Mechanisms and in vivo functions of contact inhibition of locomotion

Contact inhibition of locomotion (CIL) is a process whereby a cell ceases motility or changes its trajectory upon collision with another cell. CIL was initially characterized more than half a century ago and became a widely studied model system to understand how cells migrate and dynamically interact. Although CIL fell from interest for several decades, the scientific community has recently rediscovered this process. We are now beginning to understand the precise steps of this complex behaviour and to elucidate its regulatory components, including receptors, polarity proteins and cytoskeletal elements. Furthermore, this process is no longer just in vitro phenomenology; we now know from several different in vivo models that CIL is essential for embryogenesis and in governing behaviours such as cell dispersion, boundary formation and collective cell migration. In addition, changes in CIL responses have been associated with other physiological processes, such as cancer cell dissemination during metastasis

Die Verteilung der loeslichen lytischen Transglycosylase in Escherichia coli und ihre Rolle bei der Bakterienlyse durch den Phagen MS2 Elektronenmikroskopische und physiologische Untersuchungen

Available from TIB Hannover: DW 3502 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Subcellular distribution of the soluble lytic transglycosylase in Escherichia coli.

The localization of the major autolytic enzyme, the soluble lytic transglycosylase, in the different cell compartments of Escherichia coli was investigated by immunoelectron microscopy. Ultrathin sections were labeled with a specific antiserum against purified soluble lytic transglycosylase, and the antibody-enzyme complexes were visualized with colloidal protein A-gold. A preferential localization of the lytic transglycosylase in the envelope was observed, with only 20 to 30% of the enzyme left in the cytoplasm. Most of the enzyme associated with the cell wall was tightly bound to the murein sacculus. Sacculi prepared by boiling of cells in 4% sodium dodecyl sulfate could be immunolabeled with the specific antiserum, indicating a surprisingly strong interaction of the lytic transglycosylase with murein. The enzyme-substrate complex could be reconstituted in vitro by incubating pronase-treated, protein-free murein sacculi with purified lytic transglycosylase at 0 degrees C. Titration of sacculi with increasing amounts of enzyme indicated a limiting number of binding sites for about 1,000 molecules of enzyme per sacculus. Ruptured murein sacculi obtained after penicillin treatment revealed that the enzyme is exclusively bound to the outer surface of the sacculus. This finding is discussed in the light of recent evidence suggesting that the murein of E. coli might be a structure of more than one layer expanding by inside-to-outside growth of patches of murein

Homotypic cell competition regulates proliferation and tiling of zebrafish pigment cells during colour pattern formation

The adult striped pattern of zebrafish is composed of melanophores, iridophores and xanthophores arranged in superimposed layers in the skin. Previous studies have revealed that the assembly of pigment cells into stripes involves heterotypic interactions between all three chromatophore types. Here we investigate the role of homotypic interactions between cells of the same chromatophore type. Introduction of labelled progenitors into mutants lacking the corresponding cell type allowed us to define the impact of competitive interactions via long-term in vivo imaging. In the absence of endogenous cells, transplanted iridophores and xanthophores show an increased rate of proliferation and spread as a coherent net into vacant space. By contrast, melanophores have a limited capacity to spread in the skin even in the absence of competing endogenous cells. Our study reveals a key role for homotypic competitive interactions in determining number, direction of migration and individual spacing of cells within chromatophore populations

Local reorganization of xanthophores fine-tunes and colors the striped pattern of zebrafish

The pattern of alternating blue and golden stripes displayed by adult zebrafish is composed of three kinds of pigment cells: black melanophores, yellow xanthophores, and silvery-blue iridophores. We analyzed the dynamics of xanthophores during stripe morphogenesis in vivo with long-term time-lapse imaging. Larval xanthophores start to proliferate at the onset of metamorphosis and give rise to adult xanthophores covering the flank before the arrival of stem-cell-derived iridophores and melanophores. Xanthophores compact to densely cover the iridophores forming the interstripe, and they acquire a loose stellate shape over the melanophores in the stripes. Thus, xanthophores, attracted by iridophores and repelling melanophores, sharpen and color the pattern. Variations on these cell behaviors may contribute to the generation of color pattern diversity in fish

Genetic Analysis of Adenohypophysis Formation in Zebrafish

The adenohypophysis consists of at least six different cell types, somatotropes, lactotropes, thyrotropes, melanotropes, corticotropes, and gonadotropes. In mouse, cloning of spontaneous mutations and gene targeting has revealed multiple genes required for different steps of adenohypophysis development. Here, we report the results of a systematic search for genes required for adenohypophysis formation and patterning in zebrafish. By screening F3 offspring of N-ethyl-N-nitrosourea-mutagenized founder fish, we isolated eleven mutants with absent or reduced expression of GH, the product of somatotropes, but a normally developing hypothalamus. Of such mutants, eight were further analyzed and mapped. They define four genes essential for different steps of adenohypophysis development. Two of them, lia and pia, affect the entire adenohypophysis, whereas the other two are required for a subset of adenohypophyseal cell types only. The third gene is zebrafish pit1 and is required for lactotropes, thyrotropes, and somatotropes, similar to its mouse ortholog, whereas the fourth, aal, is required for corticotropes, melanotropes, thyrotropes, and somatotropes, but not lactotropes. In conclusion, the isolated zebrafish mutants confirm principles of adenohypophysis development revealed in mouse, thereby demonstrating the high degree of molecular and mechanistic conservation among the different vertebrate species. In addition, they point to thus far unknown features of adenohypophysis development, such as the existence of a new lineage of pituitary cells, which partially overlaps with the Pit1 lineage. Positional cloning of the lia, pia, and aal genes might reveal novel regulators of vertebrate pituitary development

Conserved Functions of Ikaros in Vertebrate Lymphocyte Development: Genetic Evidence for Distinct Larval and Adult Phases of T Cell Development and Two Lineages of B Cells in Zebrafish

Zebrafish has been advocated as an alternative animal model to study lymphocyte development, although the similarities in the genetic requirements of lymphopoiesis between fish and mammals have not yet been investigated. In this study, we examine the role of the transcription factor Ikaros in zebrafish lymphopoiesis. In fish larvae homozygous for an ikaros allele predicted to lack the C-terminal zinc fingers, T lymphopoiesis is absent; the presence of VHDμJμ rearrangements in adolescent fish is delayed in mutants. In adolescent mutant fish, T cells expressing tcrb and tcrd and B cells expressing igm are formed with low efficiency and display an oligoclonal Ag receptor repertoire. By contrast, B cells expressing the igz isotype do not develop, providing genetic evidence for two separate B cell lineages in zebrafish. Thus, Ikaros appears to play similar roles in fish and mammalian lymphopoiesis