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At least 163 records · Page 9Linked to original sources

Self-assembly of structures resembling functional organs by pure populations of cells.

It is proposed that self-assembly of structures resembling organs can occur by virtue of the properties of the component cells alone. This property is derived from regional specializations of the individual component cells, and can arise in pure populations. This kind of self-assembly is distinct from the phenomenon of 'sorting out' of heterogeneous cell populations, to which this description is usually applied. It is associated with the expression of the differentiated state of the cell. Examples are drawn from the formation of blood vessels, muscles, cartilage elements, kidney, and neurectodermal derivatives.

Animals↗

Characterization of Barmah forest virus: an alphavirus with some unusual properties.

Barmah Forest virus has been characterized in a number of ways including electron microscopy of infected cells; physical studies of the virion, its RNA, and associated proteins; N-terminal sequence analysis of the two envelope glycoproteins; studies of macromolecular species present in infected cells; and serological cross-reactions with alphaviruses and bunyaviruses. From these results Barmah Forest virus is clearly an alphavirus since the structure of the virion, the mode of replication, and the macromolecular species present in infected cells are typical of alphaviruses. The N-terminal regions of the two glycoproteins E1 and E2 show extensive sequence homology (approximately 50%) with those of other alphaviruses. Barmah Forest virus cross-reacts in hemagglutination inhibition tests, although not in complement fixation tests or infectivity neutralization tests, with other alphaviruses. In some of its properties Barmah Forest virus is unusual, however. It cross-reacts in complement fixation and hemagglutination inhibition tests with Umbre virus, a bunyavirus, which originally led it to be classified as a bunyavirus; the glycosylation pattern of E2 of Barmah Forest virus appears to differ from that of other alphaviruses; and the sedimentation coefficient of the virion appears to be slightly less than that of other alphaviruses.

Aedes↗

The role of Xenopus frizzled-8 in pronephric development.

Vertebrates use two or three forms of kidney successively during development and the nephric duct is essential for this succession of kidney induction. While transcripts of many Wnt ligands and Wnt receptor Frizzled genes have been localized in developing kidney, the relationship between Wnt signaling and nephric duct development remains unknown. This study investigated the role of Xenopus frizzled-8 (Xfz8) in pronephros development. Translational inhibition of Xfz8 caused a significant reduction in the staining of a duct-specific antibody, but did not affect the expression of early pronephric maker genes in the duct region. Defects in pronephric tubule branching were also observed following inhibition of Xfz8. Histological analysis revealed that the Xfz8-inhibited cells failed to form a normal epithelium structure. These results suggest that Xfz8 is involved in the process of normal epithelium formation in the developing pronephric duct and tubules after specification.

Animals↗

Maternal cold inducible RNA binding protein is required for embryonic kidney formation in Xenopus laevis.

We cloned a major isoform of Xenopus homologue of cold inducible RNA binding protein (CIRP), XCIRP-1. XCIRP-1 was neither cold inducible nor essential for cell division during early embryonic development. Suppression of XCIRP-1 dose dependently produced tailbuds with deformations of the brain and internal organs. The defects were XCIRP-1 specific as they could be rescued by sense transcript. Suppression of XCIRP-1 also disrupted the morphogenetic migration of the C3 blastomeres (lineaged to become the embryonic kidney, the pronephros). In animal cap explants, depletion of XCIRP-1 inhibited activin/retinoic acid induced expressions of pronephros related Xlim-1 and WT1 genes. These results suggest that XCIRP-1 is required for the specification and morphogenetic lineage migration of the pronephros.

Abnormalities, Multiple↗

The role of the activin-follistatin system in the developmental and regeneration processes of the kidney.

Regeneration processes in many tissues are modulated by various factors, which are involved in their organogenesis. Activin A, a member of the TGF-beta superfamily, inhibits branching tubulogenesis of the kidney in organ culture system as well as in in vitro tubulogenesis model. On the other hand, follistatin, an antagonist activin A, reverses the effect of activin A on kidney development, induces branching tubulogenesis, and also promotes tubular regeneration after ischemia/reperfusion injury by blocking the action of endogenous activin A. The activin-follistatin system is one of the important regulatory systems modulating developmental and regeneration processes of the kidneys.

Activins↗

Ligand-activated Ahr signaling leads to disruption of nephrogenesis and altered Wilms' tumor suppressor mRNA splicing.

The aryl hydrocarbon receptor (Ahr), a member of the large basic helix-loop-helix (bHLH) and PAS homology domain superfamily, is a highly conserved transcriptional regulator involved in mammalian development. In the present study, a murine metanephros organ culture system was employed to evaluate the role of the Ahr signaling in nephrogenesis in vitro. Ahr and Wilms' tumor suppressor (wt1) mRNAs were detected by in situ hybridization and RT-PCR during the course of renal development. Treatment with 3 microM BaP, a hydrocarbon ligand of Ahr, inhibited glomerulogenesis and branching morphogenesis of metanephric kidneys. Deficits in the epithelialization of mesenchymal cells were evidenced by inhibition of the formation of podocyte foot processes and glomerular basement membranes. Hydrocarbon treatment markedly induced -KTS wt1 splice variants, although total wt1 mRNA levels remained unchanged. A significant decrease in total WT1 protein was observed by both immunocytochemistry and Western analysis in cultures challenged with BaP compared to controls. Comparison of metanephric cultures from Ahr+/+ and Ahr-/- mice showed that Ahr is involved in kidney development, and required for BaP-induced deficits in nephrogenesis. These results indicate that ligand activation of Ahr signaling disrupts nephrogenesis in vitro, and that this response involves modulation of wt1 alternative splicing and post-transcriptional control.

Alternative Splicing↗

Roles of kringle domain-containing serine proteases in epithelial-mesenchymal transitions during embryonic development.

Transformation of an epithelial sheet into a migrating mesenchymal cell population implies the destruction of the basal lamina underlying the epithelium, and the subsequent localized digestion of the extracellular matrix by the migrating cells. Proteases are involved in these processes. Among them, molecules containing both a serine protease domain and at least one kringle domain have been identified as possible important effectors. Interestingly, related proteins containing an inactive serine protease domain also seem to play a role, suggesting that the function of these molecules in epithelial-mesenchymal transformation is not confined to proteolytic digestion of cell attachments. Instead, these molecules act through specific tyrosine kinase receptors in the membrane of the responding cells. In this review, we summarize data implicating this family of molecules in various epithelial-mesenchymal transitions during embryonic development. Our major focus of attention are: hepatocyte growth factor/scatter factor (HGF/SF), its tyrosine kinase receptor proto-oncogene c-met, and the related peptide factor HGF-like/macrophage-stimulating protein (HGF1/MSP), whose receptor is the Ron tyrosine kinase. c-met and Ron also have another close homolog in the chick, called Sea, whose ligand remains unknown. Interestingly, HGF/SF is activated by other plasminogen-related molecules which, apart from a specific activator, include the protease urokinase. HGF/SF, c-met and HGF/MSP are expressed in dynamic ways during early embryonic development, correlating with regions undergoing epithelial/mesenchymal transformations. Moreover, several assays are now starting to reveal great pleiotropism of function during development, including both the loss and the acquisition of epithelial morphology according to the cell type and assay used, as well as angiogenesis, kidney tubule morphogenesis, cell motility, the maintenance of competence for neural induction and some aspects of the later development of the musculoskeletal and nervous systems.

Animals↗

Rubella virus maturation and production in two host cell systems.

When inoculated at the same MOI, Vero cells released a larger amount of infectious rubella virus into the culture medium than did BHK21 cells, However, BHK21 cells (in monolayer or in suspension) produced more intracellular infectious virus than Vero cells when tested 24 h after infection. Maturation of the virus in BHK21 cells occurred at the plasma membrane and, in a larger quantity, in the cytoplasm (Golgi apparatus and vacuoles). Viral particles consisted of an electron-dense core (32 nm) surrounded by a capsid and enveloped by a single membrane (8-10 nm). Aberrant forms (elongated and twisted) in the vacuole and double virions in the plasma membrane were observed as early as 65 h after infection.

Animals↗

The problem of sampling homologous groups of nephrons during development of the chick mesonephros.

With the aim of defining homologous groups of nephrons in the chick mesonephros at different stages of development, we opened the abdominal wall of 295 White Leghorn embryos at stage HH 26 and marked off 6 segments of equal length at different levels of the organ by Seichert's plastic linear marking method (Seichert 1965), using marks previously introduced into the vertebral column at the same levels as a guide. The embryos were removed after 2-6 days, weighed and classified according to weight. The primordia of the marked vertebrae were identified. The length of the artificially defined segments or their relationships to both poles of the mesonephros were evaluated in projections. The portion of the mesonephros above Th 3 level shorten during the period of observation, while the more caudal segments grow in a craniocaudal gradient. Homologous groups of nephrons can be identified only by the marking technique, except for those at Th 7 level, whose distance from the caudal pole does not alter up to the 11th embryonic day.

Animals↗

Glial line-derived neurotrophic factor (GDNF): Biological activities.

Glial cell line-derived neurotrophic factor (GDNF) was initially discovered as a neurotrophic factor that enhances survival of midbrain dopaminergic neurons. Findings in 1994 and 1995 extended the spectrum of biological activities of GDNF to different populations of neurons (motor and sensory). Recent findings revealed that GDNF, Neurturin (NTN), Persephin (PSP), and Artemin (ARTN) are members of the GDNF protein family and are structurally related to transforming growth factor protein family. They are survival factors for peripheral and central neurons, for oligodendrocytes and can promote morphogenesis of kidney in vitro.

Glial Cell Line-Derived Neurotrophic Factor↗