Ultrastructure of the Gaertneriomyces zoospore (Spizellomycetales, Chytridiomycetes)

1981 ◽  
Vol 59 (1) ◽  
pp. 83-90 ◽  
Author(s):  
Donald J. S. Barr
Keyword(s):  
Endoplasmic Reticulum ◽  
New Order ◽  
Microtubule Organizing Center ◽  
Organizing Center

The zoospore type is described for Gaertneriomyces, a genus in the new order Spizellomycetales, Chytridiomycetes. The nucleus lies in the posterior of the zoospore and it has a basal concavity. The kinetosome and nonfunctional centriole are located just distally to the concavity. Microtubulules radiate in the cytoplasm from a presumed microtubule organizing center consisting of two short, electron-opaque bars attached to the kinetosome. Mitochondria are predominantly in the posterior, and aggregates of lipid globules in the anterior of the zoospore. Microbodies are morphologically associated with the lipid and endoplasmic reticulum. They are also found along the sides of the nucleus and near the mitochondria.

Cytological variation in zoospores of Spizellomyces (Chytridiomycetes)

1984 ◽  
Vol 62 (6) ◽  
pp. 1202-1208 ◽  
Author(s):  
Donald J. S. Barr
Keyword(s):  
Endoplasmic Reticulum ◽  
Microtubule Organizing Center ◽  
Fibrillar Material ◽  
Organizing Center ◽  
Cytological Features ◽  
Cytological Characteristics

The principal cytological features and their variations are described in zoospores of 38 isolates belonging to seven species of Spizellomyces. This genus is distinguished from others in the Spizellomycetaceae by the orientation of the microtubules and the position of the nucleus relative to the kinetosome in the zoospore. Microtubules run apparently at random into the cytoplasm from a microtubule-organizing center (spur) on one side of the kinetosome. The nucleus is anteriorly or centrally positioned with a heel-like process extending to near the proximal face of the kinetosome, or it can be posteriorly positioned and elongate with one end close to the kinetosome. Differences between species are reflected by the position and shape of the nucleus, the extent of the endoplasmic reticulum which in some species circumscribes lipid globules, the presence or absence of an apparent connection by fibrillar material between the kinetosome and a nonfunctional centriole, and the morphology of the microtubule-organizing center. The zoospores of Spizellomyces punctatus (Koch) D. Barr, S. plurigibbosus (D. Barr) D. Barr, and S. palustris (Gaertner) D. Barr are cytologically similar, but those of S. acuminatus (D. Barr) D. Barr, S. dolichospermus D. Barr, S. lactosolyticus D. Barr and S. pseudodichotomus (Umphlett) D. Barr each have one or more distinctive characteristic. Spizellomyces dolichospermus and S. pseudodichotomus also have some cytological characteristics in common with the genus Kochiomyces.

Monoplastidy in spermatogenesis of Lycopodium obscurum

1994 ◽  
Vol 72 (10) ◽  
pp. 1436-1444 ◽  
Author(s):  
Karen Sue Renzaglia ◽  
Angel R. Maden ◽  
Jeffrey G. Duckett ◽  
Dean P. Whittier
Keyword(s):  
Endoplasmic Reticulum ◽  
Key Words ◽  
Mother Cell ◽  
Annulate Lamellae ◽  
Microtubule Organizing Center ◽  
Microtubule Organizing Centers ◽  
Cell Divisions ◽  
Organizing Center ◽  
Spindle Microtubules ◽  
Spindle Development

Unlike Lycopodium laterale, which is polyplastidic during spermatogenesis, Lycopodium obscurum exhibits monoplastidy beginning in the early proliferative stages of antheridial development. Previous cell generations are polyplastidic and plastid fusion involving connective cylinders establishes the monoplastidic condition. Plastid and nuclear divisions are coordinated in L. obscurum with the plastids positioned at opposite poles prior to spindle development. Unlike monoplastidic cell divisions with morphogenetic plastid migration and polarity in other lycophytes, mosses, and hornworts, however, the spindles in L. obscurum do not originate from the plastid envelopes but from endoplasmic reticulum positioned against the plastid. In the final divisions, spindle microtubules emanate from structurally defined microtubule organizing centers that develop between the plastids and nucleus. Preceding the appearance of centrioles in the spermatid mother cell, the centrosomes comprise electron-dense granular matrices with associated vesicles and endoplasmic reticulum. Among archegoniate microtubule organizing centers, the discrete acentriolar centrosomes of Lycopodium most closely resemble the microtubule organizing centers in moss spore development and the polar organizer of liverwort mitosis. Key words: annulate lamellae, centrosome, Lycopodium, microtubule organizing center, monoplastidy, plastid dividing ring.

scholarly journals Regulation of Blos1 by IRE1 prevents the accumulation of Huntingtin protein aggregates

2021 ◽  
Author(s):  
Donghwi Bae ◽  
Rachel Elizabeth Jones ◽  
Julie Hollien
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Death ◽  
Huntington's Disease ◽  
Cultured Cells ◽  
Protein Aggregates ◽  
Mutant Huntingtin ◽  
Microtubule Organizing Center ◽  
Huntingtin Protein ◽  
Late Endosomes ◽  
Organizing Center

Huntington's Disease is characterized by accumulation of the aggregation-prone mutant Huntingtin (mHTT) protein. Here, we show that expression of mHTT in mouse cultured cells activates IRE1, the transmembrane sensor of stress in the endoplasmic reticulum, leading to degradation of the Blos1 mRNA and repositioning of lysosomes and late endosomes toward the microtubule organizing center. Overriding Blos1 degradation results in accumulation of larger mHTT aggregates and increased cell death. Although mHTT is degraded by macroautophagy when highly expressed, we show that prior to the formation of large aggregates, mHTT is degraded via an ESCRT-dependent, endosomal microautophagy pathway. This pathway is enhanced by Blos1 degradation and appears to protect cells from a toxic, less aggregated form of mHTT.

Three-Dimensional reconstruction of isolated centrosomes by automated electron tomography

1994 ◽  
Vol 52 ◽  
pp. 310-311
Author(s):  
M.B. Braunfeld ◽  
M. Moritz ◽  
B.M. Alberts ◽  
J.W. Sedat ◽  
D.A. Agard
Keyword(s):  
Electron Tomography ◽  
Three Dimensional ◽  
Vital Role ◽  
Complex Nature ◽  
Animal Cells ◽  
Microtubule Organizing Center ◽  
Nucleation Sites ◽  
Dimensional Reconstruction ◽  
Organizing Center ◽  
Resolution Model

In animal cells, the centrosome functions as the primary microtubule organizing center (MTOC). As such the centrosome plays a vital role in determining a cell's shape, migration, and perhaps most importantly, its division. Despite the obvious importance of this organelle little is known about centrosomal regulation, duplication, or how it nucleates microtubules. Furthermore, no high resolution model for centrosomal structure exists.We have used automated electron tomography, and reconstruction techniques in an attempt to better understand the complex nature of the centrosome. Additionally we hope to identify nucleation sites for microtubule growth.Centrosomes were isolated from early Drosophila embryos. Briefly, after large organelles and debris from homogenized embryos were pelleted, the resulting supernatant was separated on a sucrose velocity gradient. Fractions were collected and assayed for centrosome-mediated microtubule -nucleating activity by incubating with fluorescently-labeled tubulin subunits. The resulting microtubule asters were then spun onto coverslips and viewed by fluorescence microscopy.

Genetic interactions between CDC31 and KAR1, two genes required for duplication of the microtubule organizing center in Saccharomyces cerevisiae.

Genetics ◽  
1994 ◽  
Vol 137 (2) ◽  
pp. 407-422 ◽  
Author(s):  
E A Vallen ◽  
W Ho ◽  
M Winey ◽  
M D Rose
Keyword(s):  
Copy Number ◽  
Gene Dosage ◽  
Spindle Pole Body ◽  
Direct Interaction ◽  
Spindle Pole ◽  
High Copy Number ◽  
Temperature Sensitive ◽  
Microtubule Organizing Center ◽  
Recessive Mutations ◽  
Organizing Center

Abstract KAR1 encodes an essential component of the yeast spindle pole body (SPB) that is required for karyogamy and SPB duplication. A temperature-sensitive mutation, kar1-delta 17, mapped to a region required for SPB duplication and for localization to the SPB. To identify interacting SPB proteins, we isolated 13 dominant mutations and 3 high copy number plasmids that suppressed the temperature sensitivity of kar1-delta 17. Eleven extragenic suppressor mutations mapped to two linkage groups, DSK1 and DSK2. The extragenic suppressors were specific for SPB duplication and did not suppress karyogamy-defective alleles. The major class, DSK1, consisted of mutations in CDC31. CDC31 is required for SPB duplication and encodes a calmodulin-like protein that is most closely related to caltractin/centrin, a protein associated with the Chlamydomonas basal body. The high copy number suppressor plasmids contained the wild-type CDC31 gene. One CDC31 suppressor allele conferred a temperature-sensitive defect in SPB duplication, which was counter-suppressed by recessive mutations in KAR1. In spite of the evidence for a direct interaction, the strongest CDC31 alleles, as well as both DSK2 alleles, suppressed a complete deletion of KAR1. However, the CDC31 alleles also made the cell supersensitive to KAR1 gene dosage, arguing against a simple bypass mechanism of suppression. We propose a model in which Kar1p helps localize Cdc31p to the SPB and that Cdc31p then initiates SPB duplication via interaction with a downstream effector.

scholarly journals Evidence for rapid structural and functional changes of the melanophore microtubule-organizing center upon pigment movements

1979 ◽  
Vol 83 (3) ◽  
pp. 623-632 ◽  
Author(s):  
M Schliwa ◽  
U Euteneuer ◽  
W Herzog ◽  
K Weber
Keyword(s):  
Complete Removal ◽  
Cell System ◽  
The State ◽  
Microtubule Assembly ◽  
Microtubule Organizing Center ◽  
Functional Changes ◽  
Organizing Center ◽  
Pigment Distribution ◽  
And Function ◽  
In Cells

Melanophores of the angelfish, pterophyllum scalare, have previously been shown to display approximately 2,400 microtubules in cells wih pigment dispersed; these microtubules radiate from a presumptive organizing center, the central apparatus (CA), and their number is reduced to approximately 1,000 in the state with aggregated pigment (M. Schliwa and U. Euteneuer, 1978, J. Supramol. Struct. 8:177-190). In an attempt to elucidate the factors controlling this rapid reorganization of the microtubule apparatus, structure and function of the CA have been investigated under different physiological conditions. As a function of the state of pigment distribution, melanophores differ markedly with respect to CA organization. A complex of dense amorphous aggregates and associated fuzzy material, several micrometers in diameter, surrounds the centrioles in cells with pigment dispersed, and numerous microtubules emanate from this complex in a radial fashion. In the aggregated state, on the other hand, few microtubules are observed in the pericentiolar region, and the amount of fibrous material is greatly reduced. These changes in CA morphology as a function of the state of pigment distribution are associated with a marked difference in its capacity to initiatiate the assembly of microtubules from exogenous pure porcine brain tubulin in lysed cell preparations. After complete removal of preexisting microtubules, cells lysed in the dispersed state into a solution of 1-2 mg/ml pure tubulin have numerous microtubules associated with the CA in radial fashion, while cells lysed in the aggregated state nucleate the assembly of only a few microtubules. We conclude that it is the activity of the CA that basically regulates the expression of microtubules. This regulation is achieved through a variation in the capacity to initiate microtubule assembly. Increase or decrease in the amount of dense material, as readily observed in the cell system studied here, seems to be a morphologic expression of such a physiologic function.

scholarly journals Murine Cytomegalovirus Capsid Assembly Is Dependent on US22 Family Gene M140 in Infected Macrophages

2009 ◽  
Vol 83 (15) ◽  
pp. 7449-7456 ◽  
Author(s):  
Laura K. Hanson ◽  
Jacquelyn S. Slater ◽  
Victoria J. Cavanaugh ◽  
William W. Newcomb ◽  
Lisa L. Bolin ◽  
...  
Keyword(s):  
Dna Cleavage ◽  
Early Gene ◽  
Murine Cytomegalovirus ◽  
Genome Replication ◽  
Microtubule Organizing Center ◽  
Viral Dna ◽  
Dnase Treatment ◽  
Organizing Center ◽  
Significant Impairment ◽  
The Stability

ABSTRACT Macrophages are an important target cell for infection with cytomegalovirus (CMV). A number of viral genes that either are expressed specifically in this cell type or function to optimize CMV replication in this host cell have now been identified. Among these is the murine CMV (MCMV) US22 gene family member M140, a nonessential early gene whose deletion (RVΔ140) leads to significant impairment in virus replication in differentiated macrophages. We have now determined that the defect in replication is at the stage of viral DNA encapsidation. Although the rate of RVΔ140 genome replication and extent of DNA cleavage were comparable to those for revertant virus, deletion of M140 resulted in a significant reduction in the number of viral capsids in the nucleus, and the viral DNA remained sensitive to DNase treatment. These data are indicative of incomplete virion assembly. Steady-state levels of both the major capsid protein (M86) and tegument protein M25 were reduced in the absence of the M140 protein (pM140). This effect may be related to the localization of pM140 to an aggresome-like, microtubule organizing center-associated structure that is known to target misfolded and overexpressed proteins for degradation. It appears, therefore, that pM140 indirectly influences MCMV capsid formation in differentiated macrophages by regulating the stability of viral structural proteins.

Peroxynitrite Deteriorates Oocyte Quality through Disassembly of Microtubule Organizing Center

2015 ◽  
Vol 87 ◽  
pp. S114
Author(s):  
Sana Khan ◽  
Faten Shaeib ◽  
Mili Thakur ◽  
Roohi Jeelani ◽  
Husam M Abu-Soud
Keyword(s):  
Oocyte Quality ◽  
Microtubule Organizing Center ◽  
Organizing Center
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