Biologia celular: a nova anatomia celular que deixaria Darwin de queixo caído!!!

quinta-feira, dezembro 01, 2011

Cell biology: The new cell anatomy

A menagerie of intriguing cell structures, some long-neglected and others newly discovered, is keeping biologists glued to their microscopes.

Roberta Kwok

30 November 2011

In 2008, Chalongrat Noree faced an unenviable task: manually surveying hundreds of yeast strains under a microscope. Each strain had a different protein tagged with a fluorescent label, and Noree, a graduate student at the University of California, San Diego, was looking for interesting structures in the cells.

But it wasn't long until Noree's labour yielded results: within a month, he began finding a wide variety of proteins assembling into clusters or long strands. “Imagine every week you found a new intracellular structure,” says Jim Wilhelm, a cell biologist and Noree's adviser. “If it were a slot machine, it would be paying off every other time you pulled the handle.”

These days, textbook diagrams of cell structures such as the nucleus, mitochondrion, ribosome and Golgi apparatus are beginning to seem out of date. New imaging techniques, genome data, interest from disciplines outside cell biology and a bit of serendipity are drawing attention to an intricate landscape of tubes, sacs, clumps, strands and capsules that may be involved in everything from intercellular communication to metabolic efficiency. Some could even be harnessed for use in drug delivery or in synthesis of industrial products, such as biofuels.

Some of these structures have been known for decades, whereas others have only recently come to light. Wilhelm's team, for instance, has found six kinds of filament that either had never been described, or had been largely passed over. “You figure, how many structures could have been missed in the cell?” says Wilhelm. “Apparently, a lot more than you would imagine.”

Lines of communication

One structure that is receiving fresh scrutiny is the membrane nanotube: a thin thread of membrane suspended between cells. In 2000, Amin Rustom, then a graduate student at Heidelberg University in Germany, was using a newly acquired dye to look at rat tumour cells under a fluorescence microscope. But he decided to skip some washing steps in the protocol. “He said, 'I saw something — I don't know what it is, but it looks interesting',” recalls his former adviser, Hans-Hermann Gerdes, a cell biologist now at the University of Bergen in Norway. The tubes that Rustom had noticed were so straight that Gerdes initially wondered if they were scratches on the dish.

The team concluded in a 2004 study1 that the structures, which could span the distance of several cells, were channels that could transport small cellular organelles. That same year, Daniel Davis, a molecular immunologist at Imperial College London, and his colleagues proposed that immune cells might send signals to each other along such tubes2. At the time, Davis recalls, “There would always be people in the audience who would say, 'I saw those strands in the late 1970s or 80s'.” But earlier observers paid little heed to the tubes.

The 2004 reports prompted more studies, which have found nanotubes in many types of mammalian cell. Davis's team found that nanotubes could help certain white blood cells to kill cancer cells, either by acting as a tether that draws the cancer cell close or by providing a conduit for delivering lethal signals3. Nanotubes can also conduct electrical signals, which might enable cells to coordinate during migration or wound healing, according to a 2010 study by Gerdes and his colleagues4. HIV and prions — infectious, misfolded proteins — may even travel along the tubes5, 6.

Some researchers are sceptical that nanotubes can form open channels. “It's not clear that there's a real continuous tunnel,” says Jennifer Lippincott-Schwartz, a cell biologist at the US National Institutes of Health in Bethesda, Maryland. And so far, nanotubes have been studied mainly in cell culture. Blocking nanotube formation in living organisms might give clues to their importance, says Davis. But such manipulations often disturb other crucial processes.



A cada vez que os cientistas descobrem complexidades em sistemas biológicos, mais complexidade ainda está para ser descoberta que o paradigma biológico evolucionário atual se mostra falido no contexto de justificação teórica: Darwin não explica! Ponto final!!!