Spilling the beans on java 3D: a tool for the virtual anatomist.
The computing world has just provided the anatomist with another tool: Java 3D, within the Java 2 platform. On December 9, 1998, Sun Microsystems released Java 2. Java 3D classes are now included in the jar (Java Archive) archives of the extensions directory of Java 2. Java 3D is also a part of the Java Media Suite of APIs (Application Programming Interfaces). But what is Java? How does Java 3D work? How do you view Java 3D objects? A brief introduction to the concepts of Java and object-oriented programming is provided. Also, there is a short description of the tools of Java 3D and of the Java 3D viewer. Thus, the virtual anatomist has another set of computer tools to use for modeling various aspects of anatomy, such as embryological development. Also, the virtual anatomist will be able to assist the surgeon with virtual surgery using the tools found in Java 3D. Java 3D will be able to fulfill gaps, such as the lack of platform independence, interactivity, and manipulability of 3D images, currently existing in many anatomical computer-aided learning programs. (+info
Zebrafish tbx-c functions during formation of midline structures.
Several genes containing the conserved T-box region in invertebrates and vertebrates have been reported recently. Here, we describe three novel members of the T-box gene family in zebrafish. One of these genes, tbx-c, is studied in detail. It is expressed in the axial mesoderm, notably, in the notochordal precursor cells immediately before formation of the notochord and in the chordoneural hinge of the tail bud, after the notochord is formed. In addition, its expression is detected in the ventral forebrain, sensory neurons, fin buds and excretory system. The expression pattern of tbx-c differs from that of the other two related genes, tbx-a and tbx-b. The developmental role of tbx-c has been analysed by overexpression of the full-length tbx-c mRNA and a truncated form of tbx-c mRNA, which encodes the dominant-negative Tbx-c. Overexpression of tbx-c causes expansion of the midline mesoderm and formation of ectopic midline structures at the expense of lateral mesodermal cells. In dominant-negative experiments, the midline mesoderm is reduced with the expansion of lateral mesoderm to the midline. These results suggest that tbx-c plays a role in formation of the midline mesoderm, particularly, the notochord. Moreover, modulation of tbx-c activity alters the development of primary motor neurons. Results of in vitro analysis in zebrafish animal caps suggest that tbx-c acts downstream of early mesodermal inducers (activin and ntl) and reveal an autoregulatory feedback loop between ntl and tbx-c. These data and analysis of midline (ntl-/- and flh-/-) and lateral mesoderm (spt-/-) mutants suggest that tbx-c may function during formation of the notochord. (+info
Double-stranded RNA injection produces null phenotypes in zebrafish.
Zebrafish is a simple vertebrate that has many attributes that make it ideal for the study of developmental genetics. One feature that has been lacking in this model system is the ability to disable specifically targeted genes. Recently, double-stranded RNA has been used to silence gene expression in the nematode Caenorhabditis elegans. We have found that expression of the green fluorescent protein (GFP) from a microinjected plasmid vector can be suppressed in zebrafish embryos by the coinjection of a double-stranded RNA that is specifically targeted to GFP. To determine that double-stranded RNA can attenuate endogenous gene expression, single-cell zebrafish embryos were injected with double-stranded RNA specifically targeted to Zf-T and Pax6.1. We found that microinjection of double-stranded Zf-T RNA resulted in a high incidence of a phenotype similar to that of ntl. Furthermore, Zf-T gene expression could not be detected by in situ hybridization and the message was decreased by 75% by semiquantitative RT-PCR in 12-h embryos that had been injected with the double-stranded RNA. Expression of the zebrafish genes sonic hedgehog and floating head was altered in the embryos microinjected with the Zf-T double-stranded RNA in a manner that is remarkably similar to the zebrafish no-tail mutant. Microinjection of double-stranded RNA targeted to Pax6.1 was associated with depressed expression of Pax6. 1 and resulted in absent or greatly reduced eye and forebrain development, similar to the phenotype seen in mouse mutants. Simultaneous injection of Pax6.1 and Zf-T resulted in embryos lacking notochords, eyes, and brain structures. (+info
A treasure house of comparative embryology.
The Embryo Collection of the Hubrecht Laboratory is a treasure house of comparative embryology. It is the largest and most important collection of its kind in the world, and consists of thousands of vertebrate embryos stored in alcohol, or prepared as histological sections. Many elusive species are included in the collection, some represented by complete developmental series. The accompanying archives offer a remarkable insight into the methods used to collect embryos form wild animals, as well as the motives behind the founders of the collection. Carefully maintained, documented and catalogued, the collection is available for study by all interested scientists. We argue that this collection is one of the greatest biodiversity resources in existence. (+info
Pieter Nieuwkoop's contributions to the understanding of meso-endoderm induction and neural induction in chordate development.
Pieter Nieuwkoop, who died September 18, 1996, at age 79 in Utrecht, The Netherlands, is remembered by developmental biologists for his numerous research contributions and integrative hypotheses over the past 50 years, especially in the areas of neural induction, meso-endoderm induction, and germ cell induction in chordates. Most of his experimentation was done on the embryos of amphibia, the preferred vertebrate embryo of the early years of the 20th century. One of his last publications contains a comparison of the experimental advantages and disadvantages of anuran and urodele amphibians (Nieuwkoop, 1996). The significance of his findings and interpretations for developmental biology can be estimated from the fact that researchers of many laboratories worldwide continue to work on the phenomena he first described and to extend the hypotheses he first formulated. The aim of this article is to review Nieuwkoop's main contributions and to cite the recent extensions by others. (+info
Embracing complexity: organicism for the 21st century.
Organicism (materialistic holism) has provided the philosophical underpinnings for embryology since the time of Kant. It had influenced the founders of developmental mechanics, and the importance of organicism to embryology was explicitly recognized by such figures as O. Hertwig, H. Spemann, R. Harrison, A. M. Dalq, J. Needham, and C. H. Waddington. Many of the principles of organicism remain in contemporary developmental biology, but they are rarely defined as such. A combination of genetic reductionism and the adoption of holism by unscientific communities has led to the devaluation of organicism as a fruitful heuristic for research. This essay attempts to define organicism, provide a brief history of its importance to experimental embryology, outline some sociologically based reasons for its decline, and document its value in contemporary developmental biology. Based on principles or organicism, developmental biology should become a science of emerging complexity. However, this does mean that some of us will have to learn calculus. (+info
Introducing the Spemann-Mangold organizer: experiments and insights that generated a key concept in developmental biology.
The "organizer paper", published by Hans Spemann and Hilde Mangold in 1924, initiated a new epoch in developmental biology. Also it marked the climax of Spemann's life-long research which began at the end of the nineteenth century. This introduction retraces some of the steps by which Spemann arrived at the organizer concept: The problem of amphibian lens induction including the so-called lens controversy, the early constriction experiments creating double headed malformations, and the homeo- and heteroplastic transplantations during gastrula stages of the newt. Furthermore this paper will--based on historical documents--repudiate some objections raised to the contribution of Spemann and Hilde Mangold to the discovery and interpretation of the organizer effect. (+info
Evolution of the organizer and the chordate body plan.
The discovery of the organizer by Spemann and Mangold in 1924 raised two kinds of questions: those about the means of patterning the chordate body axis and those about the mechanisms of cell determination by induction. Some researchers, stressing the second, have suggested over the years that the organizer is poorly named and doesn't really organize because inducers act permissively, because they are not unique to the organizer, and because multipotent responsive cells develop complex local differentiations under artificial conditions. Furthermore, with the discovery of meso-endoderm induction in 1969, the possibility arose that this earlier induction generates as much organization as, or more than, does the organizer itself. Evidence is summarized in this article that the organizer does fulfill its title with regard to pattern formation: it adds greatly to embryonic organization by providing information about time, place, scale, and orientation for development by nearby members of the large multipotent competence groups surrounding the organizer. Embryos having smaller or larger organizers due to experimental intervention develop defective axial organization. Without an organizer the embryo develops no body axis and none of the four chordate characters: the notochord, gill slits, dorsal hollow nerve chord, and post-anal tail. For normal axis formation, the organizer's tripartite organization is needed. Each part differs in inducers, morphogenesis, and self-differentiation. The organizer is a trait of development of all members of the chordate phylum. In comparison to hemichordates, which constitute a phylum with some similarities to chordates, the chordamesoderm part is unique to the chordate organizer (the trunk-tail organizer). Its convergent extension displaces the gastrula posterior pole from alignment with the animal-vegetal axis and generates a new anteroposterior axis orthogonal to this old one. Once it has extended to full length, its signaling modifies the dorsoventral dimension. This addition to the organizer is seen as a major event in chordate evolution, bringing body organization beyond that achieved by oocyte organization and meso-endoderm induction in other groups. (+info