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Models in developmental biology continue to yield valuable insights, yet do not play a strong role as guides to experiment. This may be because of the largely unexplored complexity of most developing organisms, and the fact that the most powerful models work at a very abstract level. In Dictyostelium discoideum, however, a fully formed model incorporating detailed experimental results is now available.
The early studies of evolutionary developmental biology (Evo-Devo) come from several sources. Tributaries flowing into Evo-Devo came from such disciplines as embryology, developmental genetics, evolutionary biology, ecology, paleontology, systematics, medical embryology and mathematical modeling. This essay will trace one of the major pathways, that from evolutionary embryology to Evo-Devo and it will show the interactions of this pathway with two other sources of Evo-Devo: ecological developmental biology and medical developmental biology. Together, these three fields are forming a more inclusive evolutionary developmental biology that is revitalizing and providing answers to old and important questions involving the formation of biodiversity on Earth. The phenotype of Evo-Devo is limited by internal constraints on what could be known given the methods and equipment of the time and it has been framed by external factors that include both academic and global politics.
A striking finding of the human and mouse genome sequencing projects is that, although there are many differences between the two species, they have similar numbers of genes. The differences arise during development and are driven, in part, by changes in gene expression. The MRC-Wellcome Trust Human Developmental Biology Resource (HDBR) is a unique resource that provides human embryonic and foetal tissues to the scientific community, enabling gene-expression studies at these crucial periods of development.
The study of developmental biology has benefited greatly from the insights gained using amphibians as experimental models. Although Xenopus is currently the predominant model, much of our embryological knowledge derives from research on other amphibians. I will review some of these discoveries, made through astute choice of model organism, and I will examine the reasons behind the adoption of Xenopus as the standard for amphibian research. Additionally, I will discuss the diversity in developmental and reproductive strategies that exists within the Amphibia, and consider some of the recent advances in our understanding of the mechanisms underlying this developmental diversity.
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Developmental biology has been taught at the Pontificia Universidad Católica del Ecuador, in Quito for 30 years by the author. The experience of teaching development is described within the broader context of science in Latin America. It is recognized that developmental biology is poorly represented in research and teaching in this part of the world. The teaching of developmental biology to Ecuadorian students contributes to their intellectual training, by helping them to integrate concepts derived from various branches of biology. Moreover, the highly conserved molecular mechanisms of development provide extraordinary examples of the unity of biology, and many complex biological processes can be more easily grasped when studying embryos.
The field of developmental biology has a history that spans the last 500 years. Within the last 10 years, our understanding of developmental mechanisms has grown exponentially by employing modern techniques of genetics and molecular biology, frequently combined with experimental embryology and the use of molecular markers, rather than solely morphology, to identify critical populations of cells and their state of differentiation. Three main principles have emerged. First, mechanisms of development are highly conserved, both among developing rudiments of a variety of organ systems and among diverse organisms. This conservation occurs both at the level of tissue and cellular mechanisms, and at the molecular level. Second, the development of organ rudiments is influenced by surrounding tissues through interactions called inductive interactions. Such interactions are mediated by highly conserved growth factors and signaling systems. Third, development is a life-long process and can be reawakened in events such as wound healing and regeneration, and in certain diseases. Advances in understanding normal development provide hope that diseases in which development runs amuck, such as cancer, may soon be preventable and fully treatable. Supported by NS 18112 and DC 04185 from the NIH.
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The 2004 Santa Cruz Developmental Biology Meeting took place August 5th-8th and covered a diverse range of current topics in developmental biology. This report discusses some of the highlights.
The present paper analyzes the use and understanding of the homology concept across different biological disciplines. It is argued that in its history, the homology concept underwent a sort of adaptive radiation. Once it migrated from comparative anatomy into new biological fields, the homology concept changed in accordance with the theoretical aims and interests of these disciplines. The paper gives a case study of the theoretical role that homology plays in comparative and evolutionary biology, in molecular biology, and in evolutionary developmental biology. It is shown that the concept or variant of homology preferred by a particular biological field is used to bring about items of biological knowledge that are characteristic for this field. A particular branch of biology uses its homology concept to pursue its specific theoretical goals.
In recent years developmental biology has contributed a great deal to cancer research. This is in part because both fields address the question of how genes control the three-dimensional organisation of tissues, and how mutation of genes alters this. But also in recent years, the discovery that signalling pathways are conserved from worms to man, combined with the power of developmental biology's model organisms, principally Drosophila and C. elegans, to reveal signalling pathways that control tissue growth and organisation, has had a huge impact. Examples of this are the subject of the reviews in this issue, including the EGF-receptor, Wnt/APC/catenin, TGF-beta/Smad and hedgehog/patched/smoothened pathways, all of which were discovered and/or pieced together in model organisms, and all of which are disrupted by mutation in human cancer. Other topics considered are the control and execution of apoptosis; the search for tumour-suppressor-like genes in Drosophila; and genes of the Polycomb and Trithorax Groups that regulate the commitment of cells to patterns of differentiation, and that are among the targets for chromosome translocations. These stories illustrate how developmental biology has shown that there are many more signalling pathways relevant to neoplasia than the receptor tyrosine kinase pathways that first dominated the field; and that the signalling is more than just mitogenic or anti-mitogenic, and should be viewed as providing cells with information about their position and neighbours, that determines their role, differentiation and behaviour.
Models have been particularly useful in developmental biology over the last 30 years. At first, underlying control mechanisms were poorly understood, but over time a wealth of detailed information became available to provide an increasingly detailed knowledge of underlying mechanisms, at levels from genes through cells to organs, organisms and populations. Models are also of great value in teaching developmental biology, as they allow students to explore phenomena hard to perceive directly because of their scale, accessibility, expense or other considerations. A model may allow students to "experiment" in ways which would be impractical in real life, as well as give them a deep understanding of competing hypotheses of development. Lastly, students can be challenged to produce models of their own, whereas only rarely are they able to carry out original experiments. I discuss two main kinds of models and their uses in generating, testing and expounding hypotheses and point out dangers in the use of models in education. Models may draw upon and reflect the consensus paradigm in the field: a researcher may be able to appreciate that models are interim conditional statements of probability and use them to generate new knowledge. A student may be less able to do so and may fail to appreciate where new knowledge will come from. And unlike physics, biology is stochastic and contingent and can never be entirely deduced from first principles, implying that models can never be as perfect in any biological field as they can be in some other fields.
The Finnish school of developmental biology can be considered a direct descendant of Spemann's school as both the original technology and the fundamental problems were introduced into Finland by Gunnar Ekman (1883-1937) who had worked for extended periods in Germany. After his early death, the work was continued by Sulo Toivonen (1909-1995), and until 1968 the group explored the mechanisms of primary induction and the subsequent segregation of the central nervous system. The extensive investigations led to the formulation of the "double-gradient" hypothesis and ultimately to its experimental vindication.
The emerging field of evolutionary developmental biology (evo-devo) continues to operate largely under a single paradigm. In this paradigm developmental regulatory genes and processes are compared among a collection of "model organisms" selected primarily on the basis of their historical utility in the study of development. This approach has proven to be extremely informative, revealing an unexpected deep evolutionary conservation among developmental genes and genetic systems. Despite its success, concern has been expressed regarding its limitations. We discuss the "model organism" paradigm in evo-devo research. Based on our interpretation of its limitations, we propose a separate but complementary approach that is centered on "model groups." These groups are selected on the basis of their taxonomic affinity and their relevance to questions of interest to evo-devo biologists. We further discuss the Tetraodontiformes (Teleostei, Pisces) as an example of a "model group" for the evo-devo study of vertebrate skeletal elements.
Cell and developmental biology are distinct disciplines with clear differences in emphasis and domains of interest, yet they also share a common historic origin and benefit from an increasingly productive exchange of insights and influences. Our goal in this commentary is to examine the common origin of cell and developmental biology, to explore ways in which they currently interact, and to consider the connections and differences that exist between these two fields.
This report describes the road map we followed at our university to accommodate three main factors: financial pressure within the university system; desire to enhance the learning experience of undergraduates; and motivation to increase the prominence of the discipline of developmental biology in our university. We engineered a novel, multi-year undergraduate developmental biology program which was "student-oriented," ensuring that students were continually exposed to the underlying principles and philosophy of this discipline throughout their undergraduate career. Among its key features are introductory lectures in core courses in the first year, which emphasize the relevance of developmental biology to tissue engineering, reproductive medicine, therapeutic approaches in medicine, agriculture and aquaculture. State-of-the-art animated computer graphics and images of high visual impact are also used. In addition, students are streamed into the developmental biology track in the second year, using courses like human embryology and courses shared with cell biology, which include practicals based on modern experimental approaches. Finally, fully dedicated third-year courses in developmental biology are undertaken in conjunction with stand-alone practical courses where students experiencefirst-hand work in a research laboratory. Our philosophy is a "cradle-to-grave" approach to the education of undergraduates so as to prepare highly motivated, enthusiastic and well-educated developmental biologists for entry into graduate programs and ultimately post-doctoral research.