Transportation selection mechanism between nucleus and cytoplasm in the nuclear pore complex Approach from morphology

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All eight kinds of surfaces of nuclear membranes (four true surfaces of the outer and inner nuclear membranes, four fracture faces of the outer and inner nuclear membranes) in the rat pancreatic acinar cell were exposed by adjusting the density and the kind of fixatives and/or by controlling the density of antifreeze solution at the freeze cracking process. The exposed surfaces were ion-coated with osmium and they were investigated with high-resolution scanning electron microscope(SEM).As the proteins consisting nuclear pore complex(NPC) were tend to disappear at the maceration treatment process with 0.1% osmium solution, the observation of the nuclear pore without proteins of NPC about 45-65 nm in diameter could be possible both from the cytoplasm side and nucleus side. The membrane surrounding the nuclear pores rose slightly like the bank, and it seemed to form a ring of about 90 nm in diameter on the true surface of inner nuclear membrane.SEM observation from the cytoplasm side reve … More aled that eight particles consisting the cytoplasmic part of NPC were not spherical but ovoid in shape. Since these particles disappeared rather easily at the maceration treatment process, it became possible to observe the true surface of outer nuclear membrane without the particles. The surface was smooth and flat appearance, and so it seemed to remain intact. This result indicates that the particles are situated on the true surface of outer nuclear membrane having little connection with the membrane.The size of transporting material ("central plug" or "cargo" or "cargo and transport factors") was about 25-30 nm in diameter. The central part of NPC surrounding the transporting materiel formed a central ring of about 10-35 nm in inner diameter, 45-65 nm in outer diameter. It was composed of sixteen particles. The ring like structure of about 45-65 nm in inner diameter and about 90-100 nm in outer diameter situated in the perinuclear space was also composed of sixteen particles. The both composition protein particles in the perinuclear space and in the center of nuclear pore seemed to form a ring connecting tightly to each other across the membrane probably in the form of dimmer units. Less