European researchers have sparked debate by claiming that cell nuclei could contain liquid crystals. The hypothesis is supported by experiments revealing that DNA transcription is possible in such environments, says the team from the UK and Germany.
"Isolated cell nuclei exhibit an optical property known as birefringence that is characteristic of liquid crystals."
George Attard from the University of Southampton, UK, and colleagues have shown that DNA can be transcribed into RNA within a liquid crystalline phase formed by phospholipids. Moreover, they found that isolated cell nuclei exhibit an optical property known as birefringence that is characteristic of liquid crystals. The researchers say that together these results 'raise the possibility that lipids might form organised structures in the nucleus in vivo
Birefringence suggests that phospholipids are ordered in the cell nucleus
Attard says his research is 'off the wall', and adds that mainstream researchers are reluctant to accept his views. Indeed, Roel van Driel, an expert in nuclear organisation from the University of Amsterdam, the Netherlands, is not convinced. He points out that Attard's group freeze-dried the studied nuclei, which will have caused major structural rearrangements. Therefore there is no evidence that living nuclei show birefringence, he says. Attard accepts this, but adds: 'We have X-ray data from non-freeze-dried nuclei which are consistent with long-range ordering.'
Van Driel also says that for living nuclei to show birefringence, chromatin - a complex of DNA and proteins - would have to be ordered on the length scale of the nucleus, which it is not. Attard counters that chromatin could adopt any degree of structural ordering, or none at all, within a liquid crystalline phase, but that these phases would still cause birefringence.
Despite criticism, Attard says that it is 'likely' that nuclei are in a liquid crystalline state. Cell nuclei are rich in phospholipids and these molecules are known to self-organise into structures, for example membranes, he explains. Based on the intermolecular forces, 'you would be more surprised to find that nuclei are not liquid crystalline rather than the reverse,' says Attard.