Mitosis in the pinnate diatom surirella ovalis

Abstract

Mitosis in Surirella is described; this organism displays a number of unusual features including an unorthodox method of chromosome attachment to the spindle, and the differentiation of an extranuclear central spindle from a large spherical organelle named the microtubule center (MC). The MC, present during interphase, breaks down at late prophase as the central spindle is formed. Later, the spindle enters the nucleus; the chromatin, in association with microtubules (MTs) from the poles, increasingly aggregates around the middle "overlap" region of the central spindle, and by metaphase completely encircles it. Throughout, MTs usually associate laterally with the chromatin. We were not able to identify kinetochore MTs with confidence at either metaphase or anaphase. Instead, at anaphase the leading point of the chromosomes is embedded in a ring of electrondense material, named the "collar," which encircles each half spindle and extends from the chromatin to the pole. Anaphase separation of the chromosomes is achieved by at least three separate mechanisms: (a) between metaphase and late anaphase the central spindle increases in length by addition of MT subunits; (b) at late anaphase the central spindle elongates concurrent with a reduction in the overlap; this apparently results from an MT/MT sliding mechanism; (c) each set of chromosomes moves to the poles by a thus far unknown mechanism; however, we anticipate some interaction of the collar and central spindle. At telophase, the polar complexes, (i.e., structures at the spindle pole) separate from the spindle, and later a new MC is formed near each polar complex, after which the polar complexes break down. Aspects of the complex differentiation of the MC, spindle formation, and some unusual characteristics of the diatom spindle as they relate to anaphase motion and spindle function are discussed.In 1896, Lauterborn (12) published a detailed account of nuclear and cell division in various diatoms, with emphasis on the pennate diatom Surirella. He noted several unusual features characteristic of mitosis in these organisms, which were not later confirmed by workers using the light microscope (see Discussion). More recently, observed with the electron microscope that the spindle of the centric Lithodesmium does indeed have unusual characteristics. They illustrated in considerable detail the formation of the extranuclear "central spindle" which runs from one pole to the other, and indicated that by metaphase it consists essentially of two halfspindles, each a highly ordered set of microtubules (MTs) which interdigitate in the central "overlap" region. They also demonstrated that the centriole involved in flagellum formation during sexual reThE JOURNAL OF CELL BXOLOGY 9 VOLUlaE 73, 1977 9 pages 705-727 705 on

Localization of kinesin in cultured cells.

“…The only material visible in the electron microscope that correlates with the strong kinesin staining is the amorphous pericentriolar material visible as an osmiophilic matrix. It is possible that the whisps of staining that project into the body of the spindle correspond to the "collar material" seen by Pickett-Heaps and his co-workers in diatoms (33), but analogous structures are not yet documented in other cells.…”

Inhibition of Dendritic Cell Maturation by Malaria Is Dose Dependent and Does Not RequirePlasmodium falciparumErythrocyte Membrane Protein 1

“…A semisimultaneous fixation protocol was used (47). DCs cultured with iRBCs (100 iRBCs per DC) for 4 h were washed in RPMI 1640 medium and then fixed for 5 to 10 seconds with 0.5% glutaraldehyde (ProSciTech) in RPMI 1640 medium; about 10 seconds later, an equal volume of 1% OsO 4 in RPMI 1640 medium was added for 20 min.…”

Post‐mitotic cellular reorganisation in the diatom Cymatopleura solea: The role of microtubules and the microtubule centre

“…Mitosis starts with the spindle arising near the MC (Fig. 11); It is similar to that in Surirellu [Tippit and Pickett-Heaps, 1977;Pickett-Heaps et al, 19841 and will not be described here. At telophase, the new MC in each daughter cell arose close to the spindle pole and enlarged as the latter dispersed (Fig.…”