Preface

In recent years, the British Society for Cell Biology (BSCB) and the British Society for Developmental Biology (BSDB), have held their Annual Meetings conjointly, an arrangement that has brought many benefits in terms of increased numbers of participants and shared interests. Topics each year have been selected independently by the two societies and have not in general been coordinated, although there is enough common ground to make most talks accessible to all. In the 1991 Annual Meeting, however, the societies moved a step closer by choosing the same topic for the two main symposia - the proceedings of which are customarily published as Supplements to Development and The Journal of Cell Science. In conjunction with a third scientific society - the Brain Research Association (BRA) - it was decided to focus on the development of the nervous system, with special emphasis on its cellular basis.

Neurobiology is inherently multidisciplinary, with significant applications to everything from philosophy to physics. It is an enormous area of research (the number of practising neurobiologists world-wide far exceeds that of cell biologists and developmental biologists combined) and many members of BSDB and BSCB, and of course BRA, have a professional interest in the nervous system. It seemed a valuable endeavour to try to bring these research workers together and to bridge arbitrary divisions between subject matter and allow common elements to emerge. The programme of invited talks thus addressed everything from the molecular basis of neuronal differentiation at the single cell level, to the coordinated changes in large numbers of cells within an embryo, and to the structure and function of mammalian brain.

The study of nervous system development has, since its inception a century ago, had as its proper concern the study of nerve cells. The formation of nerve tracts and peripheral nerves, the establishment of synaptic projections and even the embryonic development of major aspects of gross anatomy, all have their origin in the behaviour, form and biochemical identity of individual nerve cells. This cellular aspect has in the past been most dramatically emphasized in studies of invertebrate nervous systems, in which the same nerve cell can often be identified from animal to animal and its form and behaviour monitored over the course of development. This area of current research was represented during the meeting by talks on the development of segmental identity in the leech and the early decisions in Drosophila neurogenesis.

An even greater emphasis at this meeting, reflected in the selection of papers published in the Supplement to Development, was placed on the analysis of vertebrate nervous systems and mammalian brain at the single cell level. Pioneering work on the development of zebrafish spinal cord allows, as in selected invertebrate systems, the form and fate of single identified cells to be followed with development. Other regions of the vertebrate nervous system are also yielding valuable insights at the cellular level. Patterns of gene expression and production of growth and survival factors control cell diversity in the vertebrate brain as elsewhere in the nervous system. The lineage of cells has been monitored during chick hindbrain development and in rat cerebral cortex. Multiple factors control cell fate and diversity in the vertebrate nervous system, and many of these have been isolated and their mode of action analysed.

Cell biologists - on the other hand - begin with an interest in individual cells and seek to learn how the molecules they contain and interact with, define their form and behaviour. And yet, as is apparent in the collection of articles published in the Supplement to the Journal of Cell Science, when the subject is nerve cells, then cellular properties have major implications for the entire multicellular tissue. Properties such as the differentiation of nerve cell precursors into a myriad of subtypes, responses to extracellular matrix molecules, selective migration and intercellular signalling are common to all living cells. But they find their highest and most complex expression in the cells that make up the nervous system.

Some of the most striking reports during the meeting concerned the properties of single cells, individually isolated in tissue culture. Studies of the migration of growth cones over different surfaces, their collapse in contact with non-permissive cells, the selective formation of dendrites and axons, the establishment of synapses, and the modulation of these with electrical activity - all have been studied with single cells in vitro. In every case, attempts have been made to analyse these properties at the molecular level. Thus the differentiation of axons and dendrites is seen to be associated with, and perhaps caused by, changes in microtubule-associated proteins, whereas the guidance of growth cones and the formation of synapses are both inextricably linked to the cascades of cell signalling molecules.

One of the successes of this novel meeting was the emergence of underlying themes and approaches common to both developmental and cell biology. The second coming of the light microscope, armed with computer analysis and fluorescent probes, is revealed in every aspect of present-day neurobiology. Light microscopes are today used to track individual cells through the nervous system, to locate specific molecules within cells, to monitor minute changes in the morphology of growth cones and synapses. A second leitmotif of the meeting was the application of recombinant DNA technology and the new genetics to neurobiological questions. We heard of master genes that control differentiation and development in both invertebrate and vertebrate nervous systems, of genetic manipulations used to dissect development and to monitor lineages, and how at the molecular level, recombinant DNA technology makes it possible to identify, isolate and probe the function of the molecules responsible for nervous system development.

The papers from this meeting, here published conjointly in Development and Journal of Cell Science Supplements, relate to a host of biological problems, intellectual challenges and techniques. We hope they will attract the interest of developmental biologists and cell biologists with many different backgrounds and foster awareness of the central importance of Developmental Nerve Cell Biology as a discipline in its own right.

Hugh Perry

Andrew Lumsden

Roger Keynes

Nigel Holder

Dennis Bray