Kinetochores associated with the nuclear envelope in the mitosis of a dinoflagellate

This is the publisher's version, also available electronically from "http://jcb.rupress.org".No abstract availabl

γ-Tubulin complexes in microtubule nucleation and beyond

Tremendous progress has been made in understanding the functions of γ-tubulin and, in particular, its role in microtubule nucleation since the publication of its discovery in 1989. The structure of γ-tubulin has been determined, and the components of γ-tubulin complexes have been identified. Significant progress in understanding the structure of the γ-tubulin ring complex and its components has led to a persuasive model for how these complexes nucleate microtubule assembly. At the same time, data have accumulated that γ-tubulin has important but less well understood functions that are not simply a consequence of its function in microtubule nucleation. These include roles in the regulation of plus-end microtubule dynamics, gene regulation, and mitotic and cell cycle regulation. Finally, evidence is emerging that γ-tubulin mutations or alterations of γ-tubulin expression play an important role in certain types of cancer and in other diseases

Isolation of mip (microtubule interacting protein) mutations of Aspergillus nidulans

This is the publisher's version, also available electronically from "http://mcb.asm.org".We identified four mutations in two previously undescribed loci involved in microtubule function in Aspergillus nidulans as extragenic suppressors of benA33, a heat-sensitive beta-tubulin mutation. Three of the four mutations map to a locus closely linked to riboB on linkage group VIII; we designated this locus mipA (for microtubule-interacting protein). We were not able to map the remaining suppressor because of chromosomal rearrangements. However, since it recombines with riboB at a significantly higher frequency than the mipA alleles, it is unlikely to be in mipA; thus, we designated it mipB1. The mip mutations are not allelic to the previously identified loci that encode alpha- and beta-tubulin, and it is likely that mipA and mipB encode previously unidentified nontubulin proteins involved in microtubule function. Each of the mip mutations suppresses the heat sensitivity conferred by benA33 and suppresses the blockage of nuclear division and movement conferred by this mutation at high temperatures. Interactions between mipA and benA are allele specific. All of the mipA mutations are cryptic in a wild-type benA background but cause cold sensitivity in combination with benA33. These mutations also confer cold sensitivity in combination with benA31 and benA32 and reduce the resistance conferred by these mutations to the antimicrotubule agent benomyl but do not suppress the heat sensitivity conferred by these alleles. Finally, the mipA alleles suppress the heat sensitivity conferred by benA11, benA17, and benA21 but do not confer cold sensitivity in combination with these alleles

Prestige and content biases together shape the cultural transmission of narratives

Context-based cultural transmission biases such as prestige are thought to have been a primary driver in shaping the dynamics of human cultural evolution. However, few empirical studies have measured the importance of prestige relative to other effects, such as the content biases present within transmitted information. Here, we report the findings of an experimental transmission study designed to compare the simultaneous effects of a high- or low-prestige model with the presence of content containing social, survival, emotional, moral, rational, or counterintuitive information. Results from multimodel inference reveal that prestige is a significant factor in determining salience and recall, but that several content biases, specifically social, survival, negative emotional, and biological counterintuitive information, are significantly more influential. Further, we find evidence that prestige serves as a conditional learning strategy when no content cues are available. Our results demonstrate that content biases serve a vital and underappreciated role in cultural transmissionIntroduction Methods - Experimental protocol - Participants - Story production - Recordings - Data coding and transcription - Data analysis - Ethics statement Results - Sample demographics - Participants showed preferential recall of biased information - Content biases were more influential than prestige bias - Transmission biases explain little variance in recall Discussion - Prestige bias has a minor effect on transmission - Prestige is unconsciously employed as a secondary bias - Content biases have distinct effects - Narrative structural features may aid transmission - Implications for the understanding of transmissio

The spindle pole body of Schizosaccharomyces pombe enters and leaves the nuclear envelope as the cell cycle proceeds

This is the publisher's version, also available electronically from "http://www.molbiolcell.org".he cycle of spindle pole body (SPB) duplication, differentiation, and segregation in Schizosaccharomyces pombe is different from that in some other yeasts. Like the centrosome of vertebrate cells, the SPB of S. pombe spends most of interphase in the cytoplasm, immediately next to the nuclear envelope. Some gamma-tubulin is localized on the SPB, suggesting that it plays a role in the organization of interphase microtubules (MTs), and serial sections demonstrate that some interphase MTs end on or very near to the SPB. gamma-Tubulin is also found on osmiophilic material that lies near the inner surface of the nuclear envelope, immediately adjacent to the SPB, even though there are no MTs in the interphase nucleus. Apparently, the MT initiation activities of gamma-tubulin in S. pombe are regulated. The SPB duplicates in the cytoplasm during late G2 phase, and the two resulting structures are connected by a darkly staining bridge until the mitotic spindle forms. As the cell enters mitosis, the nuclear envelope invaginates beside the SPB, forming a pocket of cytoplasm that accumulates dark amorphous material. The nuclear envelope then opens to form a fenestra, and the duplicated SPB settles into it. Each part of the SPB initiates intranuclear MTs, and then the two structures separate to lie in distinct fenestrae as a bipolar spindle forms. Through metaphase, the SPBs remain in their fenestrae, bound to the polar ends of spindle MTs; at about this time, a small bundle of cytoplasmic MTs forms in association with each SPB. These MTs are situated with one end near to, but not on, the SPBs, and they project into the cytoplasm at an orientation that is oblique to the simple axis. As anaphase proceeds, the nuclear fenestrae close, and the SPBs are extruded back into the cytoplasm. These observations define new fields of enquiry about the control of SPB duplication and the dynamics of the nuclear envelope

The use of beta-D-glucanase as a substitute for Novozyme 234 in immunofluorescence and protoplasting

Novozym 234 has been used for many years to prepare protoplasts of Aspergillus nidulans and other fungi for transformation. It has also been very useful in immunofluorescence studies for partially digesting walls of fixed hyphae or germlings to allow antibodies to penetrate into the cytoplasm. In recent years, the availability of Novozym 234 has become problematic, and we have searched for combinations of available enzymes that are suitable for protoplasting and immunofluorescence studies in A. nidulans

Alanine-scanning mutagenesis of Aspergillus γ-tubulin yields diverse and novel phenotypes

This is the publisher's version, also available electronically from "www.molbiolcell.org".We have created 41 clustered charged-to-alanine scanning mutations of the mipA, γ-tubulin, gene of Aspergillus nidulans and have created strains carrying these mutations by two-step gene replacement and by a new procedure, heterokaryon gene replacement. Most mutant alleles confer a wild-type phenotype, but others are lethal or conditionally lethal. The conditionally lethal alleles exhibit a variety of phenotypes under restrictive conditions. Most have robust but highly abnormal mitotic spindles and some have abnormal cytoplasmic microtubule arrays. Two alleles appear to have reduced amounts of γ-tubulin at the spindle pole bodies and nucleation of spindle microtubule assembly may be partially inhibited. One allele inhibits germ tube formation. The cold sensitivity of two alleles is strongly suppressed by the antimicrotubule agents benomyl and nocodazole and a third allele is essentially dependent on these compounds for growth. Together our data indicate that γ-tubulin probably carries out functions essential to mitosis and organization of cytoplasmic microtubules in addition to its well-documented role in microtubule nucleation. We have also placed our mutations on a model of the structure of γ-tubulin and these data give a good initial indication of the functionally important regions of the molecule

A mutation in γ-tubulin alters microtubule dynamics and organization and is synthetically lethal with the kinesin-like protein Pkl1p

This is the publisher's version, also available electronically from "http://www.molbiolcell.org".Mitotic segregation of chromosomes requires spindle pole functions for microtubule nucleation, minus end organization, and regulation of dynamics. γ-Tubulin is essential for nucleation, and we now extend its role to these latter processes. We have characterized a mutation in γ-tubulin that results in cold-sensitive mitotic arrest with an elongated bipolar spindle but impaired anaphase A. At 30°C cytoplasmic microtubule arrays are abnormal and bundle into single larger arrays. Three-dimensional time-lapse video microscopy reveals that microtubule dynamics are altered. Localization of the mutant γ-tubulin is like the wild-type protein. Prediction of γ-tubulin structure indicates that non-α/β-tubulin protein–protein interactions could be affected. The kinesin-like protein (klp)Pkl1p localizes to the spindle poles and spindle and is essential for viability of the γ-tubulin mutant and in multicopy for normal cell morphology at 30°C. Localization and function of Pkl1p in the mutant appear unaltered, consistent with a redundant function for this protein in wild type. Our data indicate a broader role for γ-tubulin at spindle poles in regulating aspects of microtubule dynamics and organization. We propose that Pkl1p rescues an impaired function of γ-tubulin that involves non-tubulin protein–protein interactions, presumably with a second motor, MAP, or MTOC component