In 1947, Ellsworth C. Dougherty and Hermione Grant Calhoun wrote a letter to the journal Nature in which they shared their reasons for believing Rhabditid nematodes to be a useful, facile genetic model system. This letter is one of the defining documents of the C. elegans field, and it’s still interesting to read 66 years later.
A PDF of the original letter is presented in the Hobert lab’s very nice resource, “How the Worm Got Started”.
In the terse Nature reference style, the names of the books and articles Dougherty and Calhoun cited are omitted, and the journal names are highly abbreviated. I have sleuthed these down and where possible provided links to the original articles on the Biodiversity Heritage Library and other sources.
References breakdown:
The letter in its entirety, with added hyperlinks and annotated/corrected bibliography, is below:
THE free-living nematodes of the sub-order Rhabditina are widespread in the soil[1] and relatively easily cultivatable[2–4] on nutrient agar in the presence of bacteria and have short life cycles (3–7 days from hatching to sexual maturity), with adult sizes up to 3mm. in length. They offer, in our estimation, certain very interesting possibilities for the study of basic genetic phenomena—morphological, cytogenetic and physiological.
The particular morphological significance of these forms is related to the phenomenon of cellular constancy, or eutely, which the phylum Nematoda (along with the other aschelminth phyla) exhibits for some or all somatic cells. Therefore, the free-living nematodes, containing at most a few hundred somatic nuclei in cells and syncytia, offer material in which mutations affecting structural components may well be interpretable in terms of cellular morphology, rather than only in terms of organ morphology and gross structure.
The cytology of sex cells of various species of the genus Rhabditis Dujardin (1844) has been studied by a few workers [5–11], and has revealed some very interesting sex-patterns. Diploid numbers of 10–24 chromosomes are known for the females and hermaphrodites of different species; the males, where known, are the heterogametic sex with an XO sex-chromosome pattern. Some species are dioecious, usually with approximately equal numbers of males and females; others are composed of hermaphrodites of female form and much rarer males, or no males at all; and a few consist only of thelytokous females. Certain dioecious and many hermaphroditic species use their sperm only to initiate development; the sperm confers its centrosome, but not its nucleus, on the ovum [5,7,8]. In some of these species pairing and reduction of chromosomes nevertheless occurs in meiosis; the diploid number is reconstituted with the failure of a second meiotic division to occur. Sex-determination is apparently effected by an unusual regulation of X-chromosome behaviour in meiosis. With simple chromosome numbers these forms should be good cytogenetic material; and with their unusual sex-patterns a considerable versatility in the detection and manipulation of mutations should be possible.
Another important consideration is the possibility of studying physiological mutants. As a result of the work of Kidder and Dewey[12], it is now possible to grow at least one organism of animal nutrition (the ciliate Tetrahymena geleii) on an almost completely chemically defined medium (consisting of inorganic salts, glucose, vitamins, amino-acids, purines and pyrimidines, and one unknown growth factor). It seems certain that the near future will see a completely known synthetic medium for this form. Through the use of a chemically defined medium the possibility arises that the new concepts of physiological genetics developed by Beadle[13] may be tested on a differentiating organism. Kidder and Dewey’s work suggests a valuable lead for the development of a chemically defined medium for species of Rhabditis.
We feel that, with eutely, good cytological features, and convenient sex patterns, together with promising cultural and nutritional aspects, the soil-dwelling nematodes offer attractive possibilities for a correlation and precise interpretation of the morphological and physiological genetics of a simple, differentiating organism. Such a simultaneous approach is being attempted in this laboratory. We are presenting the foregoing discussion in the hope of stimulating others to work on the same problem.
Ellsworth C. Dougherty
Hermione Grant Calhoun
Division of Medical Physics,
University of California,
Berkeley,
Aug. 18 (1947)
1. Chitwood,Benjamin Goodwin, and May Belle Hutson Chitwood. “An Introduction to Nematology”. Monumental Printing Co. (1937)
2. Dotterweich, Heinz. “Die Zuchtung von Rhabditis teres (A. Schn.) fur physiologische und genetische Untersuchungen.” Zoologischer Anzeiger 122, 266 (1938)
3. Stephenson, William. “On the culturing of Rhabditis terrestris n.sp”, Parasitology 34, 246 (1942)
4. Briggs, Margaret Poole. “Culture Methods for a Free-Living Soil Nematode”. (Masters Thesis, Stanford University 1946)
5. Krüger, Eva. “Fortpflanzung und Keimzellenbildung von Rhabditis aberrans, nov. sp.“. Zeitschrift für wissenschaftliche Zoologie 105, 87 (1913)
6. Hertwig, Paula. “Abweichende form der parthogenese bei einer Mutation von Rhabditis pellio”, Archiv für Mikroskopische Anatomie 94, 303 (1920) (special Festschrift issue commemorating their father Oskar Hertwig’s 70th birthday. She and her brother Günther Hertwig both have an article.)
7. Bělař, Karl Franz Josef. “Ueber den Chromosomenzyklus von parthenogenetischen Erdnematoden (vorl. Mitt.)”. Biologisches Zentralblatt, 43, 513 (1923)
8. Bělař, Karl Franz Josef. “Die Cytologie der Merospermie bei freilebenden Rhabditis-Arten”. Zeitschrift für Zellen- u. Gewebelehre, 1, 1 (1924)
9. Honda, Hikokuro (本多彦九郎). “Experimental and cytological studies on bisexual and hermaphrodite free-living nematodes, with special reference to problems of sex”. Journal of Morphology and Physiology, 40, 191 (1925) (note: NOT Honda, K. — the original is mistaken here.)
10. Nigon, Victor Marc, Comptes Rendus des Séances et Mémoires de la Société de Biologie et des ses Filiales, 137, 40 (1943)
11. Nigon, Victor Marc, “Le déterminisme du sexe chez un Nématode libre hermaphrodite: Rhabditis dolichura Schneider”. Bulletin de la Société Zoologique de France, 71, 78 (1946)
12. Kidder, George W., and Dewey, Virginia C., “Studies on the biochemistry of Tetrahymena. 5. The chemical nature of factors I and III.” Archives of Biochemistry, 8, 293 (1945)
13. Beadle, George Wells. “Biochemical Genetics”. Chemical Reviews, 37, 15 (1945)