UFMG / YALE / NCBReticulum of the nucleus (red arrows) of liver cells: autonomyUFMG / YALE / NCB
One single piece of research knocks down two myths at the same time. The first: in the nucleus of cells there isn’t just the chromosomes, made up of proteins and DNA, as it was thought for at least fifty years. Within there is also, as the Brazilian and American researchers have discovered, a network of tubes that store calcium – a chemical element essential for the working of the cell. “This is the first time that anyone has shown that the nucleus contains its own organelles”, comments Maria de Fátima Leite, a researcher at the Federal University of Minas Gerais (UFMG) and the co-author of this work, published on the 22nd of April in the on-line edition of Nature Cell Biology. Maria de Fátima and Michael Nathanson, from Yale University in the United States, have verified that such organelles – or compartments called endoplamastic reticulum – at least occur in liver cells. “It is probable that the cells of the heart, muscles and nervous system also possess this structure”, she adds.
The second undone idea is that the nucleus will receive calcium only from the cytoplasm, the gelatinous portion that occupies the space between the nucleus and the cell’s external membrane. It is in the cytoplasm that compartments with various functions are found, an example being the smooth endoplasmatic reticulum, a type of bag that entraps the calcium. The team’s finding suggests that it is possible that the calcium passed through the membrane of the nucleus but there is no longer any way of denying the self-sufficiency of the nucleus regarding this chemical element, essential in regulating muscular contraction, in heart beating , in hormones secretion, in cell multiplication and differentiation and in the so-called neuronal plasticity – the capacity of the brain to create alternative routes to maintain the body functioning or to rescue memory. In the nucleus, the calcium could also change the structure of the DNA molecule, and activate or deactivate genes.
Cited in the section Editors’ Choice of the magazine Science of the 9th of May, the paper by the researchers from UFMG and Yale helps to understand how one single chemical element – even though it is abundant in the interior of the cells – can manage to regulate so many cellular functions. The calcium is released selectively – only when the endoplamastic reticulum is activated – and thus determines one or other answer from the nucleus. Afterwards, conducted by transporting molecules, the calcium makes the return trip: again cuts across the pores of the membrane of the network of tubes and remains lodged within until it will be requested once again. “If it remains free in the nucleus or in the cytoplasm”, Maria de Fátima says, “the calcium will set off a series of chemical reactions that could lead to the death of the cell.”
In order to discover the depositories of the calcium, the researchers used proteins that work as fluorescent probes that, through chemical affinity, adhere to the endoplasmatic reticulum. They only arrived at these conclusions and saw the calcium depositories of the nucleus because they made use of a two photon microscope, which, besides the very high resolution, causes less damage to the cells than using other techniques.
There is very little of this type of equipment in the world – one of them is in Nathanson’s laboratory, with whom the Brazilian researcher began to collaborate some two years ago. The work that they carried out together does not only suggest alterations in textbooks, in which the nucleus appears with the only space being for the chromosomes. It will also affect research for medicines – such as those used against hypertension or in the regeneration of the liver – whose side effects might be minimized with a measure that acts in a more precise manner on the calcium of the nucleus or on the cytoplasm of the cells.
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