Amphibian Lens Histones and Their Relation to the Cell Cycle

Histones have been electrophoretically separated from acid extracts of the frog lens for the first time. The five conventional histone fractions, representing four electrophoretic bands (f1; f2b, f3; f2a2; and f2a1), are present in both the epithelial and fiber cells. In addition, a fifth fraction was isolated from both sources and the evidence suggests that it may be a tissue-specific histone, possibly related to the lysine-rich f2c fraction found previously only in nucleated erythrocytes. The epithelial cells contain a substantially greater amount of histone than the fiber cells. Moreover, the fibers, unlike the epithelium, manifest no net histone synthesis or turnover following lenticular explantation. Microspectrophotometric, radioautographic, and gel electrophoretic studies indicate that the histones are synthesized in frog lenses concurrently with DNA. Inhibition of DNA synthesis does not completely abolish that of histones but reduces it by about one-half. In the early stages of culture (prior to their synthesis and that of DNA) the histones appear to undergo alterations which are prevented by treatment with cycloheximide.     

Arabidopsis homolog of the yeast TREX‐2 mRNA export complex: components and anchoring nucleoporin

Nuclear pore complexes (NPCs) are vital to nuclear–cytoplasmic communication in eukaryotes. The yeast NPC‐associated TREX‐2 complex, also known as the Thp1–Sac3–Cdc31–Sus1 complex, is anchored on the NPC via the nucleoporin Nup1, and is essential for mRNA export. Here we report the identification and characterization of the putative Arabidopsis thaliana TREX‐2 complex and its anchoring nucleoporin. Physical and functional evidence support the identification of the Arabidopsis orthologs of yeast Thp1 and Nup1. Of three Arabidopsis homologs of yeast Sac3, two are putative TREX‐2 components, but, surprisingly, none are required for mRNA export as they are in yeast. Physical association of the two Cdc31 homologs, but not the Sus1 homolog, with the TREX‐2 complex was observed. In addition to identification of these TREX‐2 components, direct interactions of the Arabidopsis homolog of DSS1, which is an established proteasome component in yeast and animals, with both the TREX‐2 complex and the proteasome were observed. This suggests the possibility of a link between the two complexes. Thus this work has identified the putative Arabidopsis TREX‐2 complex and provides a foundation for future studies of nuclear export in Arabidopsis.     

The neutrophil response to polyvinyl sponge implantation

Neutrophil release and migration in mice were studied over a 24-hr period after the sc implantation of a single polyvinyl sponge. The release of neutrophils from the marrow was evaluated by directly counting the residual neutrophils in the femoral marrow of animals with sponges. Sponge and tissue neutrophil content was determined by extraction and assay of myeloperoxidase (MPO), a marker enzyme for neutrophils. A maximum depletion of 48% of the mature neutrophils in the marrow was observed 5 hr after sponge implantation, in keeping with significant release of neutrophils for migration to the sponge. The released cells were not found in the circulating granulocyte pool, since neutropenia was noted. The accumulation of neutrophils in the sponge increased throughout the 24-hr period, whereas in the tissue adjacent to the sponge maximum accumulation of neutrophils occurred within 7 hr. In fact, neutrophils migrated to at least three sites--the sponge, the skin overlying the sponge, and the skin in which an incision had been made to insert the sponge. The sponge content of neutrophils represented 0.3-33% of the neutrophils migrating to the combined lesion (sponge and skin sites). Therefore, if the neutrophil response to foreign body implantation is to be measured in its entirety, it is necessary to quantify not only the neutrophils within the foreign body but also those in the tissues surrounding it. These studies describe an animal model for neutrophil release and migration to tissues following a standard stimulus. It is proposed that this model may be useful in exploring the factors which influence the release and migration of neutrophils in vivo.