Differential dynamics of splicing factor SC35 during the cell cycle.

Pre-mRNA splicing factors are enriched in nuclear domains termed interchromatin granule clusters or nuclear speckles. During mitosis, nuclear speckles are disassembled by metaphase and reassembled in telophase in structures termed mitotic interchromatin granules (MIGs). We analysed the dynamics of the splicing factor SC35 in interphase and mitotic cells. In HeLa cells expressing green fluorescent protein (GFP)-SC35, this was localized in speckles during interphase and dispersed in metaphase. In telophase, GFP-SC35 was highly enriched within telophase nuclei and also detected in MIGs. Fluorescence recovery after photobleaching (FRAP) experiments revealed that the mobility of GFP-SC35 was distinct in different mitotic compartments. Interestingly, the mobility of GFP-SC35 was 3-fold higher in the cytoplasm of metaphase cells compared with interphase speckles, the nucleoplasm or MIGs. Treatment of cells with inhibitors of cyclin-dependent kinases (cdks) caused changes in the organization of nuclear compartments such as nuclear speckles and nucleoli, with corresponding changes in the mobility of GFP-SC35 and GFP-fibrillarin. Our results suggest that the dynamics of SC35 are significantly influenced by the organization of the compartment in which it is localized during the cell cycle.

Dibutyryl c-AMP as an inducer of sporidia formation: biochemical and antigenic changes during morphological differentiation of Karnal bunt (Tilletia indica) pathogen in axenic culture.

Effect of dibutyryl adenosine 3',5'-cyclic monophosphate (dbc-AMP), an analogue of c-AMP, was investigated on growth and morphological differentiation of Tilletia indica. Exponential growth was observed up to 21 days in both presence and absence of dbc-AMP; however, increasing concentration of dbc-AMP was deleterious to mycelial growth in liquid culture. A slow increase of mycelial biomass up to 21 days and decline at 30 days in the presence of 2.5 mM dbc-AMP was observed, therefore, this concentration was chosen in subsequent investigations. The inhibitory influence of dbc-AMP was further substantiated by decrease in soluble protein. The fungus on exposure to dbc-AMP experienced morphological differentiation from vegetative mycelial phase to sporogenous mycelial phase, and was induced to produce filiform sporidia. Use of quantitative ELISA further suggested that sporidia formation took more than 21 days in the presence of dbc-AMP. Variations of proteins during different stages of T. indica grown in the presence and absence of dbc-AMP suggested the expression of stage-specific proteins or differential expression of proteins induced by dbc-AMP. The changes in expression of cell surface antigens as evidenced from decrease and increase binding of anti-mycelial and anti-sporidial antibodies in dbc-AMP treated culture by ELISA was further interpreted on the basis of morphological differentiation from mycelial to sporidial phase