Jude Canon

HIV type 1 Gag and nucleocapsid proteins: cytoskeletal localization and effects on cell motility.

Cell motility is likely to play a pivotal role in HIV infection by promoting the dissemination of infected cells. On the basis of observations indicating an interaction between HIV-1 Gag and target cell filamentous actin, we hypothesized that these interactions would promote cell motility of HIV-infected cells. Indeed, we have found that HIV-1 infection enhances the chemotactic response of macrophages. To specifically investigate the significance of the interactions between Gag and cellular actin, we transfected NIH 3T3 fibroblasts and HeLa cells with a construct that permits the expression of HIV-1 Gag in the absence of any other viral protein. Fractionation experiments showed that Gag was present in cytoskeletal fraction containing long actin filaments and in a high-speed postcytoskeletal fraction with short actin filaments. We have also localized HIV-1 Gag to the lamellipodia of chemoattractant-stimulated cells. Significantly, the motility of Gag-expressing cells was enhanced in chemotaxis assays. In vitro mutagenesis experiments showed that HIV-1 Gag binds filamentous actin through the nucleocapsid domain (NC). An NC-green fluorescent protein fusion had the same cellular distribution as the complete protein, and its expression increased cell motility. These data suggest that interactions between HIV-1 Gag and actin in infected cells enhance cell motility. Ultimately this enhanced motility of infected cells could promote the dissemination of virus into the brain and other tissues.

Cell fate specification in the Drosophila eye.

With the passing of the furrow over a uniformly equivalent group of cells, a spectacular array of cell types, each different in structure and function arises in the developing eye disc of Drosophila. A small number of ubiquitously expressed transcription factors combine with an even smaller number of signals emanating from the furrow and the developing clusters and generate cell-specific expression of a panoply of transcription factors (reviewed in Kumar and Moses 1997).The challenge is to understand how the cell-specific transcription factors are placed in their respective cells and how they then function in assigning different identities to each cell type. Here, we have presented our current understanding of this process. The aim is to be eclectic rather than comprehensive, and we apologize in advance to those investigators whose work we have not fully cited.