Researchers found a never-before seen structure in the cell nucleus through an ultra high-precision microscope.

Biochemists at the University of Zurich used cryo-electron microscopes to obtain a high-resolution display of the pores in the cell nucleus. The microscopes revealed the newly-discovered structure found inside the nuclear pore forming a "molecular gate."

According to Professor Ohad Medalia, a pioneer of cryo-electron microscopy and the head of this research, the gate can only be opened by molecules that "hold the right key."

In the study, shock-frozen frog oocytes were used. Through the cryo-electron microscopes, Medalia and his team were able to display the very tiny pores in the nucleus. The pores have a diameter of more or less a ten-thousandth of a millimeter. These pores bear the molecular gate or "spoke ring" found between two other rings and extending to inside the pores. A lattice in the gate allows small molecules to move around unobstructed.

In a human cell, over a million molecules travel into the nucleus every minute. Pores embedded in the nucleus membrane then become transport gates. Holding more than 200 million proteins, these pores are among the largest and most complex of structures in the cell.

The discovery of this microscopic structure in the cell nucleus may lead to future studies and further breakthroughs in biochemistry. A better understanding, for example, of why certain molecules can travel through the pores, while others move away, can be obtained. Diseases that are affected by defective transportation to the nuclear ores, like intestinal, ovarian and thyroid cancer, can also be further researched.

"Polara" and "Titan Krios" electron microscopes can be purchased through support received from the Maxi Foundation. Currently, they are operated along with UZH's Center for Microscopy and Image Analysis.

Cryo-electron microscopy is a form of transmission electron microscopy, where samples are studied at cryogenic temperatures. It has started to become popular because it allows researchers to observe specimen in their natural environment — when they have not been stained or fixed. Cryo-electron microscopy has come out as steadily developing in 2014, when it allowed almost-atomic resolutions to be obtained.

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