High-performance microscope shows detail of pores in cell nucleus
The new imaging, pioneered by an Zürich University (UZH) research team headed by Professor Ohad Medaliait, gives a better picture of why certain molecules are allowed to pass through the nuclear pores while others are turned away.
"We discovered a previously unobserved structure inside the nuclear pore that forms a kind of molecular gate, which can only be opened by molecules that hold the right key," explains Medalia.
This "molecular gate" consists of a fine lattice, which enables small molecules to slip through unobstructed.
Molecules are transported into the nucleus or from the nucleus into the cytoplasm. In a human cell, more than a million molecules are transported in this way every minute.
In the process, special pores embedded in the nucleus membrane act as transport gates. These nuclear pores are among the largest and most complex structures in the cell and comprise more than 200 individual proteins, which are arranged in a ring.
They contain a transportation channel, through which small molecules can pass unobstructed, while large molecules have to meet certain criteria to be transported.
The imaging was achieved using cryo-electron tomography – a method to render cell structures three-dimensionally visible in their natural environment in high resolution using both electron microscopy and computer imaging.
The cells are shock-frozen in liquid nitrogen at -190°C.