Sunday, April 4, 2010
Sunday Spinelessness - A Nobel Prize Winning Insect
I think invertebrates are important. The 95% of animal species that don’t have a backbone are not simply the base of the animal kingdom’s pyramid, they are the little creatures that run the world. A third of the planet’s food production relies on honey bees, collembola and corpse-feeding insects turn dead tissue into living tissue and coral reefs can turn the nutrient-poor tropical seas into submarine rainforests. There are even a couple of invertebrate animals that have won the Nobel Prize.
Drosophila melanogaster has probably taught us more about genetics than any other animal on earth. In the wild D. melanogaster larvae develop on rotting fruit so, just like the flesh-flies that were featured here a couple of weeks ago, they are faced with the problem of having to complete their entire developmental program in the short period of time the fruit they are born in is a viable food source. Thanks to these environmental constraints, D. melanogaster has a very short life cycle. Under optimal conditions they can go from egg to adult in a week. This remarkable developmental haste means drosophilists can run genetic experiments that cover many generations in a few months, and they can run many replicates of these experiments because each of them takes up about this much space:
Drosophila has been kept in laboratories since the the turn of the 20th Century but T.H. Morgan was the first person to put Drosophila at the forefront of genetic research. Morgan was an embryologist by training and, like a lot of embryologists then and now, he became interested in a school of evolutionary thought called mutationism. As the name suggests, the mutationists argued that one-off mutations were the creative engine of evolution, relegating natural selection to weeding out maladaptive mutants. In order to test the creative power of mutation Morgan grew up generation after generation of Drosophila and bombarded them with anything he thought might mutate them; radium, salts, sugars, acids, bases and even centrifugal force. Two years of this mutational bombardment got Morgan nowhere, he could induce changes in his flies but none that would be stably passed on. In 1910 he found a single white eyed male.
There is a story, which I can't find repeated by reliable sources, that holds that Morgan took the first white eyed male home with him in jar and slept with the jar next to his bed that night. I don't know if that story is true but that one fly does have a treasured place in the history of genetics. By crossing it to normal eyed (what geneticists call "wild type") females he was able to show that the genetic factor that made the fly's eyes white was part of the sex determining chromosome. For the first time a gene had been shown to be reside on a chromosome. A few years later he showed that multiple genes are arranged in linear fashion along chromosomes by demonstrating crossing over between the white eye gene and another called rudimentary. At Otago second year geneticists repeat Morgan's experiments, so this picture, sorting flies under a binocular microscope, will be familiar to anyone whose been through the program. (it will probably also bring back memories of escaped flies and a whiff of the (dilute) ether used to knock the files out...)
Morgan was awarded the Nobel Prize in 1933, in 1948 Drosophila research got another Nobel, this time to Hermam Muller for showing X-ray radiation could induce mutations. Geneticists have continued to use Drosophila as a model organism, perhaps most usefully in untangling the genetic interactions that underly the development process. In 1980 Christiane Nüsslein-Volhard and Eric Wieschaus presented the results of a mutational screen; that is, they mutated Drosophila stocks at random and recorded the developmental phenotypes that resulted. Nüsslein-Volhard and Wieschaus identified 15 genes involved with the very early stages of development. In quick time Drosophilists mapped that those genes to chromosomes and worked out how their products combined to pattern a developing embryo. Nüsslein-Volhard and Wieschaus' work laid the ground work for one of the most staggering findings of modern biology, almost all the genes that help shape the Drosophila embryo have counterparts in the human genome that play similar roles in our development. An insect can be a useful model for human development and disease genetics. Nüsslein-Volhard and Wieschaus were awarded the Nobel Prize in 1995, the third Nobel for work on Drosophila.
A big thanks to Sarah Morgan, one of Otago's fly pushers, for the photos that illustrate this post. Sarah's off to the US of A this week to show off her research at The Big Drosophila Meeting in Washington DC so she will probably have some less historical Drosophila science to talk about in the next little while...
Nüsslein-Volhard C, & Wieschaus E. (1980) Mutations affecting segment number and polarity in Drosophila. Nature, 287(5785), 795-801. PMID: 6776413
Rubin GM, & Lewis EB. (2000) A brief history of Drosophila's contributions to genome research. Science, 287(5461), 2216-8. PMID: 10731135
So, has news that the name Drosophila is being taken away from your fly made it to the meeting yet ;)
The last ever Drosophila Research meeting...