The nuclear matrix of Euglena gracilis (Euglenophyta): A stage of nuclear matrix evolution?

Euglena gracilis cell was extracted sequentially with CSK-Triton buffer, RS B-Magik solution and DNase-As solution. DGD embedment-free electron microsc opy showed that in the extracted nucleus there was a residual non-chromatin fibrous network. That it could not be removed by hot trichloroacetic acid further supported the idea that it was a non-histone, non-chromatin fibrous protein network, and should be the internal network of the nuclear matrix. After the sequential extraction, the nuclear membrane was removed, leaving behind a layer of lamina; the chromatin was digested and eluted from the d ense chromosomes and residual chromosomal structures that should be chromos omal scaffold were revealed. Western blot analysis with antiserum against r at lamins showed that nuclear lamina of the cell possessed two positive pol ypeptides, a major one and a minor one, which had molecular masses similar to lamin B and lamin A, respectively. Comparing these data with those of th e most primitive eukaryote Archezoa and of higher eukaryotes, it was sugges ted that the lower unicellular eukaryote E. gracillis already had the nucle ar matrix structure, and its nuclear matrix (especially the lamina) might r epresent a stage of evolutionary history of the nuclear matrix. (C) 2000 Ed itions scientifiques et medicales Elsevier SAS.