Waheeb K. Heneen

In situ analysis of normal and abnormal patterns of the mitotic apparatus in cultured rat-kangaroo cells

Dividing cells in monolayers of the rat-kangaroo (Potorous tridactylis) cell line Pt-K1 have large spindles and are flat, thus making possible studies of interactions between the achromatic and chromatic parts of the mitotic apparatus during the cell cycle. At prophase, asters and centrioles seem to exert pressure on the nuclear membrane leading to its rupture and penetrance of the centrioles. Apparently, the long axis of the spindle is shorter than the nuclear diameter. What appears as persistent, large portions of the nuclear membrane were observed in some metaphase and anaphase cells. Such a condition might also indicate an arrested mitosis. The midbody, which was often bipartite, was found to be of a ribonucleoprotein nature. — Three-group metaphases were of common occurrence and might represent early stages of chromosome orientation preceding the final alignment of the chromosomes on the equatorial plate. They could also be an expression of an anomalous condition as a result of mitotic arrest during prometaphase owing to spindle inactivation or breakage, errors in centromere-spindle attachments, interference with chromosome movement, or a duplicated centriolar constitution. Most of these aberrations could be attributed to the flatness of dividing cells, which might also bring about the failure of centriole separation and spindle organization in prometaphase stages, as well as multipolar mitosis.De novo organization of half spindles might take place in cells with ruptured spindles. Anaphase cells showing signs of a previous three-group orientation were rare. — Multipolar mitoses were prevalent mainly in cells with high chromosome numbers. They were often star-shaped with the chromosomes oriented between opposite and adjacent poles, and rarely as end-to-end associations of spindles. Apparently, one or more centrioles might share a common polar region. Multipolar configurations have either a mono- or multinuclear origin. Nuclei usually enter division synchronously in binucleate cells and the spindles become organized between centrioles associated with individual or different nuclei.

Silver staining of nucleolar organizers and nucleoli during mitosis and interphase of mammalian cells

The silver staining method Ag-I was applied on metaphase spreads and monolayers of rat-kangaroo (Pt-K1), Indian muntjac, human diploid (F2000) and HeLa-derivative (Lul06) cells. This made discernible the sites of active nucleolar organizers or ribosomal DNA in chromosomes during mitosis and in nuclei during interphase. The numbers and relative sizes of Ag-stainable materials were consistent when comparing patterns observed at metaphase with those of later mitotic stages and of early interphase nuclei. The Ag-stainable material in the metaphase chromosomes is thus nucleolar in nature. Additional faintly Ag-stainable materials, probably persistent nucleoli, frequently occurred in the cytoplasm of dividing cells especially at anaphase and telophase stages. During advanced stages of interphase, the nucleoli were differentiable into beaded chain-like Ag-positive structures embedded in a brownish homogenous background. These two types of structures are most probably analogous to the nucleolonemata and pars amorpha demonstrable at the light microscopial level, and to the fibrillar and granular components at the ultrastructural level. The appearance of the beaded structures might be related to the activity of the repetitive ribosomal genes. Thus a chain-like organization would be an expression of rDNA redundancy both at the structural and functional level.

Morphology of Human Cells, Carrier of Measles Virus, Using Nomarski Optics and Scanning Electron Microscopy

SummaryA human cell line (Lu106) carrier of measles virus was studied in a Nomarski interference-contrast microscope (NICM) and a scanning electron microscope (SEM). The results from this were correlated with fine structure findings obtained from analyses made in the transmission electron microscope (TEM). In both the NICM and SEM it was possible to identify intracellular perinuclear structures, which most likely represent aggregates of measles nucleocapsids. These structures appeared in the NICM as opaque vesicles and in the SEM as bulges in the flattened cells. The SEM also proved to be useful for determining cell surface characteristics specific for the carrier culture, which were lacking in uninfected Lul06 cells. In the carrier culture, there were vesiculated cells with bleb-like polymorphic and ridged projections, and cells with webbed cytoplasmic extensions. Ridges and transverse striations observed on these cellular protrusions and on microvilli possibly denote oriented viral nucleocapsids at the cell membrane. Furthermore in the carrier cells, the microvilli were more heterogenous in length and diameter and were more frequently branched or fused together when compared to microvilli in uninfected cells. The results are discussed in view of the available information on the appearance of virus-infected or virus-transformed cells in the SEM, also in regard to the various factors, other than virus infection, which play a role in determining the surface features of monolayer cells.