Dictyostelium discoideum: more than meets the eye.
It’s tempting to think of amoebae as the single, fried-egg-shaped animal cells we learned about in biology at school – and when there’s plenty of food around, that’s pretty much right. But what happens when the food runs out? For the soil-dwelling Dictyostelium discoideum, things get a little weird.
These amoebae usually feed on bacteria and live quite happily as individual cells when food is plentiful. However, when there’s no bacteria around, the amoebae stick together, or ‘aggregate’, to form slug-like super colonies.
The job of these 4 mm ‘slugs’ is to migrate to a good spot, where they transform again, this time into fruiting bodies – tiny hand grenades filled with spore-like cells – that burst, transporting future amoebae to areas where more food is present, starting the cycle all over again.
Slug formation is triggered when the amoebae release a small molecule called cyclic AMP, which tells neighbouring D. discoideum cells to aggregate. Cyclic AMP is made from adenosine monophosphate (AMP), one of the nucleotides that make up DNA and an important signalling molecule in prokaryotes and eukaryotes.
Until now, despite decades of research, no-one knew what triggered the slugs into forming a fruiting body, but researchers from Dundee have shown that another cyclic nucleotide – cyclic di-GMP – provides the signal. The remarkable thing about this is that the molecule, which was discovered 25 years ago, was thought to be restricted to bacteria, so finding it in D. discoideum (a eukaryote) is a bit of a surprise.
The discovery of cyclic di-GMP a quarter of a century ago triggered a huge field of research, as it became clear that this small cyclic dinucleotide affects a huge range of processes in a wide variety of bacteria. This discovery breathes fresh life into the field, and it will be exciting to see whether cyclic di-GMP is used by more complex multicellular eukaryotes, and if so, what processes it controls.
Chen ZH, & Schaap P (2012). The prokaryote messenger c-di-GMP triggers stalk cell differentiation in Dictyostelium. Nature, 488 (7413), 680-3 PMID: 22864416