Cellular asymmetry in Chlamydomonas reinhardtii

1989 ◽  
Vol 94 (2) ◽  
pp. 273-285 ◽  
Author(s):  
J.A. Holmes ◽  
S.K. Dutcher
Keyword(s):  
Chlamydomonas Reinhardtii ◽  
Basal Body ◽  
Flagellar Apparatus ◽  
Spindle Pole ◽  
The Other ◽  
Unicellular Alga ◽  
Phototactic Behavior ◽  
Cellular Asymmetry ◽  
Asymmetric Fusion ◽  
Two Sides

Although largely bilaterally symmetric, the two sides of the unicellular alga Chlamydomonas reinhardtii can be distinguished by the location of the single eyespot. When viewed from the anterior end, the eyespot is always closer to one flagellum than the other, and located at an angle of approximately 45 degrees clockwise of the flagellar plane. This location correlates with the position of one of four acetylated microtubule bundles connected to the flagellar apparatus. Each basal body is attached to two of these microtubule rootlets. The rootlet that positions the eyespot is always attached to the same basal body, which is the daughter of the parental/daughter basal body pair. At mitosis, the replicated basal body pairs segregate in a precise orientation that maintains the asymmetry of the cell and results in mitotic poles that have an invariant handedness. The fusion of gametic cells during mating is also asymmetric. As a result of asymmetric, but different, locations of the plus and minus mating structures, mating preferentially results in quadriflagellate dikaryons with parallel flagellar pairs and both eyespots on the same side of the cell. This asymmetric fusion, as well as all the other asymmetries described, may be necessary for the proper phototactic behavior of these cells. The invariant handedness of the spindle pole, eyespot position, and mating structure position appears to be based on the inherent asymmetry of the basal body pair, providing an example of how an intracellular pattern can be determined and maintained.

Ultrastructure and development of the flagellar apparatus and flagellar motion in the colonial graeen alga Astrephomene gubernaculifera

1983 ◽  
Vol 63 (1) ◽  
pp. 21-41
Author(s):  
H.J. Hoops ◽  
G.L. Floyd
Keyword(s):  
Basal Body ◽  
Rotational Symmetry ◽  
Amorphous Material ◽  
Flagellar Apparatus ◽  
The Other ◽  
Basal Bodies ◽  
Mature Cell ◽  
Embryonic Cleavage ◽  
Development Proceeds ◽  
Concurrent Events

Immediately following embryonic cleavage, the cells of Astrephomene have four equal-sized basal bodies, two of which are connected by a striated distal fibre and two striated proximal fibres. The four microtubular rootlets, which alternate between having 3/1 and 2 members, are arranged cruciately. The two basal bodies that are connected by the striated fibres then extend into flagella, while the two accessory basal bodies are now markedly shorter. At this stage the flagellar apparatus has 180 degrees rotational symmetry and is very similar to the flagellar apparatus of the unicellular Chlamydomonas and related algae. Development proceeds with a number of concurrent events. The basal bodies begin to separate at their proximal ends and become nearly parallel. Each striated proximal fibre detaches at one end from one of the basal bodies. Each half of the flagellar apparatus, which consists of a flagellum and attached basal body, an accessory basal body, two rootlets and a striated fibre (formerly one of the proximal striated fibres), rotates about 90 degrees, the two halves rotating in opposite directions. An electron-dense strut forms near one two-membered rootlet and grows past both basal bodies. During this time a fine, fibrous component appears between newly developed spade-like structures and associated amorphous material connected to each basal body. The basal bodies continue to separate as the distal fibre stretches and finally detaches from one of them. These processes result in the loss of the 180 degree rotational symmetry present in previous stages. Although the flagella continue to separate, there is no further reorganization of the components of the flagellar apparatus. In the mature cell of Astrephomene, the two flagella are inserted separately and are parallel. The four microtubular rootlets are no longer arranged cruciately. Three of the rootlets are nearly parallel, while the fourth is approximately perpendicular to the other three. A straited fibre connects each basal body to the underside of the strut. These fibres run in the direction of the effective stroke of the flagella and might be important either in anchoring the basal bodies or in the initiation of flagellar motion. Unlike the case in the unicellular Chlamydomonas, the two flagella beat in the same direction and in parallel planes. The flagella of a given cell may or may not beat in synchrony. The combination of this type of flagellar motion and the parallel, separate flagella appears to be suited to the motion of this colonial organism.

scholarly journals Basal Body Duplication and Maintenance Require One Member of the Tetrahymena thermophila Centrin Gene Family

2005 ◽  
Vol 16 (8) ◽  
pp. 3606-3619 ◽  
Author(s):  
Alexander J. Stemm-Wolf ◽  
Garry Morgan ◽  
Thomas H. Giddings ◽  
Erin A. White ◽  
Robb Marchione ◽  
...  
Keyword(s):  
Basal Body ◽  
Calcium Binding ◽  
Tetrahymena Thermophila ◽  
Essential Gene ◽  
Expression Patterns ◽  
Spindle Pole ◽  
The Other ◽  
Basal Bodies ◽  
Spindle Pole Bodies ◽  
Ef Hand

Centrins, small calcium binding EF-hand proteins, function in the duplication of a variety of microtubule organizing centers. These include centrioles in humans, basal bodies in green algae, and spindle pole bodies in yeast. The ciliate Tetrahymena thermophila contains at least four centrin genes as determined by sequence homology, and these have distinct localization and expression patterns. CEN1's role at the basal body was examined more closely. The Cen1 protein localizes primarily to two locations: one is the site at the base of the basal body where duplication is initiated. The other is the transition zone between the basal body and axoneme. CEN1 is an essential gene, the deletion of which results in the loss of basal bodies, which is likely due to defects in both basal body duplication and basal body maintenance. Analysis of the three other centrins indicates that two of them function at microtubule-rich structures unique to ciliates, whereas the fourth is not expressed under conditions examined in this study, although when artificially expressed it localizes to basal bodies. This study provides evidence that in addition to its previously known function in the duplication of basal bodies, centrin is also important for the integrity of these organelles.

scholarly journals Centrin Scaffold in Chlamydomonas reinhardtii Revealed by Immunoelectron Microscopy

2005 ◽  
Vol 4 (7) ◽  
pp. 1253-1263 ◽  
Author(s):  
Stefan Geimer ◽  
Michael Melkonian
Keyword(s):  
Chlamydomonas Reinhardtii ◽  
Immunoelectron Microscopy ◽  
Basal Body ◽  
Flagellar Apparatus ◽  
Single Copy ◽  
Asymmetric Structure ◽  
Transitional Region ◽  
Ef Hand ◽  
Basal Apparatus ◽  
Postembedding Immunoelectron Microscopy

ABSTRACT In the flagellate green alga Chlamydomonas reinhardtii the Ca2+-binding EF-hand protein centrin is encoded by a single-copy gene. Previous studies have localized the protein to four distinct structures in the flagellar apparatus: the nucleus-basal body connector, the distal connecting fiber, the flagellar transitional region, and the axoneme. To explain the disjunctive distribution of centrin, the interaction of centrin with as yet unknown specific centrin-binding proteins has been implied. Here, we demonstrate using serial section postembedding immunoelectron microscopy of isolated cytoskeletons that centrin is located in additional structures (transitional fibers and basal body lumen) and that the centrin-containing structures of the basal apparatus are likely part of a continuous filamentous scaffold that extends from the nucleus to the flagellar bases. In addition, we show that centrin is located in the distal lumen of the basal body in a rotationally asymmetric structure, the V-shaped filament system. This novel centrin-containing structure has also been detected near the distal end of the probasal bodies. Taken together, these results suggest a role for a rotationally asymmetric centrin “seed” in the growth and development of the centrin scaffold following replication of the basal apparatus.

Eurasian "Theory of Economy Management" as an Organic Part of the Russian Economic School

2003 ◽  
pp. 95-110
Author(s):  
M. Voeykov
Keyword(s):  
Economic Development ◽  
Theoretical Model ◽  
Initial Step ◽  
State Regulation ◽  
Soviet Economy ◽  
The Other ◽  
Large Share ◽  
Organic Part ◽  
Two Sides ◽  
Enterprise Activity

The original version of "the theory of economy management", developed in the 1920s by Russian economists-emigrants who called themselves "Eurasians" (N. Trubetskoy, P. Savitskiy, etc.) is analyzed in the article. They considered this theory to be the basis of the original Russia's way of economic development. The Eurasian theory of economy management focuses on two sides of enterprise activity: managerial as well as social and moral. The Eurasians accepted the Soviet economy with the large share of state regulation as the initial step of development. On the other hand they paid much attention to the private sector activity. Eurasians developed a theoretical model of the mixed economy which can be attributed as the Russian economic school.

The Other Side Of The Coin: An Enquiry Into The Difficulties And Apprehensions Encountered By Consumers With Green Products

2019 ◽  
Vol 118 (8) ◽  
pp. 152-159
Author(s):  
Jijimon M J ◽  
Dr. S. Anthony Rahul Golden ◽  
Dr. S. Bulomine Regi
Keyword(s):  
The Other ◽  
Green Products ◽  
Two Sides

Every reality has its own positives and negatives. As the proverb goes coin has two sides. It is very much true in the case of green products too. There is no doubt that green products have many benefits and positives. Despite all the good things about green products, there exist a few glitches and shadows, thereby creating a few doubts and apprehensions in the minds of consumers. The present paper tries to understand these problems associated with green products from the perspectives of the consumers and analyses them with an intention of providing the green brands the means and ways to eliminate such anomalies. The study finds out that the unavailability of products is the most difficult thing the consumers have experienced while purchasing.

Size Selectivity of Diamond and Square Mesh Codends in Pelagic Herring Trawls: Only Small Herring Will Notice the Difference

1992 ◽  
Vol 49 (10) ◽  
pp. 2104-2117 ◽  
Author(s):  
Petri Suuronen ◽  
Russell B. Millar
Keyword(s):  
Relative Size ◽  
Mesh Size ◽  
The Other ◽  
Size Selectivity ◽  
The Difference ◽  
Catch Rates ◽  
Two Sides ◽  
High Catch

A twin codend trawl was fished in the northern Baltic to study the size selectivity of square mesh and diamond mesh codends of 36-mm nominal mesh size. For each codend, 15 hauls were completed with a small mesh (20 mm) codend deployed on the other side of the trawl. The relative size of the catches in the two sides of the trawl varied considerably from haul to haul (the separator section was not operating properly) and selection curves were estimated from each individual haul using a method that incorporated the differences in catching efficiency of the two sides. The length of 50% retention decreased with increased catch for both the diamond and square mesh codends, although in neither case was this relationship statistically significant. Selection curves fitted to the combined haul data were asymmetric. The square mesh codend retained significantly less small herring than the diamond mesh codend, and for larger herring the two codends had similar selectivity. In both codends, most escapes occurred at the front of the catch bulge, from the upper side of the codend. At high catch rates, mesh blockage was observed for several metres ahead of the catch bulge during the later part of the tow.

Asymmetry of the spindle pole bodies and spg1p GAP segregation during mitosis in fission yeast

1999 ◽  
Vol 112 (14) ◽  
pp. 2313-2321 ◽  
Author(s):  
L. Cerutti ◽  
V. Simanis
Keyword(s):  
Cell Cycle ◽  
Fission Yeast ◽  
Spindle Pole Body ◽  
Mitotic Cell ◽  
Spindle Pole ◽  
The Other ◽  
Septum Formation ◽  
Spindle Pole Bodies ◽  
Interphase Cells ◽  
Early Mitosis

In the fission yeast Schizosaccharomyces pombe, the onset of septum formation is induced by a signal transduction network involving several protein kinases and a GTPase switch. One of the roles of the spg1p GTPase is to localise the cdc7p protein kinase to the poles of the mitotic spindle, from where the onset of septation is thought to be signalled at the end of mitosis. Immunofluorescence studies have shown that cdc7p is located on both spindle pole bodies early in mitosis, but only on one during the later stages of anaphase. This is mediated by inactivation of spg1p on one pole before the other. The GAP for spg1p is a complex of two proteins, cdc16p and byr4p. Localisation of cdc16p and byr4p by indirect immunofluorescence during the mitotic cell cycle showed that both proteins are present on the spindle pole body in interphase cells. During mitosis, byr4p is seen first on both poles of the spindle, then on only one. This occurs prior to cdc7p becoming asymmetric. In contrast, the signal due to cdc16p decreases to a low level during early mitosis, before being seen strongly on the same pole as byr4p. Double staining indicates that this is the opposite pole to that which retains cdc7p in late anaphase. Examination of the effect of inactivating cdc16p at various stages of the cell cycle suggests that cdc16p, together with cdc2p plays a role in restraining septum formation during interphase. The asymmetric inactivation of spg1p is mediated by recruitment of the cdc16p-byr4p GAP to one of the poles of the spindle before the other, and the asymmetry of the spindle pole bodies may be established early during mitosis. Moreover, the spindle pole bodies appear to be non-equivalent even after division has been completed.

scholarly journals Exploring language attitudes in ELF research: Contrasting approaches in conversation

2016 ◽  
Vol 3 (4) ◽  
pp. 74-109 ◽  
Author(s):  
Tomokazu Ishikawa ◽  
Sonia Morán Panero
Keyword(s):  
Present Article ◽  
Social Practice ◽  
Language Attitudes ◽  
A Priori ◽  
The Other ◽  
Research Projects ◽  
Doctoral Research ◽  
Two Sides ◽  
Ontological Position ◽  
Linguistic Phenomenon

AbstractWith reference to two recent doctoral research projects on ELF, the present article examines the characterisation of language attitudes as either stable or variable evaluative phenomena, and provides a detailed account of methodological practices that may be favoured from each ontological position. The durability of language attitudes is more specifically conceptualised as a stable (but not enduring) construct directed to a linguistic phenomenon in one thesis, and as variable and emergent forms of evaluative social practice around a language-related issue in the other. With these two different approaches in conversation, the authors consider the extent to which stability and variability of language attitudes may be two sides of the same coin, and question whether it is safe to assume a priori the inferability of stable language attitudes from the observation of evaluative practice. This article evidences the need for ELF researchers working in this area to contemplate what and how it is being researched in the name of language attitudes while having awareness of possible alternatives in any given study.

scholarly journals PHOTIC STIMULATION AND LEG MOVEMENTS IN THE CRAYFISH

1933 ◽  
Vol 16 (6) ◽  
pp. 905-910 ◽  
Author(s):  
B. Kropp ◽  
E. V. Enzmann
Keyword(s):  
The Other ◽  
Photic Stimulation ◽  
Two Sides ◽  
Leg Movements

When Cambarus clarkii is exposed to a source of light so that both eyes are equally illuminated, leg movements of the two sides are equal in frequency and amplitude. On covering one eye and exposing the uncovered eye to light, leg movements on the side of the uncovered eye are more frequent and are of greater amplitude than on the side of the covered eye. On covering the exposed eye also the leg movements on the two sides again tend to become equal in frequency and amplitude. When one eye is lost and the other remains functional, the leg movements on the side of the lost eye will be similar to those on the side of a normal, covered eye.

scholarly journals Probability and loss: two sides of the risk assessment coin

2011 ◽  
Vol 35 (11) ◽  
pp. 413-418 ◽  
Author(s):  
Matthew M. Large ◽  
Olav B. Nielssen
Keyword(s):  
Mental Health ◽  
Risk Assessment ◽  
Decision Making ◽  
Clinical Decision Making ◽  
Clinical Decision ◽  
The Other ◽  
Current Form ◽  
Mental Health Settings ◽  
Future Harm ◽  
Two Sides

SummaryRisk assessment has been widely adopted in mental health settings in the hope of preventing harms such as violence to others and suicide. However, risk assessment in its current form is mainly concerned with the probability of adverse events, and does not address the other component of risk – the extent of the resulting loss. Although assessments of the probability of future harm based on actuarial instruments are generally more accurate than the categorisations made by clinicians, actuarial instruments are of little assistance in clinical decision-making because there is no instrument that can estimate the probability of all the harms associated with mental illness, or estimate the extent of the resulting losses. The inability of instruments to distinguish between the risk of common but less serious harms and comparatively rare catastrophic events is a particular limitation of the value of risk categorisations. We should admit that our ability to assess risk is severely limited, and make clinical decisions in a similar way to those in other areas of medicine – by informed consideration of the potential consequences of treatment and non-treatment.

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