Spartan Daily November 20, 2012

Volume 139, Issue 44https://scholarworks.sjsu.edu/spartandaily/1360/thumbnail.jp

Pressure effects on the thermal stability of SiC fibers

Commercially available polymer derived SiC fibers were treated at temperatures from 1000 to 2200 C in vacuum and argon gas pressure of 1 and 1360 atm. Effects of gas pressure on the thermal stability of the fibers were determined through property comparison between the pressure treated fibers and vacuum treated fibers. Investigation of the thermal stability included studies of the fiber microstructure, weight loss, grain growth, and tensile strength. The 1360 atm argon gas treatment was found to shift the onset of fiber weight loss from 1200 to above 1500 C. Grain growth and tensile strength degradation were correlated with weight loss and were thus also inhibited by high pressure treatments. Additional heat treatment in 1 atm argon of the fibers initially treated at 1360 atm argon caused further weight loss and tensile strength degradation, thus indicating that high pressure inert gas conditions would be effective only in delaying fiber strength degradation. However, if the high gas pressure could be maintained throughout composite fabrication, then the composites could be processed at higher temperatures

Letter from Members of the Hiroshima YMCA to Geraldine Ferraro

Letter from members of the Hiroshima YMCA to Geraldine Ferraro. The authors invite Ferraro to visit the Atomic Bomb Museum in Hiroshima. A letter from Laurence M. Wiig of the YMCA International Institute for Peace is enclosed.https://ir.lawnet.fordham.edu/vice_presidential_campaign_correspondence_1984_international/1360/thumbnail.jp

Ectopic assembly of heterochromatin in Drosophila melanogaster triggered by transposable elements

A persistent question in biology is how cis-acting sequence elements influence trans-acting factors and the local chromatin environment to modulate gene expression. We reported previously that the DNA transposon 1360 can enhance silencing of a reporter in a heterochromatic domain of Drosophila melanogaster. We have now generated a collection of variegating phiC31 landing-pad insertion lines containing 1360 and a heat-shock protein 70 (hsp70)-driven white reporter to explore the mechanism of 1360-sensitive silencing. Many 1360-sensitive sites were identified, some in apparently euchromatic domains, although all are close to heterochromatic masses. One such site (line 1198; insertion near the base of chromosome arm 2L) has been investigated in detail. ChIP analysis shows 1360-dependent Heterochromatin Protein 1a (HP1a) accumulation at this otherwise euchromatic site. The phiC31 landing pad system allows different 1360 constructs to be swapped with the full-length element at the same genomic site to identify the sequences that mediate 1360-sensitive silencing. Short deletions over sites with homology to PIWI-interacting RNAs (piRNAs) are sufficient to compromise 1360-sensitive silencing. Similar results were obtained on replacing 1360 with Invader4 (a retrotransposon), suggesting that this phenomenon likely applies to a broader set of transposable elements. Our results suggest a model in which piRNA sequence elements behave as cis-acting targets for heterochromatin assembly, likely in the early embryo, where piRNA pathway components are abundant, with the heterochromatic state subsequently propagated by chromatin modifiers present in somatic tissue

Physical Structure of Planetary Nebulae. III. The Large and Evolved NGC 1360

NGC 1360 is a large planetary nebula (PN) without an obvious shell morphology. We have analyzed H-alpha images and high-dispersion echelle spectra of NGC 1360 in order to construct spatio-kinematic models and to determine its density distribution. The best-fit model indicates that NGC 1360 is a prolate ellipsoidal shell whose major axis is twice as long as its minor axis and is tilted by 60 arcdeg with respect to the line of sight. The large kinematic age of the shell, ~10,000 yr, and the low density of the nebula, <130 H-atom cm^-3, imply that NGC 1360 is an evolved PN and has begun to merge with the interstellar medium. The observed morphology and surface brightness profiles of NGC 1360 can be described well as a thick shell with a Gaussian radial density profile without a sharp inner edge, indicating a lack of on-going compression by a fast stellar wind. The FLIERs observed in NGC 1360 near the end of its major axis expand faster and are younger than the nebular shell.Comment: 5 pages, 5 figure

Reply to Hagen & Sudarshan's Comment

We show that the argument in Phys Rev Lett 70 (1993) 1360 is correct and consistent, and that Hagen & Sudarshan's solution has inconsistency leading to non-vanishing commutators of $[P^1, P^2]$ and $[P^j, H]$ even in physical states. This proves that many of HS's statements in their Comment are based merely on incorrect guess, but not on careful algebra.Comment: one page, UMN-TH-1245/9

Targets of Heterochromatin Assembly in Drosophila melanogaster

Heterochromatin is classically defined as densely staining regions of the genome; these domains are typically late replicating and show little recombination. Correct assembly of heterochromatin is critical for chromosome stability. Assembly begins with histone deacetylation and H3 lysine 9 di- and trimethylation: H3K9me2/3); the methylated H3 is typically bound by Heterochromatin Protein 1a: HP1a). Heterochromatin predominates at pericentric and telomeric domains --regions abundant in transposable elements: TEs) and satellite repeats. Transcription of these TEs has been found to generate a platform for assembly of heterochromatin through RNAi in S. pombe and A. thaliana, and may play a critical role in Drosophila melanogaster. However, the precise role of RNAi in heterochromatin assembly for a metazoan system such as flies remains unclear. However, 1360, a DNA transposable element in D. melanogaster, has been found to be sufficient to promote heterochromatin assembly in a repeat-rich region, as shown by a variegating phenotype of a hsp70-white reporter. RNAi components and heterochromatin factors such as HP1a were both implicated in this 1360-sensitive variegation, a form of position effect variegation: PEV). Here, I sought to determine the extent and mechanism of TE-sensitive PEV. A collection of 1360-sensitive landing pad insertion lines containing the hsp70-w reporter was generated. This tool allows for the repeated sampling of altered 1360 constructs in a variety of chromatin contexts, a useful a platform to study the attributes of 1360-sensitive variegation as well as PEV generally. We found 1360-sensitive PEV to extend to sites outside of annotated heterochromatin, although most sensitive sites lie within or proximal to heterochromatic masses. I used biochemical approaches to show that 1360-sensitive PEV corresponds to HP1a accumulation over the hsp70-w promoter region, confirming that the silencing is due to heterochromatin assembly. The deletion of sites within the 1360 element with homology to the PIWI-interacting RNAs: piRNAs) in 1360 suppressed PEV, as did dominant mutations in PIWI domain proteins. Similar results were obtained using Invader4, a retrotransposon, in the same landing pad site. The results support a mechanism that uses piRNAs for transposon-sensitive HP1a-silencing, likely early in development, with persistent effects observed in the adult somatic tissue of the eye. To determine if the sequence determinants required for 1360-sensitive silencing in a euchromatic region: as seen above) also operate in a repetitious sequence environment, where interspersed signals may operate cooperatively, I investigated a 1360-sensitive site in the piRNA generating locus 42AB. We find that mutations in piwi, along with many prototypical Su(var) mutations, result in weak suppression of variegation at this site, while an ago2 mutation enhances variegation. Tests of various fragments of the TEs do not reveal a strong dependency on piRNA matching sequences, contrary to the euchromatic site driven to a heterochromatic form by the added TE. These findings indicate that suppression of PEV by mutations in the genes for RNAi components occurs in a limited number of heterochromatic domains, predominantly those near gene clusters - sites typically found at the border between euchromatin and heterochromatin. Thus chromosomal context appears to be an important determinant for RNAi-dependent 1360-sensitive PEV. This finding helps to reconcile reports of inconsistent PEV effects from mutations in RNAi components that have been carried out using reporters in different domains. Collectively, these results indicate the TEs can act as sequence determinants of heterochromatin assembly at a subset of genomic sites using an RNAi-mediated targeting mechanism

General Education Subcommittee Minutes, October 22, 2013

Course Approvals Course/Designation Removals Syllabi Approvals Business USU 1300, 1320 and 1360 criteria discussions Proposed changes to the web pages and criteria for USU 1300, 1320 and 1360 Volunteer to chair and serve on the Social Sciences subcommittee Logan Campus Freshmen enrollment only down by 130 Next Meetin