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Walther Flemming: pioneer of mitosis research
Author: Neidhard Paweletz
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"72 | JANUARY 2001 | VOLUME 2 www.nature.com/reviews/molcellbio PERSPECTIVES by his mentor, Max Schultze, one of the first ?cell biologists?). From Schulze, Flemming learned constructive criticism, the cautious evaluation of results and the avoidance of speculation ? all of which were characteris- tic of his later scientific work. Other features of his research included careful observation, frequent controls and a thorough evaluation of all results. Flemming was also influenced by Rudolf Virchow, one of his academic teachers, and Max Schultze?s students Wilhelm K�hne and Gustav Schwalbe, who implanted in him the idea of the cell as the fundamental, autonomous unit of life. For short periods Flemming assisted in anatomy and histology in W�rzburg and Amsterdam until, in 1870, he was offered the position of Prosektor (leader of dissections and anatomical preparations) in Rostock. He also taught histology and comparative anato- my, and his students were enthusiastic about his talent for drawing, which brought cells, organs or organisms to life on the black- board. Indeed, all of his later publications were illustrated by fine detailed drawings that aided understanding (FIG. 2). At the end of 1870 he presented his Habilitation thesis about connective substances and the vessel wall in molluscs, to become Privatdozent (academic teacher). In February 1872 the head of anatomy at Rostock, Wilhelm Henke, asked Flemming to go with him to the German University of Prague, where Flemming was responsible for all histological lectures, seminars and cours- es. Here, in the same institute as Johannes Evangelista Purkinje, who was considered the father of histology, Flemming began his detailed investigations into cell division. Since the German revolution of 1848, nationalism had been growing all over Europe, and Czech students passionately demanded a Czech University in Prague. So the climate became increasingly hostile until most German professors preferred to return to Germany. Although Flemming was not called to the Chair at K�nigsberg (East famous psychiatrist and neurologist. Flemming grew up in Sachsenberg as a shy but intelligent boy. Although his favourite topics were literature and philology, he decid- ed to study medicine. He began his studies at the University of G�ttingen and continued in T�bingen, Berlin and Rostock. During his training in the clinic at Rostock, Flemming studied histological and zoological prepara- tions under the guidance of Franz Eilhard Schulze (who was himself strongly influenced The German anatomist Walther Flemming began his pioneering studies of mitosis almost 150 years ago. What were his achievements, and where have his discoveries led? Browsing through the latest issues of cell and molecular biology journals, it is striking how many cover pages show images of dividing cells. This reflects the fact that research into cell division is at the forefront of the field. But what are the origins of this discipline? It began in the seventeenth century, when Hooke 1 , van Leeuwenhoek 2 and others discov- ered the cellula as a building block of many organisms. Then, in the first half of the nine- teenth century, Schleiden 3 and Schwann 4 established the ?cell theory?, according to which all organisms are composed of tiny units, the cells. Schleiden and Schwann assumed that cells are formed de novo from an intercellular substance in some kind of crystallization (?free cell formation?) ? an assumption that misled many scientists and inhibited research into cell division for almost three decades. For exam- ple, in 1875 Strasburger 5 published a compre- hensive book Ueber Zellbildung und Zelltheilung (?About cell formation and cell division?) in which he defended free cell for- mation. However, he had abandoned this idea by the time the third edition of his book was published in 1880. By the 1870s, some scientists (such as Dumortier 6 , von Mohl 7 ,Remak 8 and others) had shown that cells multiply by binary fis- sion. At this time, Strasburger?s colleague (and competitor) Walther Flemming (FIG. 1) was beginning detailed studies on dividing cells in different organs and organisms, mainly from the animal kingdom. Flemming?s studies were not hampered by the idea of free cell formation, which he no longer believed in, and they eventually led to a solid foundation for modern cellular and molecular biology. Flemming?s career Walther Flemming was born on 21 April 1843, in Sachsenberg/Mecklenburg in Germany. His father, Carl Friedrich, was a Walther Flemming: pioneer of mitosis research Neidhard Paweletz TIMELINE Figure 1 | Portrait of Walther Flemming. A well- documented appreciation of Flemming?s work is given in The Birth of the Cell by Henry Harris 36 . (Image provided by the Science Photo Library.) Box 1 | Cytoplasm and mitochondria One of Flemming?s favourite topics was the structure and function of the protoplasm. During his careful observations, particularly in the 1880s (REF. 37), he used optimal fixations and different staining procedures to show that the protoplasm has a mainly filamentous appearance; this contradicted the widely accepted proposal by Carl Frommann and Karl Heitzmann of a granular and reticular substructure. Flemming defended his Filartheorie (?theory of a filamentous structure?) vigorously, and surrendered only when he was too ill and weak. In 1898, however, Carl Benda used a special fixation and staining method to show elongated corpuscles in the protoplasm. He termed these mitochondria because of their tendency to form chains. Flemming?s assistant Friedrich Meves 38 later showed, shortly after Flemming?s death, that Flemming was not completely wrong ? Meves identified Flemming?s ?filaments? and Benda?s mitochondria as one and the same. � 2001 Macmillan Magazines Ltd PERSPECTIVES products of cellular metabolism. In addition, he was interested in the involution of adipose tissue, and studied the fine structure of the fibres of connective tissue and their swelling during treatment with acids. At a time when the focus of Flemming?s interest was still the behaviour of individual cells, research into the process of cell division had already begun. In 1873, Schneider 12 sketched the important steps of cell division. He saw the transformation of the nucleus into rod-like structures (St�bchen), which assembled in the centre of the cell (at what we now know as the metaphase plate). At a stage that we now call anaphase, two groups of St�bchen could be seen in the elongated cell. Between 1874 and 1876, Flemming described these steps in more detail 13?15 . Whereas Schneider 12 had postulated that the nucleus undergoes deformation during cell Prussia), as he had hoped, he was recruited to the vacant Chair of Anatomy at Kiel (Schleswig-Holstein). Almost all the medical faculty voted for Flemming. However, during negotiations, one faculty member strongly recommended Friedrich Merkel, an anatomist from Rostock, who was the son- in-law of a well-known German anatomist. Nevertheless, Flemming took up the position in February 1876. Although the Christiana Albertina University in Kiel was very small, the old insti- tute of anatomy was not big enough for the 70 or so medical students. There was not enough money to buy new microscopes and other equipment, and, at the beginning, Flemming took charge of all lectures, seminars and courses without assistance. He had to do bat- tle with the university?s administration; these struggles for resources were a heavy burden for Flemming, a peace-loving man whose stu- dents loved him for his cordiality and benevo- lence. In his late forties, Flemming developed a severe neurological disease from which he did not recover. At the turn of the century, his illness became so severe that he had to retire and, on 4 August 1905, he died aged 62 in Kiel 9 . By this time, however, Flemming?s insti- tute had become a leading centre for research into histology, cytology, comparative anatomy and, in particular, mitosis. Initial studies When Flemming began his research, cell biol- ogy was just beginning to boom (TIMELINE).In 1833, even before Schleiden and Schwann had presented their cell theory 3,4 ,Robert Brown 10 had described an ovoid in the cell as the ?nucleus?, and Dumortier 6 and von Mohl 7 had discovered binary fission of the nucleus and cell. Remak 8 gave the first descriptions of the changes that occur in the nucleus, and Purkinje 11 underlined its importance and the requirement for this organelle throughout the life of a cell. But in 1868, at the beginning of his career, Flemming ? whose knowledge of histology was derived mainly from zoological objects ? was interested in the sensory organs of molluscs. He also studied adipose tissue, and clearly stated its character as con- nective tissue; before this, adipose tissue had been considered to be a separate organ. Flemming also analysed lipid droplets as NATURE REVIEWS | MOLECULAR CELL BIOLOGY VOLUME 2 | JANUARY 2001 | 73 Figure 2 | Illustration from Zellsubstanz, Kern und Zelltheilung 22 . Figure 3 | The progressive and regressive phases of cell division. Mitosis starts with the skein-like form of the nuclear threads (prophase), which changes into the aster (star-like configuration of the threads at prometaphase). This stage moves into the equatorial plate (metaphase), which then immediately forms the double star (anaphase). When the threads have reached the position of the daughter-cell nucleus, the double skein (telophase) can be observed. (Images reproduced from REF. 22). Skein of fine threads (prophase) Spirem Scaffold of the resting nuclei (interphase nuclei) Skein of fine threads (reconstruction phase) Dispirem Two star-like arrangements of the threads (anaphase) Dyaster Condensation on the skein (telophase) Equatorial plate (metaphase) Metakinese Star-like configuration of threads (prometaphase) Aster Scaffold of the resting nucleus (interphase nucleus) Thickenings of the threads and loosening of the skein (late prophase) Progressive phase Mother nucleus Regressive phase Daughter nuclei � 2001 Macmillan Magazines Ltd 74 | JANUARY 2001 | VOLUME 2 www.nature.com/reviews/molcellbio PERSPECTIVES rations ? in particular, the chromatic aber- ration often delivered structures with coloured halos. Moreover, the illumination was not yet very bright and depended strong- ly on the intensity of the daylight. The micro- scopes had no sophisticated condenser sys- tems, so it was not possible to produce a pseudo-phase-contrast image. But Flemming?s drawings clearly showed correct images of the spindle apparatus, for example. In 1891, Flemming published a paper 25 describing the remnants of the spindle just before complete cleavage. He called this the Mittelk�rper or midbody and considered it to be an equivalent of the cell plate in plant cells. Otto B�tschli had shown earlier 26 that a fibrillar structure becomes visible, which he called the pole aster. Edouard van Beneden 27 and, almost simultaneously but independently, Theodor Boveri 28 had found a tiny structure at the pole, which they both termed the Polk�rperchen (polar body), but they had assumed that this formed de novo during cell division. Also in 1891, in a sensational paper 29 , Flemming showed unequivocally that this body is not formed anew but persists, and he coined the term Zentralk�rperchen (central body) or Zentriol (centriole). He was convinced that the filamentous structure of the spin- dle in mitosis was responsible for transport of the threads, but again he could not prove this. His delicate observations on the behaviour of spindle fibres were later con- firmed by electron microscopy. Division during development In his attempts to present a general interpre- tation of mitosis that was valid for all organ- isms, Flemming also studied division during the development of spermatozoa; he described this in a lecture in 1888 (REF. 30). Although Flemming failed to recognize the division?.) The methods that Flemming had developed allowed him to recognize a fibrous scaffold in the nucleus, which could easily be stained and was therefore named Chromatin (?stainable material?). Some other structures remained unstained and were therefore termed Achromatin. These results led, in 1882, to the publication of Flemming?s comprehensive book Zellsubstanz, Kern und Zelltheilung (?Cell substance, nucleus and cell division?) 22 , which became the foundation for all further research into mitosis. Although Schleicher 23 had pro- posed the name Karyokinesis for this process, Flemming decided to use a more exact term, and he called the observed alterations within the nucleus Karyomitosis (meaning threadlike metamorphosis of the nucleus). He christened the arrangements of the nuclear threads Mitosen. Only afterwards, in 1888, did Heinrich Wilhelm Waldeyer 24 coin the term Chromosomen (?chromosomes?, meaning stain- able bodies) for Flemming?s nuclear threads. Flemming described the processes in the nucleus as we know them today, and he made a distinction between the ?progressive? and ?regressive? phases of cell division (FIG. 3). The progressive phase started with the appearance of the threads in the nucleus of the mother cell and continued as far as the arrangement of the threads in the centre of the cell. The regressive phase, by contrast, began with the separation of the threads into two groups and ended with the reappearance of the daughter nuclei. Although Flemming had the correct idea that the chromatin network in the ?resting? nucleus transforms into the threads (chromo- somes) ? thereby representing continuity of the nuclear material ? he did not have the techniques or equipment to prove this. The objective lenses of his microscope were com- posed of lenses with different refractive indices, but these lenses contained many aber- multiplication, Flemming showed that the scaffold and network within the nucleus transformed into ?threads?, which then sepa- rated into two groups. These two groups, in turn, formed two skeins, from which the scaffold of the nuclei reappeared. By carefully studying wounds and scars, Flemming and his students found an accumulation of divid- ing cells in these tissues, and concluded that the regeneration of tissues and organs occurs by cell division 16 . At that time, no general repertoire of his- tological methods existed ? indeed, one of the first monographs on histological meth- ods, by Alfred Fischer 17 , was not published until the end of the nineteenth century. In this book, many studies of fixed cells were consid- ered to be based on artefacts, so Flemming had to spend a long time designing methods to facilitate his observations 18,19 .He experi- mented with various acids to find an appro- priate fixative for preserving the fine structure that he had seen in the living cells and finally used a mixture of chromic, osmic and glacial acetic acids, which was soon adopted by col- leagues and known as ?Flemming?s solution?. He tested haematein and haematoxylin for their usefulness as dyes, and also found that the addition of very low concentrations of picric, acetic or formic acid to the medium best brought out the structures of the nuclear scaffold and the fine structure of the proto- plasm (cytoplasm; BOX 1). Nuclear division In 1878 and 1879, Flemming published two important papers 20,21 , in the second of which he coined the term ?indirect nuclear division? because he had observed that a transformation of the nuclear content had to take place before fission could occur. (A cleavage of the nucleus and protoplasm ? which, until then, had been generally assumed ? was called ?direct nuclear Hooke discovers that cork is composed of little chambers, which he calls cellula (cells). Dumortier and von Mohl discover that cell multiplication occurs by binary fission. Van Leeuvenhoek observes levende dierkens (small living animals) in infusions of organic matter. Brown sees ovoid bodies in cells and coins the term ?nucleus?. Flemming (temporarily) summarizes his results in a book. The term mitosis for indirect nuclear division is born. Remak recognizes deformations of the nucleus as preparation for division. Schneider shows mitotic figures in spermatogenesis of platyhelminths. Schleiden and Schwann state that all plants and all animals are composed of cells. De novo formation of cells from intercellular substance. Strasburger presents the detailed drawings of dividing plant cells but still sticks to de novo cell formation. B�tschli detects fine filaments especially at the poles; the spindle is recognized. Flemming decides to name cell division indirekte Zellteilung (indirect cell division) to distinguish it from direkte Zellteilung (direct cell division), which is less frequent. The scaffold in the nucleus is the Chromatin. Flemming gives first descriptions of cell division in animals. 1665 1682 1832/35 1833 1835 1838/39 1873 1874?1876 1875 1876 1879 1882 Timeline | The origins of research into mitosis � 2001 Macmillan Magazines Ltd PERSPECTIVES Leopold?Carolinae Nat. Curios (part 1) 16, 217 (1832). (Cited in reference 36.) 7. von Mohl, H. �ber die Vermehrung der Pflanzenzellen durch Theilung (Inaugural dissertation, T�bingen 1835). 8. Remak, R. Untersuchungen �ber die Entwickelung der Wirbelthiere (G. Reimer, Berlin 1855). 9. Peters, G. Walther Flemming (1843?1905): sein Leben und sein Werk. Inaugural dissertation (doctoral thesis), Kiel (1967). 10. Brown, R. Observations on the organs and mode of fecundation in Orchidae and Asclepiadeae. Trans. Linn. Soc. (Lond.) 16, 685?743 (1833). 11. Purkinje, J. E. Symbolae ad Ovi Avium Historiam ante Incubationem (Leopold Voss, Leipzig, 1830). 12. Schneider, A. Untersuchungen �ber Plathelminthen. Jahrb. Oberhess. Ges. Naturwiss. Heilk. 14, 69?81 (1873). 13. Flemming, W. �ber die ersten Entwicklungserscheinungen am Ei der Teichmuschel. Arch. Mikrosk. Anat. 10, 257?292 (1874). 14. Flemming, W. Studien in der Entwicklungsgeschichte der Najaden. Sitzungsber. Kaiserl. Akad. Wiss. 71, 81?212 (1875). 15. Flemming, W. Beobachtungen �ber die Beschaffenheit des Zellkerns. Arch. mikrosk. Anat. 13, 693?717 (1876). 16. Flemming, W. Studien �ber Regeneration der Gewebe. Aus dem Anatomischen Institut Kiel 4?22, 23?42, 60?65, 76?102 (Bonn, 1885). 17. Fischer, A. Fixierung, F�rbung und Bau des Protoplasmas (Fischer, Jena, 1899). 18. Flemming, W. �ber das E. Hermannsche Kernf�rbungsverfahren. Arch. mikrosk. Anat.19, 317?330 (1881). 19. Flemming, W. �ber die Wirkung von Chrom?Osmium?Essigs�ure auf Zellkerne. Arch. mikrosk. Anat. 45, 162?166 (1895). 20. Flemming, W. Zur Kenntnis der Zelle und ihrer Theilungserscheinungen. Schr. naturwiss. Verein Schleswig-Holstein 3, 23?27 (1878). 21. Flemming, W. Ueber das Verhalten des Kerns bei der Zellteilung und �ber die Bedeutung mehrkerniger Zellen. Arch. Pathol. Anat. 77, 1?28 (1879). 22. Flemming, W. Zellsubstanz, Kern und Zelltheilung (F. C. W. Vogel, Leipzig, 1882). 23. Schleicher, W. Die Knorpelzellteilung. Ein Beitrag zur Lehre der Teilung von Gewebszellen. Arch. Mikrosk. Anat. 16, 248?300 (1879). 24. Waldeyer, H. W. �ber Karyokinese und ihre Beziehungen zu den Befruchtungsvorg�ngen. Arch. Mikrosk. Anat. 32, 1?22 (1888). 25. Flemming, W. Neue Beitr�ge zur Kenntnis der Zelle. Arch. Mikrosk. Anat. 37, 685?751 (1891). 26. B�tschli, O. Studien �ber die ersten Entwicklungsvorg�nge der Eizelle, der Zellteilung und die Conjugation der Infusorien. Abh. Senckenbergische Naturf. Ges. 10, 213?452 (1876). 27. van Beneden, E. R�cherches sur la maturation de l�oeuf et la f�condation. Arch. Biol. 4, 265?638 (1883). 28. Boveri, T. Zellen?Studien (Gustav Fischer, Jena, 1887?1900). 29. Flemming, W. Attraktionssph�ren und Zentralk�rperchen in Gewebs? und Wanderzellen. Anat. Anz. 6, 78?86 (1891). 30. Flemming, W. �ber die Entwicklung der Spermatosomen bei Salamandra (Kiel, 1888). 31. Flemming, W. Beitr�ge zur Kenntnis der Zelle und ihrer Lebenserscheinungen. Arch. Mikr. Anat. 20, 1?86 (1882). 32. Farmer, J. B. & Moore, J. E. S. On the maiotic phase (reduction-divisions) in animals and plants. Q. J. Microsc. Sci. 48, 489?557 (1905). 33. Flemming, W. Beitr�ge zur Kenntnis der Zelle und ihrer Lebenserscheinungen. Arch. Mikrosk. Anat. 16, 302?436 (1879). 34. Flemming, W. Beitr�ge zur Kenntnis der Zelle und ihrer Lebenserscheinungen. Arch. Mikrosk. Anat. 18, 151?259 (1880). 35. Belar, K. Beitr�ge zur Kausalanalyse der Mitose. Roux? Arch. Entw. Mech. Org. 118, 359?484 (1929). 36. Harris, H. The Birth of the Cell (Yale Univ. Press, New Haven, 1999). 37. Flemming, W. �ber Zellstrukturen. Anat. Anz. 16, 2?12 (1899). 38. Meves, F. Die Kondriomikonten im Verh�ltnis zur Filarmasse Flemmings. Anat. Anz. 31, 561?569 (1907). 39. Pernice, B. Sicil. Med. 1, 265 (1889). (Cited in Eigsti, O. J. & Dustin, P. Jr Colchicine in Agriculture, Medicine, Biology, and Chemistry (Iowa State Coll. Press, Ames, Iowa, 1955).) differences between the division of somatic cells and that of gametes, as he reported in his paper of 1882 (REF. 31) he had already observed the paired nature of the chromosomes in the early stages of spermatozoan development. In 1905, Farmer and Moore 32 reported the first descriptions of maiosis. Strasburger 8 assumed that the rod-like structures (chromosomes) were transversely split, and this was a source of strong controversy between him and Flemming. Flemming insisted ? and could prove ? that, in Metakinese or earlier, the threads were split longitudinally. He had already assumed 31,33,34 that one half of this longitudinally split pair was destined for one daughter cell, whereas the second half went to the other daughter ? a prediction that has turned out to be correct. Consequences of Flemming?s findings A host of papers appeared over the two or three decades after Flemming published his spectacular book on mitosis 22 . But research into mitosis then slowed down until around the 1920s, once Alfred Fischer?s book 17 had warned about the danger of studying arte- facts caused by fixation and staining. For example, for some time the spindle fibres had been considered to be coagulation arte- facts produced by fixation. In the mid-1920s, Karl Belar experimented with dividing sper- matocytes to find out the mechanics of chro- mosome transport and, in 1929, he pro- posed the stem body hypothesis 35 .A few years before the Second World War, a new age of mitosis research began. This was interrupted by the war ? especially by the holocaust and the emigration of many Jewish scientists from Germany. Flemming could not have foreseen the variety of disciplines that have come out of his work. First, of course, are the fields that are closely connected with the original mitosis research. Chromosome structure and function has become a special branch of this, leading to investigations of kineto- chores and telomeres for example, and even to the discovery of the function of the nucleolus. The combination of mitosis research with breeding experiments to explain Mendelian inheritance finally resulted in genetics and cytogenetics, which, in turn, led to gene manipulation, gene therapy, mutation research and the deci- phering of the genetic code. The spindle is still a structure of interest. Research is being done into its behaviour during division, into its function as an appa- ratus for transporting chromosomes, micro- tubules, tubulin, microtubule-associated proteins and motor proteins, and into ciliary movements, the centrosome (centriole) and mitotic poisons (used as cytostatic agents). Other fields include the ?uncontrolled? growth of cancer, and cell-cycle regulation. Last, Flemming?s research has also led indi- rectly to studies into programmed cell death, which starts with drastic changes in nuclear structure and cell-cycle regulation. Neidhard Paweletz is at Wilhelmsfelder Strasse 47/1, D-69118 Heidelberg, Germany. e-mail: 100.272955@germanynet.de Links ENCYCLOPEDIA OF LIFE SCIENCES Theodor Ambrose Hubert Schwann | Matthias Jacob Schleiden 1. Hooke, R. Micrographia (London, 1665). 2. van Leeuwenhoek, A. Letter no. 35, March 3, 1682. 3. Schleiden, M. J. Beitr�ge zur Phytogenesis. M�ller�s Arch. Anat. Physiol. Wiss. Med. 136?176 (1838). 4. Schwann, T. Mikroskopische Untersuchungen �ber die �bereinstimmung in der Struktur und dem Wachsthum der Thiere und Pflanzen (Verlag der Sander�schen Buchhandlung, Berlin, 1839). 5. Strasburger, E. �ber Zellbildung und Zelltheilung (Hermann Dabis, Jena, 1875). 6. Dumortier, B. C. Nova Acta Phys. -Med. Acad. Caesar. NATURE REVIEWS | MOLECULAR CELL BIOLOGY VOLUME 2 | JANUARY 2001 | 75 Waldeyer observes the stainability of the nuclear ?threads? during division. Thay are named Chromasomen (stainable bodies). Pernice recognizes colchicine as a mitosis inhibitor 39 . Flemming proves the presence of the small polar body in the ?resting? cell as well as in the dividing cell and names it Zentriole. Van Beneden and Boveri discover the centrosphere during division. Boveri calls it the centrosome. Flemming studies division in spermatogonia. Flemming discovers the ?midbody?. Farmer and Moore 32 study the ?reduction divisions? of gametes and call these divisions maiosis. 1883-87 1888 1888 1889 1891 1891 1905 � 2001 Macmillan Magazines Ltd "
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