Regulation of LSD1 histone demethylase activity by its associated factors

LSD1 is a recently identified human lysine (K)-specific histone demethylase. LSD1 is associated with HDAC1/2; CoREST, a SANT domain-containing corepressor; and BHC80, a PHD domain-containing protein, among others. We show that CoREST endows LSD1 with the ability to demethylate nucleosomal substrates and that it protects LSD1 from proteasomal degradation in vivo. We find hyperacetylated nucleosomes less susceptible to CoREST/LSD1-mediated demethylation, suggesting that hypoacetylated nucleosomes may be the preferred physiological substrates. This raises the possibility that histone deacetylases and LSD1 may collaborate to generate a repressive chromatin environment. Consistent with this model, TSA treatment results in derepression of LSD1 target genes. While CoREST positively regulates LSD1 function, BHC80 inhibits CoREST/LSD1-mediated demethylation in vitro and may therefore confer negative regulation. Taken together, these findings suggest that LSD1-mediated histone demethylation is regulated dynamically in vivo. This is expected to have profound effects on gene expression under both physiological and pathological conditions.     

PtdIns(4,5)P2 functions at the cleavage furrow during cytokinesis

Phosphoinositides play important roles in regulating the cytoskeleton and vesicle trafficking, potentially important processes at the cleavage furrow. However, it remains unclear which, if any, of the phosphoinositides play a role during cytokinesis. A systematic analysis to determine if any of the phosphoinositides might be present or of functional importance at the cleavage furrow has not been published. Several studies hint at a possible role for one or more phosphoinositides at the cleavage furrow. The best of these are genetic data identifying mutations in phosphoinositide-modifying enzymes (a PtdIns(4)P-5-kinase in S. pombe and a PI-4-kinase in D. melanogaster) that interfere with cytokinesis. The genetic nature of these experiments leaves questions as to how direct may be their contribution to cytokinesis. Here we show that a single phosphoinositide, PtdIns(4,5)P2, specifically accumulates at the furrow. Interference with PtdIns(4,5)P2 interferes with adhesion of the plasma membrane to the contractile ring at the furrow. Finally, four distinct interventions to specifically interfere with PtdIns(4,5)P2 each impair cytokinesis. We conclude that PtdIns(4,5)P2 is present at the cleavage furrow and is required for normal cytokinesis at least in part because of a role in adhesion between the contractile ring and the plasma membrane.     

Acute ascorbate supplementation alone or combined with arginase inhibition augments reflex cutaneous vasodilation in aged human skin

Full expression of reflex cutaneous vasodilation (VD) is dependent on nitric oxide (NO) and is attenuated in older humans. NO may be decreased by an age-related increase in reactive oxygen species or a decrease in L-arginine availability via upregulated arginase. The purpose of this study was to determine the effect of acute antioxidant supplementation alone and combined with arginase inhibition on reflex VD in aged skin. Eleven young (Y; 22 +/- 1 yr) and 10 older (O; 68 +/- 1 yr) human subjects were instrumented with four intradermal microdialysis (MD) fibers. MD sites were control (Co), NO synthase inhibited (NOS-I), L-ascorbate supplemented (Asc), and Asc + arginase-inhibited (Asc + A-I). After baseline measurements, subjects underwent whole body heating to increase oral temperature (T(or)) by 0.8 degrees C. Red blood cell flux was measured by using laser-Doppler flowmetry, and cutaneous vascular conductance (CVC) was calculated (CVC = flux/mean arterial pressure) and normalized to maximal (CVC(max)). VD during heating was attenuated in O (Y: 37 +/- 3 vs. O: 28 +/- 3% CVC(max); P < 0.05). NOS-I decreased VD in both groups compared with Co (Y: 20 +/- 4; O: 15 +/- 2% CVC(max); P < 0.05 vs. Co within group). Asc and Asc + A-I increased VD beyond Co in O (Asc: 35 +/- 4% CVC(max); Asc + A-I: 41 +/- 3% CVC(max); P < 0.001) but not in Y (Asc: 36 +/- 3% CVC(max); Asc + A-I: 40 +/- 5% CVC(max); P > 0.05). Combined Asc + A-I resulted in a greater increase in VD than Asc alone in O (P = 0.001). Acute Asc supplementation increased reflex VD in aged skin. Asc combined with arginase inhibition resulted in a further increase in VD above Asc alone, effectively restoring CVC to the level of young subjects.     

Scale-dependent inhibition drives regular tussock spacing in a freshwater marsh

Regular spatial patterning is common in nature, and various mechanisms of self-organization have been proposed to explain regular patterning. We report on regular spatial patterning in Carex stricta in a freshwater wetland and investigate the applicability of theoretical models that explain regular patterning based on inhibition, facilitation, or interaction between the two. Spectral analysis of aerial photographs revealed that tussocks were regularly spaced at an average distance of 60 cm. Photosynthetically active radiation varied significantly with distance from the tussock and was lowest at intermediate distance from the tussock center (15-40 cm). Using transplants to assay growth conditions, we found that C. stricta grew well in all distance classes with and without natural C. stricta biomass, except at intermediate distances when buried in C. stricta wrack. Our experimental results reveal that C. stricta inhibits its growth in a scale-dependent manner: inhibition was found to peak at intermediate distance from the tussock. We compared three alternative models to examine potential mechanisms driving regularity and found that, similar to our experimental results, scale-dependent inhibition provides the best explanation for the observed regular tussock spacing. Our study underlines the importance of scale-dependent feedback in the formation of regular spatial patterning in ecosystems.     

The structural basis of cooperative regulation at an alternate genetic switch

Bacteriophage lambda is a paradigm for understanding the role of cooperativity in gene regulation. Comparison of the regulatory regions of lambda and the unrelated temperate bacteriophage 186 provides insight into alternate ways to assemble functional genetic switches. The structure of the C-terminal domain of the 186 repressor, determined at 2.7 A resolution, reveals an unusual heptamer of dimers, consistent with presented genetic studies. In addition, the structure of a cooperativity mutant of the full-length 186 repressor, identified by genetic screens, was solved to 1.95 A resolution. These structures provide a molecular basis for understanding lysogenic regulation in 186. Whereas the overall fold of the 186 and lambda repressor monomers is remarkably similar, the way the two repressors cooperatively assemble is quite different and explains in part the differences in their regulatory activity.     

Lis1 is an initiation factor for dynein-driven organelle transport

The molecular motor cytoplasmic dynein is responsible for most minus-end-directed, microtubule-based transport in eukaryotic cells. It is especially important in neurons, where defects in microtubule-based motility have been linked to neurological diseases. For example, lissencephaly is caused by mutations in the dynein-associated protein Lis1. In this paper, using the long, highly polarized hyphae of the filamentous fungus Aspergillus nidulans, we show that three morphologically and functionally distinct dynein cargos showed transport defects in the genetic absence of Lis1/nudF, raising the possibility that Lis1 is ubiquitously used for dynein-based transport. Surprisingly, both dynein and its cargo moved at normal speeds in the absence of Lis1 but with reduced frequency. Moreover, Lis1, unlike dynein and dynactin, was absent from moving dynein cargos, further suggesting that Lis1 is not required for dynein-based cargo motility once it has commenced. Based on these observations, we propose that Lis1 has a general role in initiating dynein-driven motility.