X-ray microanalysis of cell nuclei.

The principal component analysis, a multivariate statistical analysis of data, has been used to process X-ray microanalytical data from cell nuclei. Sixty-seven measurements from different areas of chromatin, nucleoli of rat follicular cells, and nucleoli of rat oocyte cells in their antral stage have been studied. The variables are the X-ray characteristic signals for P, S, Al, Fe, Cu, and Zn. This method demonstrates four distinct groups, the chromatin area, which is associated with a higher concentration of P; the compact mass of oocyte nucleolus which possesses the highest content in S, Al, and Zn, and two groups of nucleolar areas. The fibrillar component is richer in S, Al, and Zn than the granular component. The high degree of correlation between these three elements proves the chemical affinity of metals for the proteins (S being the signature for proteins). Cryoembedding in Lowicryl resin at even lower temperatures (213 degrees K in K11M) after quick cryofixation and cryosubstitution in the absence of chemical fixatives gives good ultrastructural preservation and the possibility of simultaneously performing X-ray microanalysis and immunocytochemistry.