Nobelpreisträgerin für Medizin 1995

Christiane Volhard wurde während des Zweiten Weltkriegs am 20. Oktober 1942 in Magdeburg als zweites von fünf Kindern geboren. Ihr Vater, Rolf Volhard, war Architekt, ihre Mutter sozial und kulturell engagiert und begabt.

Ihre Jugend verbrachte sie nahe Frankfurt in einer Wohnung mit Garten und einem nahegelegenen Wald. Ihre Eltern waren talentierte Musiker und malten, was die Kinder natürlich stark beeinflusste und bereicherte. Christiane lernte Flöte spielen, doch ihre Geschwister hatten mehr Talent als sie.

Während der schweren Nachkriegszeit hatten die Volhards wenig Mittel, und so nähten sie ihre Kleider oft selbst. Generell machten sie alles, was möglich war selbst, liessen es sich durch Bekannte machen und kauften wenig ein.

Eine Schwester und ein Bruder von Christiane wurden Architekten, eine Schwester studierte Musik und die jüngste Schwester wurde Kunstlehrerin. Mit ihren Geschwistern hatte Christiane stets ein gutes Verhältnis.

Schon früh begann sich Christiane für Pflanzen und Tiere zu interessieren und bereits mit 12 Jahren wusste sie, dass sie Biologin werden wollte. Sie liebte ihren Garten, hielt sich Haustiere, hatte jedoch niemanden, der ihr die Naturdinge erklärte. So erwarb sie sich bereits früh schon Wissen aus Büchern. In ihrer Familie war sie die einzige, welche sich zu den Wissenschaften hingezogen fühlte.

Die Schulzeit erlebte Christiane bereichernd und wertvoll, auch wenn sie kaum Hausarbeiten erledigte und recht faul war. So schloss sie denn auch mit einem mässig erfolgreichen Abitur ihre Schulzeit ab.

In der Mittelschule besprachen sie in Biologie moderne Themen wie Genetik, Evolution, Verhaltensforschung. Bei der Abiturfeier referierte Christiane über die "Sprache bei Tieren", inspiriert von Konrad Lorenz und anderen deutschen Forschern.

Am Tag ihres Abitur-Examens, am 26. Februar 1962 starb unvorgesehen ihr Vater.

Ab 1962 begann Christiane in Frankfurt/Main Biologie, Chemie und Physik zu studieren. Später wechselte sie dann zum Biochemiestudium nach Tübingen. Ihr Diplom in Biochemie erlangte sie in Tübingen (1968), die Promotion erfolgte an der Universität Tübingen (1973). Darauf folge ein Postdoc in Basel und Freiburg, eine Aufgabe als Groupleader am EMBL (1978-1981), weiter Nachwuchsgruppenleiter am Friedrich-Miescher-Laboratorium der MPG in Tübingen (1981-1984), und schliesslich Direktorin und Wissenschaftliches Mitglied am Max-Planck-Institut für Entwicklungsbiologie, wo Christiane Nüsslein-Volhard seit 1985 tätig ist.

Zusammen mit ihren amerikanischen Kollegen Eduard B. Lewis und Eric Wieschaus erhält sie 1995 den Nobelpreis für Medizin.

Die Forschungsarbeiten von Christiane Nüsslein-Volhard

Einen grossen Teil ihrer nobelpreisgekrönten Arbeit leistete Frau Nüsslein-Volhard am EMBL, gemeinsam mit ihrem Nobelkollegen Eric Wieschaus. Sie untersuchten die Entwicklung eines befruchteten Eis der Taufliege (Drosophila). Das sind jene kleinen Fliegen, die oft auf überreifem Obst zu finden sind. Weil sie sich sehr leicht züchten lassen und daher oft für Untersuchungen benutzt wurden, gelten sie als "Haustier der Genetiker". So ist auch ihr Erbgut besonders gut untersucht.

Vor allem interessierten sich Nüsslein-Volhard und Wieschaus für Taufliegen-Mutanten. Sie veränderten das Erbgut mit Hilfe chemischer Substanzen, prüften die Auswirkungen, untersuchten, welches Gen verändert war und konnten so dessen Funktion ermitteln.

Während ihrer Drosophila-Forschung erzeugte ihr Forschungsteam mehr als 20.000 unterschiedliche Mutationen und entdeckten die Funktion von rund 120 Genen. Dabei entstand so manches winzige Monster: Fliegen, denen statt der Fühler Beine aus dem Kopf wuchsen, Tiere mit überlangem Rumpf, zu vielen oder fehlenden Flügeln oder Beinen. Weiterhin konnten die beiden Forscher zeigen, dass nur vier Gene innerhalb des Eis die weitere Entwicklung vorprogrammieren. Man nennt diese strukturbestimmenden Gene Morphogene.

Mittlerweile hat sich Christiane Nüsslein-Volhard ein neues Forschungsobjekt ausgesucht, den Zebrafisch, Freilich sind die Entwicklungsvorgänge bei diesem Wirbeltier noch um einiges komplizierter als beim Insekt Taufliege. Zwar steuern die meisten der von ihr in der Taufliege entdeckten Gene auch wichtige Vorgänge bei anderen Tieren und beim Menschen. Und ähnliche Gene sind als "Onkogene" an der Krebsentstehung beteiligt. Aber die Abläufe sind doch beim Fisch und erst recht beim Menschen um vieles verwickelter. Daher ist sie auch skeptisch, wenn über Anwendungen ihrer Forschungen spekuliert wird, etwa zur Heilung von Krebs oder gar zur Korrektur von Erbkrankheiten eines werdenden Kindes durch Eingriff ins Erbgut der Eizelle. Sie betrachtet ihre Arbeit als reine Grundlagenforschung, als Enträtselung des uralten, immer noch wundervollen Vorgangs - dem Werden eines neuen Lebewesens.

Wissenschaftliche Preise / Ehrungen / Mitgliedschaften (Auswahl)

Albert Lasker Medical Research Award (1991)
Nobelpreis für Medizin (1995)
Pour le mérite (1997)
Mitglied der Royal Society London (1990)
Mitglied der National Academy of Sciences Washington (1990)
Mitglied der Leopoldina (1991)

Aktuelle Veröffentlichungen (Auswahl)

St. Johnston, D., C. Nüsslein-Volhard: The Origin of Pattern and Polarity in the Drosophila Embryo. Cell 68, 201-219 (1992).
Ferrandon, D., L. Elphick, C. Nüsslein-Volhard, D. St.Johnston: Staufen protein associates with the 3«UTR of bicoid mRNA to form particles which move in a microtubule-dependent manner. Cell 79, 1221-1232 (1994).
Nüsslein-Volhard, C.: The identification of Genes controlling Development in Flies and Fishes. Les Prix Nobel, Stockholm. Reprinted in: Angew. Chem. Int. Ed. Engl 35, 2176-2187 (1996).
Haffter, P., M. Granato, M. Brand, M.C. Mullins, M. Hammerschmidt, D.A. Kane, J. Odenthal, F.J.M. van Eeden, Y.-J. Jiang, C.-P. Heisenberg, R.N. Kelsh, M. Furutani-Seiki, E. Vogelsang, D. Beuchle, U. Schach, C. Fabian, C. Nüsslein-Volhard: The identification of genes with unique and essential functions in the development of the zebrafish Danio rerio. Development 123, 1-36 (1996).

Auszug aus einer englisch verfassten Autobiografischen Skizze von Ch. N.

...

Initially I was disappointed by the university and missed school, and my friends at school. I also was rather shy and found it quite difficult to design my curriculum on my own and get to know fellow students. The courses in biology in Frankfurt University were quite dull at the time, it seemed that I knew the more exciting things already, and what was new was boring, although there was one course in botany which I enjoyed. Soon I discovered physics, by an excellent series of lectures by Martienssen, a professor of experimental physics in Frankfurt. I also did courses in mathematics and theoretical mechanics which fascinated me for a year, until I found these topics too difficult. Via the class in chemistry I got reminded of my true interests in biology. At that time (Summer 1964) a new curriculum for biochemistry, the only one of its kind in Germany, was started in Tübingen, and I made up my mind quickly, and went there to study biochemistry, leaving family and friends behind. Being a student in Tübingen, a very lovely old town, was fun. I lived close to the market place, right across from the best movie theater. Rather primitive, but pretty, no shower, cold water, no central heating, but everybody I knew lived like that and it was quite romantic. My friends were largely language students, studying Latin, and Rumanian, and English language. I did not like the biochemistry curriculum very much, too much organic chemistry, too little biology. But on the whole it was a good thing to do, because it provided a very solid training in many basic courses, such as physical chemistry with thermodynamics, and stereochemistry, which I liked. In the final year two new professors taught microbiology and genetics, which I liked very much, and I also had a chance to attend seminars and lectures from scientists of the Max-Planck-Institut für Virusforschung, Gerhard Schramm, Alfred Gierer, Friedrich Bonhoeffer, Heinz Schaller, and others. They were teaching very modern things such as protein biosynthesis and DNA replication. This excited me much although I hardly understood the lectures at the time. I did my exams for the Diploma in biochemistry in 1969, as usual for me, with rather mediocre grades because I had not always paid attention, and often had lost interest.

From Heinz Schaller with whom I did my Diploma work I got my first real training in a laboratory. I was his first graduate student and very keen. Heinz is a chemist, and taught me to think in quantitative terms, yields, completeness of reactions, he is an excellent experimenter. My first thesis project on the comparison of DNA sequences of small phages by RNA-DNA hybridisation was given up, after the realization that it would involve predominantly the refinement of techniques, with uncertain success. I finally developed a new method for large scale purification of very clean RNA polymerase, and, in collaboration with another graduate student and friend, Bertold Heyden, isolated RNA polymerase binding sites from fd Phage in order to understand the structure of a promoter. We determined the composition of the strongest binding site and found it to be rather different from that of other sites such as the strongest of ØX 174 and the second strongest from fd. At the time DNA sequencing was not easily possible, so we characterized the sequences by their oligopyrimidine pattern, for which we had developed a new and simple method. It was a quite interesting story which got published as a letter to NATURE.

Although I was an experienced molecular biologist, I got bored with my projects at the end of my thesis (1973). The prospect of continuing the study of transcriptional control via the structure of promoter regions meant developing new methods for DNA sequencing. The field of recombinant DNA technology was growing and a fellow student and good friend, Peter Seeburg, argued strongly for it. I was sceptical, and at that early time, like most other people in Tübingen, did not foresee its powers. At that time, the Max-Planck-Institutes in Tübingen were interesting places. Wolfgang Beermann and Alfred Gierer taught courses in cell and molecular biology. The Friedrich-Miescher-Laboratory was founded, with Friedrich Bonhoeffer, Günther Gerisch and Rolf Knippers as first group leaders. In the laboratory of Alfred Gierer, people were studying regeneration processes in Hydra. Gierer and Hans Meinhardt, a theoretician, developed their gradient model explaining self organisation of polarity from initial fluctuations by lateral inhibition. Although I was far from understanding the model, I realized how interesting the problem of pattern formation was. I looked around and sought advise from two of the hydra people, the American postdocs Hans Bode and Charles David. I also started reading textbooks such as the lectures on developmental biology by Alfred Kühn. Another strong influence came from the work of Friedrich Bonhoeffer in molecular genetics. Friedrich studied DNA replication in E.coli at the time. He performed a genetic screen for mutations affecting replication, using quite sophisticated and elegant methods to make it work with large numbers and high efficiency. His work, which resulted in the identification of the gene encoding the replicating DNA polymerase and a number of other novel genes, convinced me of the powers of genetics in analysing complex processes. I looked around for an organism in which genetics could be applied to developmental problems, and found the descriptions of the early Drosophila mutants, including bicaudal, in a review by Ted Wright (1971). Further, the description of the first rescue experiments of a maternal mutant was published by Garen and Gehring in 1972.

I read and thought and discussed, and finally decided as a postdoctoral project to score for mutations affecting the informational content of the egg cell, with the aim of using them to isolate and identify morphogens in injection assays, in which the rescue of a mutant phenotype was indicative of the presence of an activity lacking in the mutant embryo, possibly the gene product. The only interesting maternal mutant known at that time was bicaudal, which had been discovered by Alice Bull, and described in 1966. Mutant embryos display mirror image duplications of the abdomen, a spectacular and very puzzling phenomenon, which however showed little penetrance. I met Walter Gehring at a meeting in 1973 in Freiburg, and had the courage to ask him about bicaudal, and whether he would let me work in his laboratory in Basel. I went there at the beginning of 1975, supported by a long term EMBO fellowship.

I immediately loved working with flies. They fascinated me, and followed me around in my dreams. Basel and the Biozentrum was a very good place to spend ones postdoctoral times. I met Eric Wieschaus who just had finished his thesis in Walter Gehring's lab. His thesis project on the origin of imaginal disc cells in the blastoderm interested me very much. I learned a great deal about the use of genetics to study development in discussions with Eric. I also learned to have conversations with my fellow postdocs in English, and enjoyed the Swiss language and the lovely old town. It was difficult to be a beginner in everything, after having been an expert in almost everything in the previous lab. Soon after I started as a postdoc, most people in the Gehring lab began to work on recombinant DNA and molecular biology with the aim to clone developmentally interesting genes. Spyros Artavanis, Paul Schedl and David Ish Horowicz were postdocs at the same time. Eric, soon after I came, left for Zurich to do a postdoc in the lab of Rolf Nöthiger, but continued his collaboration with two postdocs in the lab on the transplantation of pole cells in order to investigate the female germline in chimeras. Jeanette Holden, an excellent geneticist who had done her thesis with David Suzuki on dominant temperature sensitive mutations taught me genetics of Drosophila. The problem of studying embryonic mutants at the time was that the methods for collecting eggs and inspecting embryos were both tedious and unsatisfactory. It was hard to see structures, segments, and their polarity in the living embryo, and fixation and clearing methods were not available. With the help and support of Jeanette Holden and David Ish Horowicz, we developed some tricks which proved helpful in scoring mutant embryos from many lines. The most important of them, the block system for egg collection and replica plating in flies is my first Drosophila publication, in Drosophila Information Service, 1977. With Jitse van der Meer, we developed a fixation and clearing technique which enabled the scoring of the larval cuticle in great detail. Using these techniques, I recovered and investigated the original bicaudal mutant. I also did a small screen for maternal mutants which was successful in that it taught me how difficult such a screen was to do on a large scale. In this screen of 100 chromosomes, a maternal mutant which later was found to be immensely interesting, C79, later called dorsal, was isolated. I did a detailed study of bicaudal, the most difficult mutant I ever studied, with unbelievable patience and in retrospect little reward. I published a paper on bicaudal, but I did not easily find a job.

With a fellowship from the DFG I went for a year (1977) to work in Freiburg in the lab of the famous insect embryologist Klaus Sander. Klaus Sander had been the first to describe gradients in the insect egg. He had done elegant experiments in which he translocated a symbiont ball localized to the posterior pole in a leaf hopper embryo and thereby changed the polarity and pattern over large distances of the egg. In Freiburg, with Margit Schardin, we did a fate map for the larval cuticle using laser ablations of Drosophila blastoderm cells. This experiment was important in showing that the primordia of individual segments in the blastoderm stage were no more than three cells wide. It also led to a very detailed examination and description of the segmental pattern of the Drosophila larva which we later used in our screens. I continued the work on dorsal, discovered the recessive phenotype and interpreted the phenotype postulating a gradient determining the dorsoventral axis. At that time, gradients were not widely accepted as mechanisms, in particular biochemists were highly sceptical, however the Tübingen influence made such models attractive to me. I presented this and the bicaudal work at the annual symposium of the American Society of Developmental Biology in Madison in 1978, my first trip to the US. Pedro Santamaria, a postdoc with whom I shared the lab in Freiburg, was a skillful transplantation person, he did some attempts to rescue the dorsal phenotype by transplantation of wildtype cytoplasm. We could not see much of an effect, but later in Heidelberg I looked at the preps again with a better microscope and found that there was some rescue! Unfortunately by that time Pedro was back in Paris and I had lots of other things to do - so this story had to wait - it finally got published 5 years later.

Both Eric and I got a job offer from John Kendrew, the director general of the European Molecular Biology Laboratory in Heidelberg, that was newly founded and recruiting in many areas. We both accepted and worked there for three years, 1978-1980. I had applied to the EMBL earlier, but at that time they did not think I could establish a fly group alone. When our joint offer came, we were very pleased, because we could imagine that it would be fun to share a lab, and at least I did not have another option. Eric and I always had kept in touch, while I was in Basel and Freiburg and he in Zurich, and we used to discuss our experiments together. I felt at the time that Eric was much more successful than I, he was extremely productive during his time in Zurich, and worked on many very original projects, germ line, cell lineage, sex determination, where not many people could follow him. I also had the impression that I was dependent on him because he had more fly experience and without him I would not have gotten the job. This made our start in Heidelberg a little difficult, until we sorted things out, and from then on we thoroughly enjoyed working in the same lab. It was tiny - we, although both group leaders, shared a technician, Hildegard Kluding, and a stock keeper who also did cuticle preps for us. Initially we both had our own projects which we tried to pursue independently (while discussing them all the time). Soon we realised that the problems of close proximity and in sharing a technician would be eased if we let Hildegard do projects that interested us both. One of our first joint projects was the analysis of Krüppel, a segmentation mutant which we found published in a textbook by Alfred Kühn. It had originally been described in 1950 by Hans Gloor, who, in Geneva, still kept the stock and sent it to us. We let Hildegard do most of the Krüppel experiments. Our collection of mutants affecting segment number increased, tempting us to do a "shelf" screen. In the cuticle preps of embryos produced by our stock collection (we took from the shelf) we found a number of interesting and novel phenotypes. Gary Struhl, then a graduate student with Peter Lawrence in Cambridge, showed us homozygous Antennapedia, and wingless embryo preparations, which were very exciting. We realized that the screening for embryonic mutants would be very rewarding, and that we were the only people in the world who could do it. In contrast, the screen for maternals, which I was trying to work out at that time, was much more difficult, because it requires an additional generation and selection system. We invented some more tricks such as the little nets to fix and clear embryos from 7 mutants at the same time, and did the first screen, for zygotic mutants on the second chromosome, just Eric and I, supported by Hildegard and a second technician. The screen of 4200 second chromosomes took no more than three months (autumn 1979). It was extremely exciting - no major disasters, hard work, and great fun. Early on it was already evident that the screen was a success, and early on we realized the pair rule, the strange skipping of portions from every other segment ("2-4-6-8-type"). We had seen the mirror images displayed by the segment polarity mutants ("gooseberry type") before, also the "notch type" - the neuralized mutants. As a side project we grew up the homozygous flies from the 1000 or so non lethal lines and tested their fertility, and the fertility of their daughters (to screen for grandchildless mutants). We recovered torso, gurken and tudor, three very valuable maternal mutants in this screen. We also, by chance, found the first Toll, BicD and easter allele. At the end of the screen Gary Struhl, and somewhat later Gerd Jürgens joined us, very stimulating, critical and knowledgeable discussants. We sorted things out, owing to the very competent help of Hildegard and the stock keepers, in a very short time, and decided, after some debates whether to wait until the screens of the other two chromosomes had been done as well, to try to publish the essential conclusions on the segmentation genes in an article in Nature. Although there were not many people working close enough to be competing with us, people started to get interested in this type of mutants, and although we certainly had the most complete collection, reports on individual mutants where probably able to spoil much of the fun for us. The paper was published in October 1980, with a very pretty cover picture, in NATURE.

We continued with the screens of the two other chromosomes, with Gerd Jürgens who, as a very skillful and experienced geneticist, organized the third chromosomal screen. We even got a little bit more space and an extra "Denkzimmer" (office space), but on the whole the EMBL of that time, with its strong emphasis on expensive high tech experimental set ups, was not the best place for us, and sometimes it struck us how strange it was to discover very exciting things and know at the same time that there was not a single person in the entire institute outside of our lab who would appreciate it. There was one other laboratory working with Drosophila, they tried to develop cloning techniques and finally cloned an eye colour gene, white. Admittedly, we also did not have great interest in what other people were doing at the EMBL, it was so far from our work and we had so little time, but we enjoyed the international atmosphere and were good citizens of the place. We had very good working conditions, as people at the EMBL had them, and we used our great chance - we could not have been more successful - but the people who had given us this chance were unable to realize this. Eric even before finishing the first screen started to apply for jobs in the US, and got an offer in Princeton for work he had done before the screen. I got an extension to my contract for another three years, but felt uncomfortable to stay at the EMBL without Eric. Luckily I got an offer for a junior position at the Friedrich-Miescher-Laboratory of the Max-Planck-Society in Tübingen and moved there in spring 1981.

The FML consists of four groups, the groupleaders stay for not longer than six years, and are entirely free in their research topics. They have a generous budget, enough space and no teaching obligations. Great conditions and a great challenge. At the time I was there, I much enjoyed the interactions with the groups of Rolf Kemler and Walter Birchmeier, and, in the last year, Peter Ekblom. I was lucky because Gerd Jürgens came along and soon we were joined by Kathryn Anderson as a postdoc. Kathryn wanted to work on dorsal and pursue the rescue experiments. Both Gerd and Kathryn are excellent geneticists with whom it was an intellectual challenge and pleasure to collaborate. In 1982 we did the large scale screen for maternal mutants on the third chromosome in which many of the genes involved in axis determination, including bicoid, and oskar and most of the dorsal-group genes were identified. Gerd, whose interest was to look for maternal homeotic mutations, prepared the screen that involved an elegant crossing scheme proposed by Gary Struhl. As students, Hans Georg Frohnhöfer and Ruth Lehmann started during the first year. Hans Georg initially did pole cell transplantations to investigate the maternal contribution of several zygotic mutants, he later worked on bicoid. Ruth had worked with Campos Ortega before on the neurogenic genes, she already had much knowledge on fly embryology. All were very enthusiastic and made a great team. However, the technicians in Tübingen enjoyed the fly work decidedly less than those in Heidelberg, and we had some difficult times getting food and keeping the stocks, owing to that. But soon we got efficient help from undergraduate students, some of whom came to us via lab courses we taught during the university vacations.

The maternal screen was much harder than the screens we had done before. It was also a difficult task to divide up the work between the people, as the importance of the individual mutants only became clear following rather detailed studies. The obvious groups of phenotypes were readily analyzed, what was more difficult was to take care of all the other mutants (more than 300 total) we had collected. After several attempts to sort those out, we decided to concentrate on the maternal mutants involved in axis determination, and not complete the genetical and phenotypical characterisation of the entire collection. Gerd and I still had to finish some of the projects on segmentation mutants, including the papers on the zygotic screens done in Heidelberg, which finally got published in three papers in Roux archives in 1984.

For the phenotypical and genetical analysis, the maternal mutants, soon including the ones on the second chromosome Trudi Schüpbach and Eric Wieschaus had isolated, were divided into phenotypic groups, which roughly corresponded to the four systems of axis determination defined later. Kathryn Anderson, later Siegfried Roth and Dave Stein, studied the dorsal group genes including cactus, Ruth Lehmann concentrated on the posterior group, and Hans Georg Frohnhöfer on the anterior mutants. Initially he also worked on the genes torso and torsolike, which he recognized as acting independently of the anterior group of genes. Martin Klingler concentrated, later, on this terminal group. An important method to analyse the function of the genes we used in my laboratory was cytoplasmic transplantation. These experiments were very successful. Kathryn Anderson showed that among the dorsal-group genes in many cases the RNA was the rescuing principle. Hans Georg and Ruth discovered localisation of activities with long range effects at the anterior and posterior pole of the egg. These studies were started with the mutants bicoid and oskar, but also extended to wildtype embryos. A first model describing the three independent systems involved in establishing the anteroposterior axis was presented in an article in SCIENCE, with Frohnhöfer and Lehmann, in 1987. At the time the first Drosophila segmentation genes had been cloned and found to encode transcription factors. The first gap gene, Krüppel, was cloned in the group of Herbert Jäckle, who had a small independent research group in the neighboring Max-Planck-Institut für Entwicklungsbiologie (formerly Virusforschung, the institute in which I had done my PhD). In my lab, molecular analysis was begun rather late, as we felt it important to investigate the properties of the individual genes as carefully as possible before embarking in tedious molecular cloning, that was not easy at the time.

In the meantime, I was appointed as director of an independent division at the Max-Planck-Institut für Entwicklungsbiologie, the position I am still holding. We moved across the yard in 1986. The institute has four more directors, working on cell biology, with frog (Peter Hausen) and neuroembryology, with chick embryos (Alfred Gierer, Friedrich Bonhoeffer and Uli Schwarz). My group got larger, and we started doing molecular work, with the analysis of the localization of the RNA of bicoid (cloned in the lab of Marcus Noll in Basel). Wolfgang Driever as a graduate student made an antibody against the bicoid protein and discovered the bicoid protein gradient that determines, in a concentration dependent manner, the expression pattern of other segmentation genes. Wolfgang established many molecular methods in my lab, and subsequently Frank Sprenger and Leslie Stevens cloned torso, followed by Daniel St Johnston with the cloning of staufen, and Robert Geisler's cloning of cactus. The improvements in the techniques of visualisation of the gene products by in situ hybridisation and antibody stainings complemented the transplantation studies done earlier, resulting in several exciting discoveries concerning the establishment of gradients in the extracellular space and by nuclear localisation by Dave Stein and Siegfried Roth. These investigations gradually lead to a more comprehensive understanding of the principles of axis determination in the embryo, presented first in a review in DEVELOPMENT in 1990.

Already in 1984 or so - I got excited about the 1982 paper of George Streisinger on Zebrafish, and at the side explored whether zebrafish could eventually be established as a system for the genetic analysis of vertebrate development. The basis for this interest was the problem of generalisation, the question to what extent our results could be applied to an understanding of vertebrates including man. These early intentions to investigate zebrafish were retarded significantly by the subsequent demanding molecular studies on Drosophila, with the success that I had not expected when, as early as 1986, I brought the first fish tanks into the lab. Two graduate students, Stefan Schulte-Merker, who started in 1988 and Matthias Hammerschmidt, were the first fish people in the lab, and Nancy Hopkins from MIT spent a sabbatical year with our fish and us. They and others who joined later were very helpful in developing the tools for breeding and keeping many stocks of fish with safety and efficiency. These efforts resulted in the building of a fish house, with 7000 aquaria of our design, inaugurated in September 1992. Almost to the day three years later we submitted for publication the manuscripts describing 1200 zebrafish mutants, which a group of twelve scientists, with a number of technicians and students, had isolated in a large scale screen.

In my lab, we will continue working on the investigation of the molecular mechanisms involved in the establishment of polarity in the Drosophila embryo, as well as continue the exploration of the zebrafish as a model for the study of vertebrate specific features. We believe that the combination of several approaches and systems in one laboratory provides a powerful basis for further understanding of the development of complexity in the life of an animal.