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Involvement of cytoskeleton in orientation of cell division in contact guided cells

100%

Krzysiek-Maczka G. , Michalik M. , Madeja Z. , Korohoda W.

nr 1-2

21-27

Single human skin fibroblasts and the skin keratinocyte cell line HaCaT show contact guidance and elongate along narrow (1-2 Fm) scratches in glass substratum. During cell division these cells orientate their mitotic spindles along the long axis of the cell. Immunofluorescence staining of actin, tubulin, chromatin, and the nuclear NuMA protein complex demonstrated that cell elongation along scratches is accompanied by a corresponding rearrangement in the cytoskeleton. The results and literature suggest the following steps in the interplay between outside-in and inside-out signalling in the regulation of cell division orientation by extracellular factors. The interaction of cell surface with an anisotropy in the local environment causes changes in F-actin organization, cell elongation and alignment of stress fibres along the cell axis. This is accompanied by a corresponding reorientation of microtubules. Microtubules mediate between cell shape changes dependent upon cell interaction with substratum or other cells, the cortical actin and the position of centrosomes. Centrosomes determine the position and orientation of the mitotic spindle. The astral and central microtubules of the mitotic spindle control the localization of contraction-relaxation in the cell cortex and the position of the constriction ring and cell division plane.

Predetermination of cytokinesis and transition from holoblastic to partial superficial cleavage in early embryonic development of Tetrodontophora bielanensis (Collembola)

88%

Klag J. , Krzysztofowicz A. , Jura C. , Kisiel E.

nr 3-4

137-142

In the T. bielanensis embryo, only karyokinesis occurs during the first cleavage division, and a two-nuclear syncytial embryo forms. Then, two cytoplasmic concentrations in the form of elongated rolls perpendicular to each other develop below the periplasm at the animal pole of the egg. The second cleavage division is also associated with karyokineses only. After the embryo reaches the four-nuclear stage, cytokineses occur at its animal pole, and two cleavage furrows perpendicular to each other develop in the periplasm above the cytoplasmic concentrations. The cell membranes forming within the furrows do not invade the cytoplasmic concentrations, but their growing tips push them into the egg interior, where they merge and form the central cytoplasmic concentration. The developing cell membranes do not invade the central cytoplasm; they band and grow above its surface. Four pyramidal blastomeres form as a result of this. The eight-blastomere embryo forms through both karyokinesis and cytokinesis, but the growing cell membranes now band below the previous ones and cut off anucleate parts of the mother blastomeres, which fuse with the central cytoplasm. Thus, during this phase of development the transition from holoblastic to partial superficial cleavage is initiated. Morphological analysis suggests that the formation of the first two cytokineses is predetermined by and depends on factors connected with the animal pole periplasm. It also suggests that the central cytoplasm constitutes the morphological field, inducing the transition from holoblastic to partial superficial cleavage.