scholarly journals Key events during the transition from rapid growth to quiescence in budding yeast require posttranscriptional regulators

2013 ◽  
Vol 24 (23) ◽  
pp. 3697-3709 ◽  
Author(s):  
Lihong Li ◽  
Shawna Miles ◽  
Zephan Melville ◽  
Amalthiya Prasad ◽  
Graham Bradley ◽  
...  
Keyword(s):  
Cell Walls ◽  
Posttranscriptional Regulation ◽  
Cell Formation ◽  
Cell Types ◽  
G1 Arrest ◽  
Quiescent State ◽  
Diauxic Shift ◽  
Cell Wall Assembly ◽  
Daughter Cells ◽  
Mother Cells

Yeast that naturally exhaust the glucose from their environment differentiate into three distinct cell types distinguishable by flow cytometry. Among these is a quiescent (Q) population, which is so named because of its uniform but readily reversed G1 arrest, its fortified cell walls, heat tolerance, and longevity. Daughter cells predominate in Q-cell populations and are the longest lived. The events that differentiate Q cells from nonquiescent (nonQ) cells are initiated within hours of the diauxic shift, when cells have scavenged all the glucose from the media. These include highly asymmetric cell divisions, which give rise to very small daughter cells. These daughters modify their cell walls by Sed1- and Ecm33-dependent and dithiothreitol-sensitive mechanisms that enhance Q-cell thermotolerance. Ssd1 speeds Q-cell wall assembly and enables mother cells to enter this state. Ssd1 and the related mRNA-binding protein Mpt5 play critical overlapping roles in Q-cell formation and longevity. These proteins deliver mRNAs to P-bodies, and at least one P-body component, Lsm1, also plays a unique role in Q-cell longevity. Cells lacking Lsm1 and Ssd1 or Mpt5 lose viability under these conditions and fail to enter the quiescent state. We conclude that posttranscriptional regulation of mRNAs plays a crucial role in the transition in and out of quiescence.

scholarly journals The Culture and Correlative Electron Microscopy of Pollen Mother Cells in Meiosis: Development of Techniques and Some Observations on Selected Topics

2021 ◽  
Author(s):  
◽  
Kenneth George Ryan
Keyword(s):  
Electron Microscopy ◽  
Light And Electron Microscopy ◽  
Cell Formation ◽  
Cell Types ◽  
Future Research ◽  
Thin Sections ◽  
Pollen Mother Cells ◽  
Spindle Elongation ◽  
Mother Cells ◽  
Metaphase I

<p>Reliable techniques for the living cell culture and correlative light and electron microscopy (EM) of meiotic pollen mother cells (PMCs) of Iris spuria, Allium triquetrum and Tradescantia flumenensis are described in detail. Living PMCs were successfully cultured in a slide chamber on agar/sucrose medium. Cells were covered with an inert oil to prevent their dehydration, and some cells were cultured from metaphase I to tetrad cell formation over a 20 hour period. Other PMCs were fixed with glutaraldehyde and flat embedded using a modification of the agar sandwich technique of Mole-Bajer and Bajer (1968). This technique was developed to permit the preselection of PMCs at known meiotic stages, for subsequent EM examination. Serial thin sections were cut at known planes of section; and 3-D reconstructions of MT distribution, and MT counts from transverse sections were completed. It was also possible to examine sections of an Iris anaphase I PMC which had been previously studied in life. Anaphase I and II chromosome velocities were analysed in the three species. Mean velocities were approximately 0.5 mu m/min with some variation from cell to cell and between sister half-spindles. In Allium anaphase I there was also variation in chromosome velocity within the half-spindle; and this variation was found not to be related to chromosome position on the metaphase I plate. Spindle elongation was zero in Allium anaphase I and in Iris anaphase II, but was detectable in Allium anaphase II (40%) and in "Iris anaphase I (l5%). The extent of spindle elongation in Tradescantia could not be determined. The kinetochore region in the first meiotic division consisted of two closely appressed, but structurally (and functionally) distinct, sister kinetochores. At meiosis II, the two sister kinetochores were separate from each other and faced opposite poles. The kinetochore arrangement probably changes from side-by-side (meiosis I) to back-to-back (meiosis II) during chromosome recondensation at prophase II in these cells. Bundles of non-kinetochore microtubules (nkMTs) span the interzone between sister chromosome units at metaphase I and II and anaphase II. Bundles of kinetochore MTs (kMTs) do not increase in divergence at any stage of meiosis studied; there was little interaction between nkMTs and kMTs, and MT-MT cross bridges were rare. These observations are not consistent with models of chromosome movement based on MT sliding or zipping. No relationship was found between nkMT distribution and spindle elongation, and the several different nkMT distributions which have been reported for other cell types may be variations on a structural theme. Spindle endoplasmic reticulum (ER) in meiosis II was found to be derived largely from invaginations and evaginations of the nuclear envelope. Growth of existing spindle ER was proposed to account for the doubling in the amount of ER observed between interphase and prometaphase II. Randomly oriented elements of ER, in early prometaphase II spindles may become passively aligned along the interpolar axis and then actively transported polewards at later stages of prometaphase II and metaphase II. Suggestions for future research are offered.</p>

scholarly journals The MAP She1 coordinates directional spindle positioning by spatially restricting dynein activity

2021 ◽  
Author(s):  
Kari H. Ecklund ◽  
Megan E. Bailey ◽  
Carsten K. Dietvorst ◽  
Charles L. Asbury ◽  
Steven M. Markus
Keyword(s):  
Daughter Cell ◽  
Cell Types ◽  
Division Plane ◽  
Spindle Positioning ◽  
Daughter Cells ◽  
Anaphase Onset ◽  
Microtubule Binding Domain ◽  
Mother And Daughter ◽  
Mother Cells ◽  
Cell Division Plane

ABSTRACTDynein motors move the mitotic spindle to the cell division plane in many cell types, including in budding yeast, in which dynein is assisted by numerous factors including the microtubule-associated protein (MAP) She1. Evidence suggests that She1 plays a role in polarizing dynein-mediated spindle movements toward the daughter cell; however, how She1 performs this function is unknown. We find that She1 assists dynein in maintaining the spindle close to the bud neck, such that at anaphase onset the chromosomes are segregated to mother and daughter cells. She1 does so by attenuating the initiation of dynein-mediated spindle movements specifically within the mother cell, ensuring such movements are polarized toward the daughter cell. Our data indicate that this activity relies on She1 binding to the microtubule-bound conformation of the dynein microtubule-binding domain, and to astral microtubules within mother cells. Our findings reveal how an asymmetrically localized MAP directionally tunes dynein activity by attenuating motor activity in a spatially confined manner.

scholarly journals Posttranscriptional Regulation of HO Expression by the Mkt1-Pbp1 Complex

2004 ◽  
Vol 24 (9) ◽  
pp. 3670-3681 ◽  
Author(s):  
Tomofumi Tadauchi ◽  
Toshifumi Inada ◽  
Kunihiro Matsumoto ◽  
Kenji Irie
Keyword(s):  
Posttranscriptional Regulation ◽  
Untranslated Region ◽  
Mrna Levels ◽  
Mating Types ◽  
Protein Loss ◽  
Protein Levels ◽  
Daughter Cells ◽  
Mother And Daughter ◽  
Mother Cells ◽  
Posttranscriptional Level

ABSTRACT Cells of budding yeast give rise to mother and daughter cells, which differ in that only mother cells express the HO endonuclease gene and are thereby able to switch mating types. In this study, we identified the MKT1 gene as a positive regulator of HO expression. The MKT1 gene encodes a protein with two domains, XPG-N and XPG-I, which are conserved among a family of nucleases, including human XPG endonuclease. Loss of MKT1 had little effect on HO mRNA levels but resulted in decreased protein levels. This decrease was dependent on the 3′ untranslated region of the HO transcript. We screened for proteins that associate with Mkt1 and isolated Pbp1, a protein that is known to associate with Pab1, a poly(A)-binding protein. Loss of PBP1 resembles an mkt1Δ deletion, causing decreased expression of HO at the posttranscriptional level. Mkt1 and Pbp1 cosedimented with polysomes in sucrose gradients, with Mkt1 distribution in the polysomes dependent on Pbp1, but not vice versa. These observations suggest that a complex of Mkt1 and Pbp1 regulates the translation of HO mRNA.

Protoplast isolation from Ulmusamericana L. pollen mother cells, tetrads, and microspores

1980 ◽  
Vol 10 (3) ◽  
pp. 284-289 ◽  
Author(s):  
M. K. Redenbaugh ◽  
R. D. Westfall ◽  
D. F. Karnosky
Keyword(s):  
Cell Division ◽  
Protoplast Fusion ◽  
Cell Walls ◽  
Cell Types ◽  
Protoplast Isolation ◽  
Important Condition ◽  
Pollen Mother Cells ◽  
Regenerate Cell ◽  
Mother Cells ◽  
Induce Cell Division

Meiotic protoplasts of Ulmusamericana (American elm) are potentially valuable for producing interspecific elm hybrids through protoplast fusion. Meiotic cells (pollen mother cells, tetrads, and microspores) were incubated in either a cellulase, hemicellulase, and pectinase enzyme solution or a β-1,3-glucanase (laminarinase) solution. Respective protoplast isolation frequencies for the three meiotic cell types were 100, 50, and 10%. Exclusion staining with 0.2% Evans blue and 0.1% methyl blue suggested protoplast viability. Some of the microspore protoplasts were vacuolated, which is an important condition for cell division. Although attempts to regenerate cell walls and induce cell division were unsuccessful, these two problems may be superceded by protoplast fusion with more regenerative protoplasts. To our knowledge this is the first report of protoplast isolation from meiotic cells of a tree species.

scholarly journals The MAP She1 coordinates directional spindle positioning by spatially restricting dynein activity

2021 ◽  
Author(s):  
Kari H. Ecklund ◽  
Megan E. Bailey ◽  
Kelly A. Kossen ◽  
Carsten K. Dietvorst ◽  
Charles L. Asbury ◽  
...  
Keyword(s):  
Daughter Cell ◽  
Cell Types ◽  
Division Plane ◽  
Spindle Positioning ◽  
Daughter Cells ◽  
Anaphase Onset ◽  
Microtubule Binding Domain ◽  
Close Proximity ◽  
Mother And Daughter ◽  
Mother Cells

Dynein motors move the mitotic spindle to the cell division plane in many cell types, including in budding yeast, in which dynein is assisted by numerous factors including the microtubule-associated protein (MAP) She1. Evidence suggests that She1 plays a role in polarizing dynein-mediated spindle movements toward the daughter cell; however, how She1 performs this function is unknown. We find that She1 assists dynein in maintaining the spindle in close proximity to the bud neck, such that at anaphase onset the chromosomes are segregated to mother and daughter cells. She1 does so by attenuating the initiation of dynein-mediated spindle movements within the mother cell, thus ensuring such movements are polarized toward the daughter cell. Our data indicate that this activity relies on She1 binding to the microtubule-bound conformation of the dynein microtubule-binding domain, and to astral microtubules within mother cells. Our findings reveal how an asymmetrically localized MAP directionally tunes dynein activity by attenuating motor activity in a spatially confined manner.

scholarly journals The Culture and Correlative Electron Microscopy of Pollen Mother Cells in Meiosis: Development of Techniques and Some Observations on Selected Topics

2021 ◽  
Author(s):  
◽  
Kenneth George Ryan
Keyword(s):  
Electron Microscopy ◽  
Light And Electron Microscopy ◽  
Cell Formation ◽  
Cell Types ◽  
Future Research ◽  
Thin Sections ◽  
Pollen Mother Cells ◽  
Spindle Elongation ◽  
Mother Cells ◽  
Metaphase I

<p>Reliable techniques for the living cell culture and correlative light and electron microscopy (EM) of meiotic pollen mother cells (PMCs) of Iris spuria, Allium triquetrum and Tradescantia flumenensis are described in detail. Living PMCs were successfully cultured in a slide chamber on agar/sucrose medium. Cells were covered with an inert oil to prevent their dehydration, and some cells were cultured from metaphase I to tetrad cell formation over a 20 hour period. Other PMCs were fixed with glutaraldehyde and flat embedded using a modification of the agar sandwich technique of Mole-Bajer and Bajer (1968). This technique was developed to permit the preselection of PMCs at known meiotic stages, for subsequent EM examination. Serial thin sections were cut at known planes of section; and 3-D reconstructions of MT distribution, and MT counts from transverse sections were completed. It was also possible to examine sections of an Iris anaphase I PMC which had been previously studied in life. Anaphase I and II chromosome velocities were analysed in the three species. Mean velocities were approximately 0.5 mu m/min with some variation from cell to cell and between sister half-spindles. In Allium anaphase I there was also variation in chromosome velocity within the half-spindle; and this variation was found not to be related to chromosome position on the metaphase I plate. Spindle elongation was zero in Allium anaphase I and in Iris anaphase II, but was detectable in Allium anaphase II (40%) and in "Iris anaphase I (l5%). The extent of spindle elongation in Tradescantia could not be determined. The kinetochore region in the first meiotic division consisted of two closely appressed, but structurally (and functionally) distinct, sister kinetochores. At meiosis II, the two sister kinetochores were separate from each other and faced opposite poles. The kinetochore arrangement probably changes from side-by-side (meiosis I) to back-to-back (meiosis II) during chromosome recondensation at prophase II in these cells. Bundles of non-kinetochore microtubules (nkMTs) span the interzone between sister chromosome units at metaphase I and II and anaphase II. Bundles of kinetochore MTs (kMTs) do not increase in divergence at any stage of meiosis studied; there was little interaction between nkMTs and kMTs, and MT-MT cross bridges were rare. These observations are not consistent with models of chromosome movement based on MT sliding or zipping. No relationship was found between nkMT distribution and spindle elongation, and the several different nkMT distributions which have been reported for other cell types may be variations on a structural theme. Spindle endoplasmic reticulum (ER) in meiosis II was found to be derived largely from invaginations and evaginations of the nuclear envelope. Growth of existing spindle ER was proposed to account for the doubling in the amount of ER observed between interphase and prometaphase II. Randomly oriented elements of ER, in early prometaphase II spindles may become passively aligned along the interpolar axis and then actively transported polewards at later stages of prometaphase II and metaphase II. Suggestions for future research are offered.</p>

Interpolation of microtubules into cortical arrays during cell elongation and differentiation in roots of Azolla pinnata

1979 ◽  
Vol 37 (1) ◽  
pp. 411-442
Author(s):  
A.R. Hardham ◽  
B.E. Gunning
Keyword(s):  
Cell Differentiation ◽  
Cell Walls ◽  
Unit Length ◽  
Cell Types ◽  
High Rate ◽  
Wall Thickening ◽  
Cortical Microtubules ◽  
Azolla Pinnata ◽  
Outer Cortex ◽  
Cortical Cells

Longitudinal sections of roots of Azolla pinnata R. Br. were prepared for electron microscopy so that cortical microtubules could be counted along the longitudinal walls in cell files in the endodermis, pericycle, and inner and outer cortex, and in sieve and xylem elements. With the exception of the xylem, where there are no transverse cell divisions, each file of cells commences with its initial cell and then possesses a zone of concomitant cell expansion and transverse cell division, followed, after completion of the divisions, by a zone of terminal cell differentiation. The cells augment their population of cortical microtubules as they elongate and divide, showing a net increase of up to 0.6 micron of polymerized microtubule length per min. Two main sub-processes were found: (i) When a longitudinal wall is first formed it is supplied with a higher number of microtubules per unit length of wall than it will have later, when it is being expanded. This initial quota becomes diluted as the second sub-process commences. (ii) The cells interpolate new microtubules at a rate which is characteristic of the cell, and, in the endodermis, of the face of the cell, while the cell elongates. Most cell types thus maintain a set density of cortical microtubules while they elongate and divide. Comparisons of endodermal cells in untreated controls, and roots that had been treated with colchicine, low temperature, or high pressure indicate that the initial quota of microtubules, and the later interpolations, and differentially sensitive to microtuble perturbations. Three types of behaviour, all related to changes in the cell walls, were noted as cortex, xylem and sieve element cells entered their respective phases of cell differentiation. The cortical cells expanded in all dimensions, and the interpolation of microtubules diminished or ceased. The sieve elements continued to elongate, and interpolated at a high rate, reaching unusually high densities of microtubules when the cell walls were being thickened. During this period a net increase of 2.0 micron of polymerized microtubule length per min was calculated. Thereafter interpolation ceased and the density of microtubules declined. The sample applied to developing xylem except that, because wall-thickening is localized rather than widespread, the rise and subsequent fall in the density of microtubules was less marked. The data are discussed in relation to the participation of microtubules in wall deposition and to the hypothesis that cortical microtubules arise in discrete zones along the edges of cells.

scholarly journals Mitotic antipairing of homologous and sex chromosomes via spatial restriction of two haploid sets

2018 ◽  
Vol 115 (52) ◽  
pp. E12235-E12244 ◽  
Author(s):  
Lisa L. Hua ◽  
Takashi Mikawa
Keyword(s):  
Genome Instability ◽  
Cell Types ◽  
Parental Origin ◽  
Meridional Plane ◽  
Homologous Chromosomes ◽  
Daughter Cells ◽  
Homologous Chromosome Pairing ◽  
Multiple Cell ◽  
Mouse Cells ◽  
Nuclear Polarity

Pairing homologous chromosomes is required for recombination. However, in nonmeiotic stages it can lead to detrimental consequences, such as allelic misregulation and genome instability, and is rare in human somatic cells. How mitotic recombination is prevented—and how genetic stability is maintained across daughter cells—is a fundamental, unanswered question. Here, we report that both human and mouse cells impede homologous chromosome pairing by keeping two haploid chromosome sets apart throughout mitosis. Four-dimensional analysis of chromosomes during cell division revealed that a haploid chromosome set resides on either side of a meridional plane, crossing two centrosomes. Simultaneous tracking of chromosome oscillation and the spindle axis, using fluorescent CENP-A and centrin1, respectively, demonstrates collective genome behavior/segregation of two haploid sets throughout mitosis. Using 3D chromosome imaging of a translocation mouse with a supernumerary chromosome, we found that this maternally derived chromosome is positioned by parental origin. These data, taken together, support the identity of haploid sets by parental origin. This haploid set-based antipairing motif is shared by multiple cell types, doubles in tetraploid cells, and is lost in a carcinoma cell line. The data support a mechanism of nuclear polarity that sequesters two haploid sets along a subcellular axis. This topological segregation of haploid sets revisits an old model/paradigm and provides implications for maintaining mitotic fidelity.

scholarly journals Daughter cells of Saccharomyces cerevisiae from old mothers display a reduced life span.

1994 ◽  
Vol 127 (6) ◽  
pp. 1985-1993 ◽  
Author(s):  
B K Kennedy ◽  
N R Austriaco ◽  
L Guarente
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Life Span ◽  
Daughter Cell ◽  
Young Mothers ◽  
Young Mother ◽  
Yeast Saccharomyces Cerevisiae ◽  
Daughter Cells ◽  
Per Se ◽  
Mother Cells ◽  
Maximum Occurrence

The yeast Saccharomyces cerevisiae typically divides asymmetrically to give a large mother cell and a smaller daughter cell. As mother cells become old, they enlarge and produce daughter cells that are larger than daughters derived from young mother cells. We found that occasional daughter cells were indistinguishable in size from their mothers, giving rise to a symmetric division. The frequency of symmetric divisions became greater as mother cells aged and reached a maximum occurrence of 30% in mothers undergoing their last cell division. Symmetric divisions occurred similarly in rad9 and ste12 mutants. Strikingly, daughters from old mothers, whether they arose from symmetric divisions or not, displayed reduced life spans relative to daughters from young mothers. Because daughters from old mothers were larger than daughters from young mothers, we investigated whether an increased size per se shortened life span and found that it did not. These findings are consistent with a model for aging that invokes a senescence substance which accumulates in old mother cells and is inherited by their daughters.

scholarly journals Generation of asymmetry during development. Segregation of type-specific proteins in Caulobacter.

1979 ◽  
Vol 81 (1) ◽  
pp. 123-136 ◽  
Author(s):  
N Agabian ◽  
M Evinger ◽  
G Parker
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Messenger Rna ◽  
Cell Types ◽  
Specific Protein ◽  
Soluble Proteins ◽  
Specific Cell ◽  
Daughter Cells ◽  
Specific Proteins ◽  
Entire Cell

An essential event in developmental processes is the introduction of asymmetry into an otherwise undifferentiated cell population. Cell division in Caulobacter is asymmetric; the progeny cells are structurally different and follow different sequences of development, thus providing a useful model system for the study of differentiation. Because the progeny cells are different from one another, there must be a segregation of morphogenetic and informational components at some time in the cell cycle. We have examined the pattern of specific protein segregation between Caulobacter stalked and swarmer daughter cells, with the rationale that such a progeny analysis would identify both structurally and developmentally important proteins. To complement the study, we have also examined the pattern of protein synthesis during synchronous growth and in various cellular fractions. We show here, for the first time, that the association of proteins with a specific cell type may result not only from their periodicity of synthesis, but also from their pattern of distribution at the time of cell division. Several membrane-associated and soluble proteins are segregated asymmetrically between progeny stalked and swarmer cells. The data further show that a subclass of soluble proteins becomes associated with the membrane of the progeny stalked cells. Therefore, although the principal differentiated cell types possess different synthetic capabilities and characteristic proteins, the asymmetry between progeny stalked and swarmer cells is generated primarily by the preferential association of specific soluble proteins with the membrane of only one daughter cell. The majority of the proteins which exhibit this segregation behavior are synthesized during the entire cell cycle and exhibit relatively long, functional messenger RNA half-lives.

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