Segmentation and the development of the vertebrate nervous system

1. Recent experiments on the development of neural segmentation in chick embryos are reviewed. 2. Segmentation of the spinal peripheral nerves is governed by a subdivision of the somite-derived sclerotome into anterior and posterior halves. Migrating neural crest cells and outgrowing motor axons are confined to the anterior sclerotome as a result, in part, of inhibitory interactions with posterior sclerotome cells. 3. The sclerotomal distribution of certain molecules known to influence growing nerve cells in vitro, namely laminin, fibronectin, N-CAM, N-Cadherin and J1/tenascin/cytotactin, suggest that these molecules play no critical role in determining the preference of nerve cells for anterior sclerotome. 4. Peanut agglutinin (PNA) recognises cell surface-associated components on posterior cells which, when incorporated into liposomes, cause the abrupt collapse of sensory growth cones in vitro. The PNA receptor(s) may be inhibitory for nerve cells in vivo. 5. The chick hindbrain epithelium is segmented early in its development. Each branchiomotor nucleus in the series of cranial nerves V, VII and IX derives from a pair of segments lying in register with an adjacent branchial arch. Neurogenesis of motor and reticular axons begins in alternate segments, suggesting parallels with insect pattern formation.     

Expression of glycoconjugates during development of the vertebrate nervous system

There is increasing evidence that carbohydrate antigens act as cell recognition molecules in the highly organized structure of the nervous system. These carbohydrate antigens may be expressed as glycolipids, glycoproteins or proteoglycans, and in some cases all three forms of these glycoconjugates, expressing identical carbohydrate epitopes, can be detected in a specific brain region. This article summarizes recent studies concerning the expression of glycoconjugates during development of the vertebrate central nervous system. These findings are discussed in association with current models of glycoconjugate function.     

MicroRNAs in vertebrate development

The vertebrate genome contains hundreds of small non-coding 'microRNAs' that have been implicated in controlling the expression of potentially thousands of target genes. Presently, only a handful of these targets have been characterized. Recent reports of microRNA 'sensors', microRNA microarrays and the creation of vertebrates that lack all microRNA activity will aid in determining the roles played by microRNAs, and the genes that they regulate, during vertebrate development.     

Xenopus as a model system for vertebrate heart development

The African clawed frog, Xenopus laevis, is a valuable model system for studies of vertebrate heart development. In the following review, we describe a range of embryological and molecular methodologies that are used in Xenopus research and discuss key discoveries relating to heart development that have been made using this model system. We also discuss how the sequence of the Xenopus tropicalis genome provides a valuable tool for identification of orthologous genes and for identification of evolutionarily conserved promoter elements. Finally, both forward and reverse genetic approaches are currently being applied to Xenopus for the study of vertebrate heart development.     

Bone morphogenetic protein signalling and vertebrate nervous system development

Transforming growth factor-beta (TGFbeta) signalling, particularly signalling from the bone morphogenetic protein (BMP) members of this protein family, is crucial for the development of both the central and peripheral nervous systems in vertebrates. Experimental embryology and genetics performed in a range of organisms are providing insights into how BMPs establish the neural tissue and control the types and numbers of neurons formed. These studies also highlight the interactions between different developmental signals that are necessary to form a functional nervous system. The challenges ahead will be to uncover functions of TGFbeta signalling in later stages of CNS development, as well as to determine possible associations with neurological diseases.     

Interrelations among immune defense indexes reflect major components of the immune system in a free-living vertebrate

Understanding the relationships among immune components in free-living animals is a challenge in ecoimmunology, and it is important not only for selecting the immune assays to be used but also for more knowledgeable interpretation of results. In this study, we investigated the relationships among six immune defense indexes commonly used by ecoimmunologists and measured simultaneously in individual free-living tree swallows. Three main axes of variation in immune function were identified using a principal components analysis, representing variation in T-cell, B-cell, and innate immunity. Measures within each axis tended to be positively correlated among individuals, while measures in different axes were uncorrelated. A trade-off between T-cell function and B-cell function became apparent only when variation among individuals in body condition, age, and general quality was taken into account. Interestingly, the level of natural antibodies, a component of innate immunity, showed the strongest association with components of acquired B-cell function, possibly reflecting a common underlying genetic mechanism, as has been documented in poultry. Our results indicate that despite the complexity of the immune system, important insights can be gained by using the currently available assays but in a more comprehensive approach than has generally been used in the field of ecoimmunology.     

Degradation phase of apoptosis during the early stages of human metanephros development

Apoptosis as a vital process is necessary for human intrauterine development. Not only the induction and course of apoptosis, but engulfment of the apoptotic cells (bodies) were the centre of our interest. Macrophages were detected in the early stages of human intrauterine development and the role of macrophages in the clearance of apoptotic cells in the early stages of human metanephros development was confirmed.     

Cadherin-catenin proteins in vertebrate development

Cadherin-catenin adhesion is pivotal for the development of multicellular organisms. Features such as a large repertoire of homotypically interacting cadherins, rapid assembly and disassembly, and a connection to a force-generating actin cytoskeleton make cadherin-mediated junctions ideal structures for the execution of complex changes in cell and tissue morphology during development. Recent findings highlight the role of cadherin-catenin proteins as critical regulators of major developmental pathways. We re-evaluate the significance of cadherin-catenin adhesion structures and propose that in addition to intercellular adhesion, they may be used as biosensors of the external cellular environment that help adjust the behavior of individual cells to ensure survival of the entire organism.     

Changes in the protein spectrum of the chick embryo mesonephros and metanephros in the course of development

The protein spectra of two fractions (the soluble and the membrane fraction) of chick embryo kidney homogenates were isolated by electrophoresis on polyacrylamide gels with the aim of detecting the kidney differentiation process at the molecular level and, at the same time, of evaluating similarities in the construction of the mesonephros and metanephros at this level. Corresponding stages of the above two types of kidney were chosen for studying changes in protein structure during differentiation--i.e. the outset of differentiation (the 6-day mesonephros, the 11-day metanephros) and the stage of full maturity (the 14-day mesonephros, the 20-day metanephros). A total of 36 proteins was distinguished. The analysis of the protein spectra showed that the number of proteins changes but slightly during differentiation; the protein composition of the two types of kidney during differentiation altered by 20-35% of the total number of proteins; the similarity of the protein composition of the corresponding stages of mesonephros and metanephros, expressed as the proportion of the number of identical proteins, was greater than the mutual similarity of different developmental stages of the same type of kidney. The percentage of different proteins at corresponding stages of the kidneys varied from 5% to 23% of the total number of proteins detected.     

Glycine-receptors in the vertebrate central nervous system

Evidence for the existence of glycine-receptors in the vertebrate central nervous system (CNS) has been reviewed and analyzed. Biochemical studies have supported iontophoretic findings that such receptors exist in several regions of the CNS. Subcellular studies on the displacement of 3H-strychnine binding by glycine and on the effects of strychnine on 3H-glycine binding have revealed that strychnine does not interact directly with glycine-receptors, lending support to studies performed in situ. Approaches toward glycine-receptors remain limited due to the inavailability of a specific glycine-antagonist.