Meiosis

Cytokinin enhances meiotic cell division in megaspore mother cells of grape (Negi and Olmo 1972). Enhancement of meiosis by cytokinin has also been reported in microspore mother cells of Tradescantia paludosa (Walker and Dietrich 1961). In this case kinetin stimulates the passage of meiotic cells through prophase and, under some conditions, reduces the time between the second meiotic division and the following mitotic division. Prolonged exposure to kinetin, however, causes cessation of meiosis ( meiotic stasis ). 

The effect of ethylene on meiotic chromosomes in microspore mother cells of rye was examined by Boyle and Evans (1974). No information on the effect of ethylene on the timing of the events of meiosis was presented, but the hormone was shown to increase the frequency of chromosomal aberrations. 

Cell division in higher plants requires both cytokinin and auxin. While the cytokinins exhibit the most dramatic effects on cell division they are ineffective in the absence of auxin. The effects of cytokinin and auxin on cell division vary with concentration and with the state of differentiation of the cells. Nondividing differentiated cells are induced to divide when exposed to cytokinin and auxin, while division in rapidly dividing meristematic cells is more likely to be retarded in their presence. This indicates that the control sites for cell cycling may be altered during differentiation, perhaps by a shift in sensitivity to auxins and cytokinins. 

Although there is evidence that hormones play a role in the control of the cell cycle, this control may be indirect, i.e., the hormones may play a permissive role in division or they may influence the cell cycle through effects on expansion or metabolism. It is curious, however, that cells arrested experimentally normally arrest in either or G2 and that gibberellin and cytokinin are important for progression from G to S and G2 to M, respectively. Thus the apparent principal control periods of the cell cycle are those most noticeably responsive to hormones a relationship probably more than coincidental. 

Auxin appears to play more of a permissive role than a site-specific control function in cell division. Cell division requires auxin but transient auxin deprivation shows little or no synchronizing effect on cell proliferation in most cases. Auxin may be necessary for DNA synthesis, but it is clear that auxin acts at one or more points in the cell cycle independently of its effects on DNA synthesis. 

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Ascospore Spores resulting from karyogamy and meiosis that are formed within an ascus. Sexual spore of the Ascomycota. 

The processes of meiosis and mitosis involve many motile events, from the separation of the daughter chromosomes to the final act of cell separation at cytokinesis (Wadsworth, 1993). DNA replication itself may be considered as a motile event, because the polymerase complex moves along the linear DNA. One of the most obvious motile events is the separation of the chromosomes along the mitotic spindle at anaphase. Details of the structure and polarity of microtubules in the spindle apparatus in meiosis and mitosis are known through electron and light microscopy, but it is not yet clear whether the chromosomes are pushed, pulled or... 

Cytokinesis is the separation of daughter cells at the completion of the microtubule directed separation of duplicate chromosomes at mitosis or meiosis. This is usually accomplished by a purse string mechanism, whereby daughter cells become separated by the gradual constriction of a structure composed of actin microfilaments and myosins-II (Fujiwara and Pollard, 1976 Satterwhite and Pollard, 1992). 

Sawin, K.E., Endow, S.A. (1993). Meiosis, mitosis and micrombule motors. BioEssays 15,399-407. 

Mild Tremor, anxiety, insomnia, mood lability, abdominal cramping, nausea, vomiting, palpitations, diaphoresis, tachycardia, meiosis... 

Fig. 2.6 The moqjhological events of sporulation in Saccharomyces cerevisiae. (a) starved cell V, vacuole LG, lipid granule ER, endoplasmic reticulum CW, cell wall M, mitochondrion S, spindle pole SM, spindle microtubules N, nucleus NO, nucleolus, (b) Synaptonemal complex (SX) and development of polycomplex body (PB) along with division of spindle pole body in (c). (d) First meiotic division which is completed in (e). (f) Prepararation for meiosis II. (g) Enlargement of prospore wall, culminating in enclosure of separate haploid nuclei (h). (i) Spore coat (SC) materials produced and deposited, giving rise to the distinct outer spore coat (OSC) seen in the completed spores of the mature ascus (j). Reproduced from the review by Dickinson (1988) with permission from Blackwell Science Ltd.

Courtot, C., Fankhauser, C., Simanis, V., and Lehner, C. F. (1992). The Drosophila cdc25 homolog twine is required for meiosis. Development 116 405-416. 

Grandin, N., and Reed, S. I. (1993). Differential function and expression of Saccharomy-ces cerevisiae B-type cyclins in mitosis and meiosis. Mol. Cell. Biol. 13 2113— 2125. 

Kanki, J. P, and Donoghue, D. J. (1991). Progression from meiosis I to meiosis II in Xenopus oocytes requires de novo translation of the mos" protooncogene. Proc. Natl. Acad. Sci. USASS 5794-5798. 

Matsushime, H Jinno, A., Takagi, N and Shibuya, M. (1990). A novel mammalian protein kinase gene (mak) is highly expressed in testicular germ cells at and after meiosis. Mol. Cell. Biol. 10 2261-2268. 

O Keefe, S. J., Wolfes, H., Kiessling, A. A., and Cooper, G. M. (1989). Microinjection of antisense c-mos oligonucleotides prevents meiosis II in maturing mouse eggs. Proc. Natl. Acad. Sci. USA 86 7038-7042. 

Posada, J., and Cooper, J. A. (1992). Requirements for phosphorylation of MAP kinase during meiosis in Xenopus oocytes. Science 255 212-215. 

Swenson, K. I., Farrell, K. M., and Ruderman, J. V. (1986). The clam embryo protein cyclin A induces entry into M phase and the resumption of meiosis in Xenopus oocytes. Cell 47 861-870. 

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