs altogether, the nematode genome contains 11 genes coding for cytoplasmic IFs and only a single gene for a nuclear lamin. Its cytoplasmic IFs are expressed in developmentally and spatially defined patterns. As an example we present the case of the intestinal IFs which are abundant in the mechanically resilient endotube, a prominent feature of the C. elegans intestinal terminal web region. This IF-rich structure brings together all three cytoskeletal filaments that are integrated into a coherent entity by the C. elegans apical junction (CeAJ) thereby completely surrounding and stabilizing the intestinal lumen with its characteristic brush border. Concepts on the developmental establishment of the endotube in relation to polarization and its function for maintenance of epithelial integrity are discussed. Furthermore, possible connections of the cytoplasmic cytoskeleton to the nuclear lamin IFs and the importance of these links for nuclear positioning are summarized.
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Science,
2002]
If the last common ancestor of plants and animals was unicellular, comparison of the developmental mechanisms of plants and animals would show that development was independently invented in each lineage. And if this is the case, comparison of plant and animal developmental processes would give us a truly comparative study of development, which comparisons merely among animals, or merely among plants, do not-because in each of these lineages, the fundamental mechanisms are similar by descent. Evidence from studies of developmental mechanisms in both kingdoms, and data from genome-sequencing projects, indicate that development evolved independently in the lineages leading to plants and to animals.
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Sci Aging Knowledge Environ,
2002]
This article reviews key events in the genetic analysis of aging in the worm. The events are presented in the form of a timeline and include landmark papers, key meetings, and the development of important funding agencies. I also speculate on events that might appear in this timeline if this review were written in the distant future.
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Microbes Infect,
2002]
If one is interested in dissecting the complex interactions that exist between host and pathogen, the nematode worm Caenorhabditis elegans is perhaps not the first model host that comes to mind. In this review I will introduce 'the worm' and try to show how it is, in fact, well suited to the identification of universal virulence factors and holds great promise for the study of conserved mechanisms of innate immunity.