scholarly journals Role of nucleation in cortical microtubule array organization: variations on a theme

2013 ◽  
Vol 75 (2) ◽  
pp. 270-277 ◽  
Author(s):  
Erica A. Fishel ◽  
Ram Dixit
Keyword(s):  
Cortical Microtubule ◽  
Microtubule Array ◽  
Variations On A Theme

scholarly journals How selective severing by katanin promotes order in the plant cortical microtubule array

2017 ◽  
Vol 114 (27) ◽  
pp. 6942-6947 ◽  
Author(s):  
Eva E. Deinum ◽  
Simon H. Tindemans ◽  
Jelmer J. Lindeboom ◽  
Bela M. Mulder
Keyword(s):  
Theoretical Perspective ◽  
Cortical Microtubule ◽  
Underlying Mechanism ◽  
Microtubule Array ◽  
Microtubule Severing ◽  
Anisotropic Expansion ◽  
Sufficient And Necessary Conditions ◽  
Asymmetric Growth ◽  
The One

Plant morphogenesis requires differential and often asymmetric growth. A key role in controlling anisotropic expansion of individual cells is played by the cortical microtubule array. Although highly organized, the array can nevertheless rapidly change in response to internal and external cues. Experiments have identified the microtubule-severing enzyme katanin as a central player in controlling the organizational state of the array. Katanin action is required both for normal alignment and the adaptation of array orientation to mechanical, environmental, and developmental stimuli. How katanin fulfills its controlling role, however, remains poorly understood. On the one hand, from a theoretical perspective, array ordering depends on the “weeding out” of discordant microtubules through frequent catastrophe-inducing collisions among microtubules. Severing would reduce average microtubule length and lifetime, and consequently weaken the driving force for alignment. On the other hand, it has been suggested that selective severing at microtubule crossovers could facilitate the removal of discordant microtubules. Here we show that this apparent conflict can be resolved by systematically dissecting the role of all of the relevant interactions in silico. This procedure allows the identification of the sufficient and necessary conditions for katanin to promote array alignment, stresses the critical importance of the experimentally observed selective severing of the “crossing” microtubule at crossovers, and reveals a hitherto not appreciated role for microtubule bundling. We show how understanding the underlying mechanism can aid with interpreting experimental results and designing future experiments.

The role of long non-coding RNAs in chromatin structure and gene regulation: variations on a theme

2008 ◽  
Vol 389 (4) ◽  
pp. 323-331 ◽  
Author(s):  
David Umlauf ◽  
Peter Fraser ◽  
Takashi Nagano
Keyword(s):  
Gene Expression ◽  
Gene Regulation ◽  
Chromatin Structure ◽  
Genome Architecture ◽  
Paradoxical Situation ◽  
Intergenic Regions ◽  
Non Coding Rnas ◽  
Variations On A Theme

Abstract Transcriptome studies have uncovered a plethora of non-coding RNAs (ncRNA) in mammals. Most originate within intergenic regions of the genome and recent evidence indicates that some are involved in many different pathways that ultimately act on genome architecture and gene expression. In this review, we discuss the role of well-characterized long ncRNAs in gene regulation pointing to their similarities, but also their differences. We will attempt to highlight a paradoxical situation in which transcription is needed to repress entire chromosomal domains possibly through the action of ncRNAs that create nuclear environments refractory to transcription.

scholarly journals A plausible mechanism for longitudinal lock-in of cortical microtubule array after light-induced reorientation

2020 ◽  
Author(s):  
Marco Saltini ◽  
Bela M. Mulder
Keyword(s):  
Alternative Hypothesis ◽  
Cortical Microtubule ◽  
Selective Advantage ◽  
Consensus Model ◽  
Microtubule Array ◽  
Orientation State ◽  
Cortical Array ◽  
Plausible Mechanism ◽  
Lock In

The light-induced reorientation of the cortical microtubule array in dark-grown A. thaliana hypocotyl cells is a striking example of the dynamical plasticity of the microtubule cytoskeleton. A consensus model, based on katanin-mediated severing at microtubule crossovers, has been developed that successfully describes the onset of the observed switch between a transverse and longitudinal array orientation. However, we currently lack an understanding of of why the newly populated longitudinal array direction remains stable for longer times, when the initial trigger for the reorientation has died out, and re-equilibration effects would tend to drive the system back to a mixed orientation state. Using both simulations and analytical calculations, we show that the assumption of a small orientation-dependent shift in microtubule dynamics is sufficient to explain the long term lock-in of the longitudinal array orientation. Furthermore, we show that the natural alternative hypothesis that there is a selective advantage in severing longitudinal microtubules, is neither necessary nor sufficient to achieve cortical array reorientation, but is able to accelerate this process significantly.

Structure and development of cortical microtubule arrays in plant cells

1978 ◽  
Vol 36 (2) ◽  
pp. 264-265
Author(s):  
A.R. Hardham ◽  
B.E.S. Gunning
Keyword(s):  
Cell Wall ◽  
Plasma Membrane ◽  
Cortical Microtubule ◽  
Plant Cells ◽  
Original Description ◽  
Cell Cortex ◽  
Cortical Microtubules ◽  
Fundamental Part ◽  
Cellulose Component

Microtubules in the plant cell cortex are usually aligned parallel to microfibrils of cellulose that are being deposited in the cell wall, and are considered to function in guiding or orienting cellulose synthetase complexes that lie in or on the plasma membrane. The cellulose component is largely responsible for the mechanical reaction of the wall to turgor forces, thereby determining cell size and shape, and therefore the role of the cortical microtubules is a fundamental part of the overall morphogenetic process in plants. It is important to determine the structure of cortical arrays of microtubules and to learn how the cell regulates their development, neither of these aspects having been investigated adequately since the original description likened the microtubules to “hundreds of hoops around the cell”.

John W. MeDor and Gunvant M. Desai (eels.). Agricultural Change and Rural Poverty - Variations on a Theme by Dharm Narain. Baltimore & London: The Johns Hopkins University Press. 1985. xix + 233 pp. Illustrations: bibliography; index.

1986 ◽  
Vol 25 (2) ◽  
pp. 193-196
Author(s):  
Luther Tweeten
Keyword(s):  
Technological Change ◽  
Technological Progress ◽  
Green Revolution ◽  
Rural Poverty ◽  
Agricultural Change ◽  
Extensive Data ◽  
Johns Hopkins University ◽  
Variations On A Theme ◽  
Trickle Down

It is fashionable in some intellectual circles to deride the trickle-down theory, technological change, and the Green Revolution as tools of the haves to exploit the have-nots. In a worthwhile book, drawing especially on extensive data for India, several distinguished analysts from various countries examined sources of rural poverty with special attention to the role of technological progress and the trickledown theory.

scholarly journals Role of the centrosome in organizing the interphase microtubule array: properties of cytoplasts containing or lacking centrosomes.

1984 ◽  
Vol 98 (5) ◽  
pp. 1763-1776 ◽  
Author(s):  
E Karsenti ◽  
S Kobayashi ◽  
T Mitchison ◽  
M Kirschner
Keyword(s):  
Critical Concentration ◽  
Spatial Arrangement ◽  
Degree Of Polymerization ◽  
Microtubule Depolymerization ◽  
Microtubule Organization ◽  
Drug Induced ◽  
Microtubule Array ◽  
Growth State ◽  
Original Culture

To study the role of the centrosome in microtubule organization in interphase cells, we developed a method for obtaining cytoplasts (cells lacking a nucleus) that did or did not contain centrosomes. After drug-induced microtubule depolymerization, cytoplasts with centrosomes made from sparsely plated cells reconstituted a microtubule array typical of normal cells. Under these conditions cytoplasts without centrosomes formed only a few scattered microtubules. This difference in degree of polymerization suggests that centrosomes affect not only the distribution but the amount of microtubules in cells. To our surprise, the extent of microtubules assembled increased with the cell density of the original culture. At confluent density, cytoplasts without centrosomes had many microtubules, equivalent to cytoplasts with centrosomes. The additional microtubules were arranged peripherally and differed from the centrosomal microtubules in their sensitivity to nocodazole. These and other results suggest that the centrosome stabilizes microtubules in the cell, perhaps by capping one end. Microtubules with greater sensitivity to nocodazole arise by virtue of change in the growth state of the cell and may represent free or uncapped polymers. These experiments suggest that the spatial arrangement of microtubules may change by shifting the total tubulin concentration or the critical concentration for assembly.

Music Therapy: Variations on a Theme

1993 ◽  
Vol 9 (4) ◽  
pp. 37-39 ◽  
Author(s):  
Susan E. Mandel
Keyword(s):  
Quality Of Life ◽  
Music Therapy ◽  
Terminally Ill ◽  
Music Therapists ◽  
Music Therapist ◽  
Service Training ◽  
Variations On A Theme ◽  
Therapy Service

Music therapists make significant contributions to the multidisciplinary hospice team in its efforts to provide holistic palliative care to terminally ill patients and family members and to promote quality of life. The role of a hospice music therapist is described, including providing direct patient music therapy service, training the hospice team in music therapy, developing and maintaining a music therapy resource centre, and offering bereavement services. A review of patient charts Provides information about patient age, sex, diagnosis, and source and reasons for referral.

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