A transmission and scanning electron microscope study of primary neural induction

Summary Normal primary neural induction has been further studied by TEM and SEM. A single mesoderm cell is usually in contact with several ectoderm cells. The mesoderm cells are also contacting other mesoderm cells. It is suggested that ectoderm cells are induced in groups and that induction is synchronized by these contacts. At the points of contact between mesoderm and ectoderm cells cytoplasmic changes are present in the induced tissue.Acknowledgments. M. A. E. would like to thank Prof.F. Beck in whose department this work was conducted. An especial acknowledgment to Mr.Jeff Smith for technical assistance.S. V. C. would like to thank Prof.R. P. Dale in whose department the SEM photographs were prepared.     

Primary neural induction as studied by scanning electron microscopy.

Normal primary neural induction has been studied by scanning electron microscopy and the results compared with those obtained by TEM. Mesoderm cells are usually in contact with several other cells, both mesodermal and endodermal in origin. By SEM the ectoderm layer has been shown to be in contact with the underlying mesoderm cells. Tufts of fibrous basement membrane are also present between the two cell types. TEM specimens also show an intermediate basement membrane.     

Primary neural induction as studied by scanning electron microscopy

Summary Normal primary neural induction has been studied by scanning electron microscopy and the results compared with those obtained by TEM. Mesoderm cells are usually in contact with several other cells, both mesodermal and endodermal in origin. By SEM the ectoderm layer has been shown to be in contact with the underlying mesoderm cells. Tufts of fibrous basement membrane are also present between the two cell types. TEM specimens also show an intermediate basement membrane.Acknowledgments. M. A. E. would like to thank ProfessorF. Beck in whose department this work was conducted. An especial acknowledgment to Mrs.Wendy Nugent for her skilled technical assistance in the preparation of the SEM and TEM specimens. Mr.Duncan Boreham, Electron Microscope Unit, University of Leicester kindly offered assistance and advice.S. V. C. would like to thank ProfessorR. P. Dale in whose department the SEM photographs were prepared.     

Alteration of cell shape in the early chick embryo mesoderm by neuraminidase

Summary Living chick embryo mesoderm cells (stages 3 to 5) were exposed to neuraminidase. The mesoderm cells changed shape losing their long thin processes and become like primitive streak cells, with short flat processes. Ruthenium red staining of such treated embryos shows that the surface coat on the mesoderm cells is reduced in thickness. These results show that cell shape in the chick embryo mesoderm is at least partly determined by the thickness and the composition of the surface coat.Acknowledgment. It is a pleasure to thank Professor F. Beck for the facilities of the Department of Anatomy, University of Leicester, and Mr. G. L. C. McTurk of the University of Leicester Scanning Electron Microscope Unit for operating the ISI 60 SEM. Mr Jeff Smith and Mrs Doris Duncan gave us valuable technical assistance and Dr. A. J. Rowe kindly allowed us to use the facilities of the Electron Microscope Unit, University of Leicester School of Biological Sciences, in specimen preparation.     

PPD-induced blastogenesis is auto-regulated by suppressor cells generated in vitro.

Suppressor cell induction can be demonstrated during antigen specific blastogenesis by using the same methods which have shown induction of suppressor cells by Con A. Since suppressor cells are rapidly generated during antigen specific blastogenesis, they must regulate the final level of blastogenesis induced during the seven day in vitro incubation.     

PPD-induced blastogenesis is auto-regulated by suppressor cells generated in vitro

Summary Suppressor cell induction can be demonstrated during antigen specific blastogenesis by using the same methods which have shown induction of suppressor cells by Con A. Since suppressor cells are rapidly generated during antigen specific blastogenesis, they must regulate the final level of blastogenesis induced during the seven day in vitro incubation.Supported by Unites States Public Health Service grants AM-13377 and CA-19266.     

Evidence for changes in cell shape from a 2-dimensional to a 3-dimensional substrate.

Chick embryo mesoderm cells were explanted to culture systems in vivo and in vitro and their subsequent movements were correlated with the external morphology as studied by SEM. In vitro cell movements are exaggerations of normal in vivo movements where a 2-dimensional substrate is encountered rather than a 3-dimensional environment.     

Replication of immune RNA by human lymphoblastoid cells]

Animal immune RNA used for the induction of the human lymphoblastoid cell line LDV/7, induces the appearance of receptor sites on the surface of these cells and the synthesis of specific immunoglobulins which are liberated into the culture medium. Furthermore, RNA has been extracted from these cells, which possesses the same properties of specific cytotoxicity as the RNA used for induction. It is supposed that the immune RNA derepresses specific genes on the genome of the induced cells.     

Degradation by phytohemagglutinin of the antiviral state induced by interferon]

Phytohaemagglutinin (PHA M and P forms), when added to L 929 cells previously treated by murine interferon, degrades the antiviral state and restores virus sensitivity in the cells. This degradation depends on the amount of the lectin, the contact period with the cell and the presence of PHA membrane receptors. The importance of membrane configuration not only in the induction but also in the maintenance of the antiviral state is discussed.     

The battle against immunopathology: infectious tolerance mediated by regulatory T cells

Infectious tolerance is a process whereby one regulatory lymphoid population confers suppressive capacity on another. Diverse immune responses are induced following infection or inflammatory insult that can protect the host, or potentially cause damage if not properly controlled. Thus, the process of infectious tolerance may be critical in vivo for exerting effective immune control and maintaining immune homeostasis by generating specialized regulatory sub-populations with distinct mechanistic capabilities. Foxp3(+) regulatory T cells (T(regs)) are a central mediator of infectious tolerance through their ability to convert conventional T cells into induced regulatory T cells (iT(regs)) directly by secretion of the suppressive cytokines TGF-β, IL-10, or IL-35, or indirectly via dendritic cells. In this review, we will discuss the mechanisms and cell populations that mediate and contribute to infectious tolerance, with a focus on the intestinal environment, where tolerance induction to foreign material is critical.     

Differentiating abilities of avian somatopleural mesoderm

Summary Quail-to-chick grafting experiments were performed on 2-day embryos in order to test the differentiating abilities of the somatopleure. After orthotopic and heterotopic transplantations of different parts of quail somatopleural mesoderm into chick embryos it is demonstrated that avian somatopleural cells differentiate into skeletal elements, smooth muscles, tendons and connective tissues. However, skeletal muscle fibres do not originate from somatopleural cells.Supported by a grant from the Deutsche Forschungsgemeinschaft (Ch 44/3).     

Differentiation of the endodermal epithelium associated with the splanchnic mesoderm]

Allantoic epithelium and epithelium from different levels of the digestive tube of the guail embryo were grafted into chick embryo splanchnopleure so that these epitheliums would come into contact with the mesoderm of the developing host digestive tube at a variety of levels. Under these conditions, the allantoic epithelium develops into an epithelium corresponding to the level of the digestive tube at which it was grafted. By contrast, the presumptive fate of epithelium from the small intestine is not modified by the mesenchyme with which it becomes associated. Mesenchyme from the small intestine, on the other hand, always dictates the type of differentiation in epithelial grafts from other levels of the digestive tube.     

Differentiating abilities of avian somatopleural mesoderm.

Quail-to-chick grafting experiments were performed on 2-day embryos in order to test the differentiating abilities of the somatopleure. After orthotopic and heterotopic transplatations of different parts of quail somatopleural mesoderm into chick embryos it is demonstrated that avian somatopleural cells differentiate into skeletal elements, smooth muscles, tendons and connective tissues. However, skeletal muscle fibres do not originate from somatopleural cells.     

Cardiovascular development: towards biomedical applicability

Investigating the signalling pathways that regulate heart development is essential if stem cells are to become an effective source of cardiomyocytes that can be used for studying cardiac physiology and pharmacology and eventually developing cell-based therapies for heart repair. Here, we briefly describe current understanding of heart development in vertebrates and review the signalling pathways thought to be involved in cardiomyogenesis in multiple species. We discuss how this might be applied to stem cells currently thought to have cardiomyogenic potential by considering the factors relevant for each differentiation step from the undifferentiated cell to nascent mesoderm, cardiac progenitors and finally a fully determined cardiomyocyte. We focus particularly on how this is being applied to human embryonic stem cells and provide recent examples from both our own work and that of others.     

Somatic and germinal chimerism after the intracoelomic graft of quail splanchnic mesoderm to chick embryos]

The splanchnic mesoderm of the genital area can develop in coelomic graftings as soon as it is colonized by the primordial germ cells (stage 15 of H. and H.). Heterospecific associations between Chick and Quail embryos lead to the differentiation of gonads showing more or less pronounced somatic and germinal chimerisms.