PCC-like induction of mitosis in Chara vulgaris antheridia initiating differentiation of spermatozoids in the darkness

The objects of this research were the antheridial filament cells of <em>Chara vulgaris</em> which after 5-day mitodepressing treatment of the darkness reactivated mitosis (without light stimulation) in the result of the physiological state evocing the initiation of spermiogenesis in the antheridium. The course of these divisions was observed in relation to control cells cultivated in the natural photoperiod L:D = 14:10. It was shown that the passage of dark-arrested cells from early G₂ (VII stage) to the early prophase in the cells linked to the base of filaments by plasmodesmata with spermatids initiating spermiogenesis, resembles the prematuraly condensed chromosomes (PCC). In this way a by-pass of the cells in the stage VII to early prophase occurs without reconstruction of granular components of nucleoli and with condensed stage of mitochondria characterising the dark-arrested cells. In opposition to this phenomenon in the control cell cycle and in light-induced reactivation of mitosis in the dark-arrested cells, initiation of the prophase follows the series of changes of the nuclear ultrastructure (VIII stage - decondensation of chromatin, IX and X stages nuclei with reticulate chromatin). At the early prophase, irrespective of the physiological conditions, the electron-transparent space appears between nuclear envelope and the chromatin as the effect of solublisation of lamins. The fine fibrils pass this space and link chromatin to the inner nuclear membrane.

Assembly of adenovirus-specific nuclear inclusions in lytically infected HeLa cells: an ultrastructural and cytochemical study

Adenoviruses (Ads) are nuclear DNA viruses that remodel host nuclear structure and function and induce formation of a variety of nuclear inclusions within which Ad DNA is replicated and transcribed. In this study, we have examined inclusion assembly by electron microscopy of samples stained conventionally or with bismuth to detect phosphoproteins. Small dense fibrillar bodies (DFBs) appeared very early associated with interchromatin granule (ICG) clusters. Somewhat later, similar DFBs lay near amorphous, loosely fibrillar structures that were moderately electron dense and showed little bismuth deposition. These clear fibrillar bodies (CFBs) enlarged and DFBs became embedded in their surface. At later stages, CFBs and DFBs were again dissociated. DFBs seen very early were poor in phosphoproteins, but later DFBs, whether embedded in the CFBs or lying near them, were intensely bismuth stained. DFBs and CFBs were less prominent once assembled virions were seen. At this late stage, virions were generally associated with moderately dense, slightly bismuth positive, irregularly shaped fibrillar inclusions that have previously been identified as viral genome storage sites. In addition, very dense fibrillar bodies, consisting usually of an electron-dense fibrillar shell and a less dense fibrogranular core, were observed at all but the earliest stages of infection, often at some distance from CFBs. There was also a major reorganization of host components during infection, including chromatin condensation, reduction of nucleolar volume and aggregation of the fibrillar regions at the nucleolar surface, and increased prominence of ICG clusters. A model is proposed for the assembly of Ad replication factories.Key words: adenovirus, lytic infection, replication factories, nuclear ultrastructure, cytochemistry.