Transmission electron microscopy of nuclear matrix and its proteins

We report about Transmission Electron Microscopy (TEM) of the nuclear matrix and its proteins. Using immunoelectron microscopy, we have detected the presence of lamins and the nuclear mitotic apparatus protein (NuMA) in nuclear matrices isolated from rat normal hepatocytes (NH) in the presence of an RNase inhibitor and after RNA digestion. The results were compared with those of nuclear matrices isolated from persistent hepatocyte nodules (PHN). In NH, immunoelectron microscopy shows that lamins and NuMA preferentially localise within electrondense domains of the internal nuclear matrix. After RNA digestion NuMA undergoes a sharp depletion, while lamins A and C increase in electrontransparent regions and a thin web of lamin protofibrils, which connect the electron-dense regions, are unmasked. Fourier filtering of the images shows that lamin epitopes are arrayed both in locally ordered clusters and in quasi-regular rows. In PHN, the nuclear matrix undergoes changes both in morphology and in protein composition. While the islands of lamin lattice are lost total expression both of lamins A/C and B is not affected. Vice versa expression of NuMA undergoes a statistically significant decrease with consequent reduction of the dimension of dense regions observed by electron microscopy. These results suggest that the organisation of the internal nuclear matrix, observable by TEM, plays an important role in carcinogenesis process.