Future Daughter Cells Research Articles

Rab35 Regulates an Endocytic Recycling Pathway Essential for the Terminal Steps of Cytokinesis

Cytokinesis is the final step of cell division and leads to the physical separation of the daughter cells. After the ingression of a cleavage membrane furrow that pinches the mother cell, future daughter cells spend much of the cytokinesis phase connected by an intercellular bridge. Rab proteins are major regulators of intracellular transport in eukaryotes, and here, we report an essential role for human Rab35 in both the stability of the bridge and its final abscission. We find that Rab35, whose function in membrane traffic was unknown, is localized to the plasma membrane and endocytic compartments and controls a fast endocytic recycling pathway. Consistent with a key requirement for Rab35-regulated recycling during cell division, inhibition of Rab35 function leads to the accumulation of endocytic markers on numerous cytoplasmic vacuoles in cells that failed cytokinesis. Moreover, Rab35 is involved in the intercellular bridge localization of two molecules essential for the postfurrowing steps of cytokinesis: the phosphatidylinositol 4,5-bis phosphate (PIP2) lipid and the septin SEPT2. We propose that the Rab35-regulated pathway plays an essential role during the terminal steps of cytokinesis by controlling septin and PIP2 subcellular distribution during cell division.

Altered morphology produced by ftsZ expression in Corynebacterium glutamicum ATCC 13869

Corynebacterium glutamicum is a Gram-positive bacterium that lacks the cell division FtsA protein and actin-like MreB proteins responsible for determining cylindrical cell shape. When the cell division ftsZ gene from C. glutamicum (ftsZ(Cg)) was cloned in different multicopy plasmids, the resulting constructions could not be introduced into C. glutamicum; it was assumed that elevated levels of FtsZ(Cg) result in lethality. The presence of a truncated ftsZ(Cg) and a complete ftsZ(Cg) under the control of Plac led to a fourfold reduction in the intracellular levels of FtsZ, generating aberrant cells displaying buds, branches and knots, but no filaments. A 20-fold reduction of the FtsZ level by transformation with a plasmid carrying the Escherichia coli lacI gene dramatically reduced the growth rate of C. glutamicum, and the cells were larger and club-shaped. Immunofluorescence microscopy of FtsZ(Cg) or visualization of FtsZ(Cg)-GFP in C. glutamicum revealed that most cells showed one fluorescent band, most likely a ring, at the mid-cell, and some cells showed two fluorescent bands (septa of future daughter cells). When FtsZ(Cg)-GFP was expressed from Plac, FtsZ rings at mid-cell, or spirals, were also clearly visible in the aberrant cells; however, this morphology was not entirely due to GFP but also to the reduced levels of FtsZ expressed from Plac. Localization of FtsZ at the septum is not negatively regulated by the nucleoid, and therefore the well-known occlusion mechanism seems not to operate in C. glutamicum.

Xenopus polo-like kinase Plx1 regulates XErp1, a novel inhibitor of APC/C activity

Metaphase-to-anaphase transition is a fundamental step in cell cycle progression where duplicated sister-chromatids segregate to the future daughter cells. The anaphase-promoting complex/cyclosome (APC/C) is a highly regulated ubiquitin-ligase that triggers anaphase onset and mitotic exit by targeting securin and mitotic cyclins for destruction. It was previously shown that the Xenopus polo-like kinase Plx1 is essential to activate APC/C upon release from cytostatic factor (CSF) arrest in Xenopus egg extract. Although the mechanism by which Plx1 regulates APC/C activation remained unclear, the existence of a putative APC/C inhibitor was postulated whose activity would be neutralized by Plx1 upon CSF release. Here we identify XErp1, a novel Plx1-regulated inhibitor of APC/C activity, and we demonstrate that XErp1 is required to prevent anaphase onset in CSF-arrested Xenopus egg extract. Inactivation of XErp1 leads to premature APC/C activation. Conversely, addition of excess XErp1 to Xenopus egg extract prevents APC/C activation. Plx1 phosphorylates XErp1 in vitro at a site that targets XErp1 for degradation upon CSF release. Thus, our data lead to a model of APC/C activation in Xenopus egg extract in which Plx1 targets the APC/C inhibitor XErp1 for degradation.

The metaphase to anaphase transition: a case of productive destruction.

The metaphase to anaphase transition is a point of no return; the duplicated sister chromatids segregate to the future daughter cells, and any mistake in this process may be deleterious to both progeny. At the heart of this process lies the anaphase inhibitor, which must be degraded in order for this transition to take place. The degradation of the anaphase inhibitor occurs via the ubiquitin-degradation pathway, and it involves the activity of the cyclosome/anaphase promoting complex (APC). The fidelity of the metaphase to anaphase transition is ensured by several different regulatory mechanisms that modulate the activity of the cyclosome/APC. Great advancements have been made in this field in the past few years, but many questions still remain to be answered.

Transformation of the flagella and associated flagellar components during cell division in the coccolithophoridPleurochrysis carterae

Immunofluorescence microscopy, conventional and high voltage transmission electron microscopy were used to describe changes in the flagellar apparatus during cell division in the motile, coccolithbearing cells ofPleurochrysis carterae (Braarud and Fagerlund) Christensen. New basal bodies appear alongside the parental basal bodies before mitosis and at prophase the large microtubular (crystalline) roots disassemble as their component microtubules migrate to the future spindle poles. By prometaphase the crystalline roots have disappeared; the flagellar axonemes shorten and the two pairs of basal bodies (each consisting of one parental and one daughter basal body) separate so that each pair is distal to a spindle pole. By late prometaphase the pairs of basal bodies bear diminutive flagellar roots for the future daughter cells. The long flagellum of each daughter cell is derived from the parental basal bodies; thus, the basal body that produces a short flagellum in the parent produces a long flagellum in the daughter cell. We conclude that each basal body in these cells is inherently identical but that a first generation basal body generates a short flagellum and in succeeding generations it produces a long flagellum. At metaphase a fibrous band connecting the basal bodies appears and the roots and basal bodies reorient to their interphase configuration. By telophase the crystalline roots have begun to reform and the rootlet microtubules have assumed their interphase appearance by early cytokinesis.

Asymmetric division of lymphoid cells of the embryonic chicken thymus. An ultrastructural study with the use of serial sectioning method

Our previous observations on smeared cells of the embryonic chicken thymus revealed that some lymphoid cells displayed features implicating asymmetric cell division [1]. In this paper, in situ division of 11-day embryonic chicken lymphoid cells was studied ultrastructurally with the use of serial sections of the thymus. Asymmetrically dividing lymphoid cells were found: one of the two future daughter cells at telophase alone possessed a large organelle-free hyaline process and its cytoplasm was apparently greater in amount than that of the counterpart. On the basis of these results, it has been concluded that some lymphoid cells in the thymus of embryonic chickens would undergo in sity asymmetric cell division to generate progenitor cells which are heterogeneous in terms of morphological criteria.

DEVELOPMENT OF THE EMBRYONIC CHICKEN THYMUS III. UNEQUAL DIVISION OF LYMPHOID CELLS.

Cell division of thymus lymphoid cells from 11- to 17-day old embryonic chickens, as well as chickens just after hatch was investigated on cell smears stained with Giemsa. Unequally dividing cells were observed in the developmental stage of thymocytes. At the telophase of such cells, the cytoplasm of one of two future daughter cells was apparently larger in amount and was sometimes stained deeper than the cytoplasm of its counterpart. Unequal division was also observed in pro-, meta- and anaphase; sometimes a dividing cell had a large cytoplasmic process belonging to one hemisphere, suggesting that only one of the two daughter cells would receive the cytoplasmic process through cell division. The incidence of unequal division calculated by a rough estimation was around 10% of the total cell division between 11 and 13 days of embryonic development, and decreased progressively thereafter.