Friday, May 18, 2007

What science is not

From an extract of the book The invisible sex: Uncovering the true roles of Woman in Prehistory (review in Nature 3rd of May issue).

"science is not truth; it is, instead, a method for diminishing ignorance"

Wednesday, May 16, 2007

A 3D model of human breast cancer

This has been covered in a few places like the BBC and ScienceDaily. It seems that some researchers at Queen Mary College in London have recently come with a non animal 3D human breast cancer model.

This is interesting at more than one level. Their research was funded by a research charity (Dr Hadwen Trust) that supports the development of methods that avoid animal experiments. Working with rats is not that satisfactory for ethical reasons and also because there are many cases in which the results of rat experiments cannot be extrapolated to humans (seems we are not so similar in some respects after all). It is also much more realistic than just taking some human cancer cells and studying them on a petri dish.

Being capable of performing experiments using realistic 3D models quickly and efficiently is one of the holy grails of theoreticians since it would make experimental validation of our models much easier (confusingly enough what theoreticians call model, eg, equations or computer rules, is not what experimentalists understand as a model, eg. rat, arabidopsis or drosophila). This validation is quite complicated as I have already mentioned in another post. Making this validation easier and more convenient will go a long way in terms of making our work more reliable and quantitative.

Monday, May 14, 2007

Somatic and non somatic evolution

Many ecologists study evolution of the non somatic kind. That is, evolution that happens as a consequence of mutations in the germ line of multicellular organisms during reproduction. The evolution of cancer is of the somatic kind. This means that it affects cells of the soma, the ones that are not transmitted to the offspring.

Some time ago I got this paper from Crespi and Summers (nicely enough, publicly available). I will probably talk about this paper, entitled Evolutionary biology of cancer (and presented to a readership of ecologists) some other time but I liked a table in which they compare somatic and non somatic evolution.

Phenotypic variation. In most ecosystems of multicellular organisms variation is attained through genetic recombination (sexual reproduction) and mutation. In a tumour we also have to consider also genomic instability (a hypothesis by which some individuals have a higher probability of mutation) and epigenetic alteration (the environment also affects the behaviour of cells in ways that could make tumour progression to cancer more or less likely).
Selection. In most ecosystems it means dealing better with competitors, avoiding predators, parasites and producing many fit successors. In a tumour means being good at competing for resources with other cells (tumour or otherwise), avoiding the immune system and coping with environmental signals designed to maintain homeostasis.
Drift. That is similar in both types of evolution.
Inheritance. In many cases that involves the transmission of genes from parents to offspring through sexual recombination. In tumours there is no sexual reproduction.
Result. In most ecosystems the result is adaptation across generations. In a tumour the end results is in many cases the death of the individual and thus of all the cells in the body, including the cancer cells.

I think that this is a quite interesting and useful comparison of evolution although I am not sure I agree with all the differences suggested. In my view the evolution in a tumour does not differ much from other types of evolution. For instance, epigenetic changes do play a role in other ecosystems asides from cancer. Genetic instability is not a source of variation, genetic mutations are (genetic instability just makes genetic mutations more likely). Also the fact that tumour cells reproduce asexually is not a big difference with more conventional ecosystems. At the end of the day most of the biomass of the planet is made of bacteria that reproduces asexually. What it is true is that as far as we know, the end result of cancer evolution is either the end of the cancer itself or the end of the individual that hosts the cancer and thus the end of the cancer cells. Thus the only way tumour cells have to be successful is to evolve in such a way that the life of the host is not threatened (you can call that tumour sustainable growth).