Chemical dynamics of triacetylene formation and implications to the synthesis of polyynes in Titan's atmosphere.

For the last four decades, the role of polyynes such as diacetylene (HCCCCH) and triacetylene (HCCCCCCH) in the chemical evolution of the atmosphere of Saturn's moon Titan has been a subject of vigorous research. These polyacetylenes are thought to serve as an UV radiation shield in planetary environments; thus, acting as prebiotic ozone, and are considered as important constituents of the visible haze layers on Titan. However, the underlying chemical processes that initiate the formation and control the growth of polyynes have been the least understood to date. Here, we present a combined experimental, theoretical, and modeling study on the synthesis of the polyyne triacetylene (HCCCCCCH) via the bimolecular gas phase reaction of the ethynyl radical (CCH) with diacetylene (HCCCCH). This elementary reaction is rapid, has no entrance barrier, and yields the triacetylene molecule via indirect scattering dynamics through complex formation in a single collision event. Photochemical models of Titan's atmosphere imply that triacetylene may serve as a building block to synthesize even more complex polyynes such as tetraacetylene (HCCCCCCCCH).

A size of approximately 1 au for the radio source Sgr A* at the centre of the Milky Way.

Although it is widely accepted that most galaxies have supermassive black holes at their centres, concrete proof has proved elusive. Sagittarius A* (Sgr A*), an extremely compact radio source at the centre of our Galaxy, is the best candidate for proof, because it is the closest. Previous very-long-baseline interferometry observations (at 7 mm wavelength) reported that Sgr A* is approximately 2 astronomical units (au) in size, but this is still larger than the 'shadow' (a remarkably dim inner region encircled by a bright ring) that should arise from general relativistic effects near the event horizon of the black hole. Moreover, the measured size is wavelength dependent. Here we report a radio image of Sgr A* at a wavelength of 3.5 mm, demonstrating that its size is approximately 1 au. When combined with the lower limit on its mass, the lower limit on the mass density is 6.5 x 10(21)M(o) pc(-3) (where M(o) is the solar mass), which provides strong evidence that Sgr A* is a supermassive black hole. The power-law relationship between wavelength and intrinsic size (size proportional, variantwavelength(1.09)) explicitly rules out explanations other than those emission models with stratified structure, which predict a smaller emitting region observed at a shorter radio wavelength.

Age and gender-dependent alternative splicing of P/Q-type calcium channel EF-hand.

Ca(v)2.1 Ca(2+) channels (P/Q-type), which participate in various key roles in the CNS by mediating calcium influx, are extensively spliced. One of its alternatively-spliced exons is 37, which forms part of the EF hand. The expression of exon 37a (EFa form), but not exon 37b (EFb form), confers the channel an activity-dependent enhancement of channel opening known as Ca(2+)-dependent facilitation (CDF). In this study, we analyzed the trend of EF hand splice variant distributions in mouse, rat and human brain tissues. We observed a developmental switch in rodents, as well as an age and gender bias in human brain tissues, suggestive of a possible role of these EF hand splice variants in neurophysiological specialization. A parallel study performed on rodent brains showed that the data drawn from human and rodent tissues may not necessarily correlate in the process of aging.

TSC1 loss synergizes with KRAS activation in lung cancer development in the mouse and confers rapamycin sensitivity.

Germline TSC1 or TSC2 mutations cause tuberous sclerosis complex (TSC), a hamartoma syndrome with lung involvement. To explore the potential interaction between TSC1 and KRAS activation in lung cancer, mice in which Tsc1 loss and Kras(G12D) expression occur in a small fraction of lung epithelial cells were generated. Mice with a combined Tsc1-Kras(G12D) mutation had dramatically reduced tumor latency (median survival: 11.6-15.6 weeks) in comparison with Kras(G12D) alone mutant mice (median survival: 27.5 weeks). Tsc1-Kras(G12D) tumors showed consistent activation of mTOR (mammalian target of rapamycin)C1 and responded to treatment with rapamycin, leading to significantly improved survival, whereas rapamycin had minor effects on cancers in Kras(G12D) alone mice. Loss of heterozygosity for TSC1 or TSC2 was found in 22% of 86 human lung cancer specimens. However, none of the 80 lung cancer lines studied showed evidence of the lack of expression of either TSC1 or TSC2 or a signaling pattern corresponding to complete loss. These data indicate that Tsc1 loss synergizes with the Kras mutation to enhance lung tumorigenesis in the mouse, but that this is a rare event in human lung cancer. Rapamycin may have unique benefit for patients with lung cancer, for whom the TSC1/TSC2 function is limited.

Rab8b and its interacting partner TRIP8b are involved in regulated secretion in AtT20 cells.

Rab proteins are a family of small GTPases that regulate intracellular vesicle traffic. Rab8b, because of its homology with Rab8, has been suggested to function in vesicle transport to the plasma membrane. Using the yeast two-hybrid system, we identified a Rab8b interacting clone, termed TRIP8b, from a rat brain cDNA library. The gene encodes a 66-kDa protein with homology to the peroxisomal targeting signal 1 receptor. The interaction between Rab8b and TRIP8b was further verified by in vitro binding assays and co-immunoprecipitation studies. Additional experiments with Rab8b mutants demonstrated that Rab8b requires a guanine nucleotide but not prenylation for its interaction with TRIP8b. Western immunoblot analysis showed that TRIP8b was primarily expressed in brain. Subcellular fractionation of AtT20 cells revealed that TRIP8b was present in both cytosolic and membrane fractions. To investigate the function of Rab8b and TRIP8b in secretion, we examined the release of ACTH from AtT20 cells. Results from stable cell lines expressing Rab8b or TRIP8b indicated that both proteins had a stimulatory effect on cAMP-induced secretion of ACTH. In summary, these data suggest that Rab8b and TRIP8b interact with each other and are involved in the regulated secretory pathway in AtT20 cells.