This week in PNAS, researchers from New Jersey and Wisconsin say that palmitoylation controls the dynamics of heterochromatin in budding yeast via the telomere-binding protein Rif1. The posttranslational addition of palmitate to cysteines in eukaryotic cells anchors target proteins to membranes, the authors write. In this study, they show that "the Saccharomyces cerevisiae palmitoyltransferase Pfa4 enhanced heterochromatin formation at the cryptic mating-type loci HMR and HML via Rif1, a telomere regulatory protein." The team detected acylated Rif1 in extracts from wild-type cells, but not from pfa4∆ mutant cells. "Surprisingly, the pfa4∆ mutation had only mild effects on telomeric regulation, suggesting Rif1's roles at HM loci and telomeres were more complexly related than previously thought," the team adds.
Also in PNAS this week, US researchers present an approach for preventing UV-induced skin carcinogenesis, through genetic inhibition of the ataxia telangiectasia and Rad3-related kinase. The team generated transgenic mice with diminished ATR function in their skin, and crossed them into a UV-sensitive background. "These transgenic mice were viable and showed no histological abnormalities in skin. Primary keratinocytes from these mice had diminished UV-induced Chk1 phosphorylation and two-fold augmentation of apoptosis after UV exposure," the authors write. "With chronic UV treatment, transgenic mice remained tumor-free for significantly longer and had 69 percent fewer tumors at the end of observation of the full cohort, compared with littermate controls with the same genetic background." This suggests that the inhibition of replication checkpoint function can suppress skin carcinogenesis, and supports the inhibition of ATR as the relevant mechanism, the team adds.
Researchers at the University of North Carolina, Chapel Hill, present a combination therapy of shRNA knockdown and an optimized resistant transgene for diseases caused by misfolded proteins in PNAS this week. The team used alpha-1 antitrypsin deficiency with the piZZ mutant phenotype as a model system to determine the best way to silence the piZZ transcript and restore circulating wild-type AAT expression from resistant codon-optimized AAT transgene cassette. "After systemic injection of a self-complimentary AAV serotype 8 vector encoding shRNA in piZZ transgenic mice, both mutant AAT mRNA in the liver and defected serum protein level were inhibited by 95 percent, whereas liver pathology, as monitored by dPAS and fibrosis staining, reversed," the authors write. "The molecular approaches applied in this study can simultaneously prevent liver pathology and restore blood AAT concentration in AAT deficiencies."
Finally in PNAS this week, researchers in the US and Germany report that augmin promotes meiotic spindle formation and bipolarity in Xenopus egg extracts. The researchers used an assay system in which they could observe hundreds of meiotic spindles forming around chromatin-coated beads. "Spindles forming in augmin-depleted extracts showed reduced rates of microtubule formation and were predominantly multipolar, revealing a function of augmin in stabilizing the bipolar shape of the acentrosomal meiotic spindle," the authors write. "Our studies also have uncovered an apparent augmin-independent microtubule nucleation process from acentrosomal poles, which becomes increasingly active over time and appears to partially rescue the spindle defects that arise from augmin depletion."