|
|
| |
No. 71 Swiss Pioneers in Science and Medicine |
|
R. Dahm It is a cold winter day in February. A young postdoctoral researcher training abroad writes a letter home. In it he describes what he has been up to in the laboratory, including an unusual observation he has recently made in one of his experiments. What seems like a commonplace occurrence in the life of any budding scientist was in fact a defining moment in the history of the life sciences. The year was 1869, the young postdoc was the Swiss doctor Friedrich Miescher, and what he related in his letter is one of the most far-reaching findings ever made: the discovery of DNA. At the time, Miescher was working under the guidance of Felix Hoppe-Seyler, one the of great biochemists of his age. Their laboratories were located in the former kitchen and laundry of an ancient castle in the old university town of Tübingen in southwest Germany. Though picturesque, from today's point of view the laboratories would seem hopelessly inadequate with their sparse and primitive equipment. Nonetheless, in the 19th century this was a top location where Hoppe-Seyler and his colleagues were making groundbreaking discoveries on the chemical basis of life.
This was the reason why the young Miescher had chosen to work with Hoppe-Seyler. After finishing his medical studies in his native Basel, he had decided against a career as a practicing physician and instead chose to investigate the chemistry of living beings. Little was known of the molecules that comprise animals, plants or fungi at that time. Physiological chemists, as biochemists were called then, were mainly trying to classify and characterize the different proteins, lipids and other compounds they could isolate from different tissues or species. But it was still totally unclear what drove the processes of life. Miescher was convinced that understanding the chemicals that make up animals would be the key to understanding how life works. And so he moved to Tübingen, a hub of the young discipline of physiological chemistry. In Hoppe-Seyler's laboratory, Miescher chose to work on leukocytes. He extracted these white blood cells from the pus on fresh surgical bandages. This choice of source material likely played an important role in Miescher's ultimate success. Most of his contemporaries were analyzing the composition of tissues or entire organs, but by starting with a single cell type that could easily be purified, Miescher had the advantage of dealing with a simpler mixture of molecules. Having isolated the cells by carefully washing the bandages, Miescher subjected them to various procedures to separate their chemical constituents. Initially, he focused on the different fractions of proteins and lipids, which he isolated and tried to characterize. In one of his experiments he noticed something unusual: a substance that did not behave like any of the molecules known at the time. In the letter he wrote on February 26, Miescher described his experimental findings: 'I could obtain precipitates that could not be dissolved either in water, acetic acid, very dilute hydrochloric acid, or in solutions of sodium chloride, and which thus could not belong to any of the hitherto known proteins.' Miescher had hit upon a substance with properties unlike those of anything known then. He was excited by his finding, but not even he could realize at that time what he had really achieved: Miescher had, for the first time, obtained a crude isolation of DNA. In an important insight, Miescher realized that this substance must come from the cells' nuclei. In the middle of the 19th century the nucleus was an enigmatic structure, and Miescher realized his discovery might provide a key to understanding it. But in order to characterize the new molecule better, he first needed to purify more of it. He therefore developed a protocol to separate nuclei from the surrounding cytoplasm. To achieve this he washed the cells repeatedly over a period of several weeks with diluted hydrochloric acid. To avoid degradation of the material during long washes, he performed this step at 'wintery temperatures'. The exact conditions under which Miescher worked are unknown, but it is easy to imagine him in his laboratory, behind the thick walls of Tübingen's castle with the windows open to the cold winter and the temperature in his laboratory barely above freezing. Miescher observed that nuclei isolated with this method behaved similarly to the unknown substance he had detected before, confirming that it did indeed reside within the nuclei. But the protocol did not yield enough of the novel substance to characterize it further, so it was necessary for Miescher to develop yet another method. Fortunately for Miescher, in 1868 the German physiologist Wilhelm Kühne had published a protocol that described how solutions containing the enzyme pepsin – which is secreted by the stomach to digest protein – break down the cytoplasm of cells, but not the nuclei. Miescher decided to expose his cells to pepsin to get rid of the cytoplasm. But to obtain the enzyme, he first had to rinse out pig stomachs with hydrochloric acid. The new protocol finally brought success. As a first step, Miescher washed the leukocytes with warm alcohol. This broke the cells up and stripped off some of the cytoplasm. To remove the remaining cytoplasm, he then exposed the nuclei to his pepsin solution, which digested all the proteins. After a few hours, a fine gray powder sank to the bottom of his beaker. As before, Miescher shook this sediment with ether and washed it several times with alcohol to get rid of the lipids. In alkaline solutions, the sediment dissolved, but when he added acid, a wool-like precipitate appeared again. Miescher had finally obtained his first clean preparation of DNA for analysis. Since he could precipitate the new substance by acidifying the solution, Miescher knew that it was an acid. His next step was to determine which elements it was composed of. In addition to carbon, hydrogen, nitrogen and oxygen – which are commonly found in organic molecules – he detected unusually high amounts of phosphorous, but little or no sulfur. This was in stark contrast to proteins and other molecules known at the time and the results convinced Miescher that he had indeed discovered a completely new type of molecule. He would later write: 'We rather have here entities sui generis [i.e. of their own kind] not comparable to any hitherto known group.' Since he had isolated the new molecule from the cells' nuclei, he named it 'nuclein'. Although the molecule has since been renamed, Miescher's original idea remains in today's designation: deoxyribonucleic acid. Having found nuclein in leukocytes, Miescher began to search for it in other cells and tissues too. And wherever he looked, he found it: in kidney, liver, testes, nucleated erythrocytes and yeast cells. This led him to state later that nuclein 'will prove equal in importance to proteins'. At this stage Miescher was clearly keen to publish his results. At the end of 1869, when Miescher had since moved to the University of Leipzig, he had finished drafting his first manuscript and was ready to send it to his mentor Hoppe-Seyler in Tübingen. In a letter to his parents dated December 23, 1869, he wrote: 'On my table lies a sealed and addressed packet. It is my manuscript, for whose shipment I have already made all necessary arrangements. I will now send it to Hoppe-Seyler in Tübingen. So, the first step into the public is done, given that Hoppe-Seyler does not refuse it.' Much to Miescher's disappointment, however, Hoppe-Seyler did refuse to publish his manuscript until he had a chance to verify Miescher's results himself. This decision on Hoppe-Seyler's part does not so much reflect a lack of trust in Miescher's work. Hoppe-Seyler had just founded a new journal and Miescher was hoping to have his article included there. To warrant the reputation of his journal, Hoppe-Seyler had to ensure that only work of the highest standards would be published. As it turned out, Miescher's paper would provide exactly that, but to be sure Hoppe-Seyler had to confirm his student's results. Finally, nearly a year later, Miescher received a letter from Hoppe-Seyler to say that both he and another student of his had reproduced the results and that they would be included in Hoppe-Seyler's Medicinisch-chemische Untersuchungen. Fishing for a Breakthrough After a brief spell in Leipzig, Miescher returned to Basel where he became a professor at the university and resumed his studies on nuclein. There he discovered that sperm cells, with their large heads packed to the brim with nuclein, were an excellent source of DNA. In Basel, with its annual migration of salmon through the Rhine, Miescher soon recognized that male salmon are full of sperm as they swim upriver to their spawning grounds. He would frequently get up in the middle of the night and spend the early hours of the day on the riverbank catching fish for his experiments. With this new source of nuclein, Miescher managed to purify much bigger quantities than he could produce in Tübingen. He used this material to perform some of his most accurate analyses of the properties of DNA. Miescher also worked hard to understand what role DNA played in the life of a cell. Even during his time in Tübingen, he had speculated that increasing the cell's DNA content might be required for cells to be able to proliferate. Later, when working on the presence of nuclein in sperm cells and oocytes, Miescher also speculated on a role in fertilization and heredity, but ultimately rejected the idea. Instead he favored a function for nuclein in storing phosphorous inside the cell. It is tragic for Miescher that he came so close to uncovering the function of the molecule he had discovered. Ultimately though his thinking was trapped in his intellectual environment, and it fell to others to link DNA with heredity. Based on the pioneering studies by Miescher and subsequent work by others, scientists had concluded by the mid-1880s that nuclein might be the molecule that stores hereditary information. But in the early 20th century scientists increasingly shifted their attention to proteins as the candidates for this function. DNA, with its composition of only four different building blocks, was seen as too simple to encode the complexity of life. Proteins on the other hand, which consist of 20 different amino acids, appeared better suited for this task. It was not until 1944 that experiments by Oswald T. Avery, an American molecular biologist, and his co-workers showed conclusively that DNA is the molecule that transmits genetic information. Finally, in 1953 James Watson and Francis Crick deciphered the double helix structure of DNA and, nearly a century after Miescher had discovered the molecule, the genetic code was cracked. Now scientists could, for the first time, decode the information contained in DNA. Birth of an Icon Friedrich Miescher died in 1895 with a feeling of not having fulfilled his scientific ambitions. But his discovery was the foundation upon which an entirely new discipline of biology was built: molecular genetics. Our understanding of how DNA works and our ability to manipulate it have since transformed not only the life sciences and medicine, but also pervaded numerous other areas of our lives. Modern forensic science would be unthinkable without DNA analyses; food inspectors use it to detect ingredients which are prohibited or to trace their provenance; it allows conservationists to check whether products contain materials from protected species; and even artists are now using DNA or its double-helical shape in their works. The molecule Miescher found behind the ancient walls of Tübingen castle truly has become the icon of the modern life sciences and one of the great symbols of our time. Further Reading Dahm R: Friedrich Miescher and the discovery of DNA. Dev Biol 2005;278:274–288. Dahm R: Discovering DNA: Friedrich Miescher and the early years of nucleic acid research. Hum Genet 2008;122:565–581. Dahm R: From discovering to understanding: Friedrich Miescher's attempts to uncover the function of DNA. EMBO Reports 2010; 11:153–160. Maderspacher F: Rags before the riches: Friedrich Miescher and the discovery of DNA. Curr Biol 2004;14:R608. Miescher F: Ueber die chemische Zusammensetzung der Eiterzellen. Medicinisch-chemische Untersuchungen 1871; 4:441–460. Wolf G: Friedrich Miescher, the man who discovered DNA. Chem Herit 2003;21:10–11 and 37–41.  Ralf Dahm University of Padova Dr Dahm is currently Director of Scientific Management at the Spanish National Cancer Research Centre (CNIO) in Madrid and Visiting Professor at the University of Padova. He speaks and writes extensively on popular science. www.ralf-dahm.com |
The Friedrich Miescher Institute for Biomedical Research In the city of Basel, Friedrich Miescher's hometown, the memory of the pioneering physician is kept alive at the Friedrich Miescher Institute.
Founded in 1970, the institute is a crucial part of Basel's globally important biomedical industry. Now associated with the Novartis Research Foundation, the institute carries out fundamental research to understand what causes diseases at a molecular level.
Much of the institute's research is devoted to epigenetics, the study of how the expression of the same sequence of DNA
is modulated by the cellular
machinery to produce different phenotypes.
Susan Gasser, director of the FMI, sees this work as fitting for an institution named after the man who first speculated that DNA is the basis of heredity. She says: 'The innovative aspect of epigenetic research is very much in line with the pioneering spirit of Miescher, and the focus on genetic inheritance – and epigenetic modification of genetic inheritance – creates tight links to the famous Basler.'
The FMI aims to be 'intellectually daring' which, as Gasser puts it, means 'working at the frontiers of our knowledge, trying to link and apply novel concepts from different areas of expertise.'
The institute also donates the Friedrich Miescher prize, which is given each year to a particularly brilliant young researcher, as selected by the Swiss Society of Biochemistry. |
 © 2010, S. Karger AG, Basel. All rights reserved. |
