The topology of chromatin-binding domains in the NuRD deacetylase complex

Class I histone deacetylase complexes play essential roles in many nuclear processes. Whilst they contain a common catalytic subunit, they have diverse modes of action determined by associated factors in the distinct complexes. The deacetylase module from the NuRD complex contains three protein domains that control the recruitment of chromatin to the deacetylase enzyme, HDAC1/2. Using biochemical approaches and cryo-electron microscopy, we have determined how three chromatin-binding domains (MTA1-BAH, MBD2/3 and RBBP4/7) are assembled in relation to the core complex so as to facilitate interaction of the complex with the genome. We observe a striking arrangement of the BAH domains suggesting a potential mechanism for binding to di-nucleosomes. We also find that the WD40 domains from RBBP4 are linked to the core with surprising flexibility that is likely important for chromatin engagement. A single MBD2 protein binds asymmetrically to the dimerisation interface of the complex. This symmetry mismatch explains the stoichiometry of the complex. Finally, our structures suggest how the holo-NuRD might assemble on a di-nucleosome substrate.     

Mycorrhizal preference promotes habitat invasion by a native Australian orchid: Microtis media

Background and Aims

Mycorrhizal specialization has been shown to limit recruitment capacity in orchids, but an increasing number of orchids are being documented as invasive or weed-like. The reasons for this proliferation were examined by investigating mycorrhizal fungi and edaphic correlates of Microtis media, an Australian terrestrial orchid that is an aggressive ecosystem and horticultural weed.

Methods

Molecular identification of fungi cultivated from M. media pelotons, symbiotic in vitro M. media seed germination assays, ex situ fungal baiting of M. media and co-occurring orchid taxa (Caladenia arenicola, Pterostylis sanguinea and Diuris magnifica) and soil physical and chemical analyses were undertaken.

Key Results

It was found that: (1) M. media associates with a broad taxonomic spectrum of mycobionts including Piriformospora indica, Sebacina vermifera, Tulasnella calospora and Ceratobasidium sp.; (2) germination efficacy of mycorrhizal isolates was greater for fungi isolated from plants in disturbed than in natural habitats; (3) a higher percentage of M. media seeds germinate than D. magnifica, P. sanguinea or C. arenicola seeds when incubated with soil from M. media roots; and (4) M. media–mycorrhizal fungal associations show an unusual breadth of habitat tolerance, especially for soil phosphorus (P) fertility.

Conclusions

The findings in M. media support the idea that invasive terrestrial orchids may associate with a diversity of fungi that are widespread and common, enhance seed germination in the host plant but not co-occurring orchid species and tolerate a range of habitats. These traits may provide the weedy orchid with a competitive advantage over co-occurring orchid species. If so, invasive orchids are likely to become more broadly distributed and increasingly colonize novel habitats.     

FDG PET scans as evaluation of clinical response to dendritic cell vaccination in patients with malignant melanoma

Background

Measurements of tumour metabolism by [18F]fluorodeoxyglucose positron emission tomography (FDG-PET) have been successfully applied to monitor tumour response after chemo- and chemo-radiotherapy and may not have the same limitations as other morphological imaging techniques. In this study it is investigated whether FDG-PET might add information on the efficacy of immune therapy.

Materials and methods

In a retrospective analysis data from patients with advanced progressive melanoma, treated with DC vaccinations and evaluated by PET/CT scans at baseline as well as after 6 vaccinations were analysed. If a patient achieved stable disease according to RECIST, additional vaccinations were given. The PET scans were evaluated according to EORTC guidelines.

Results

PET/CT scans from 13 patients were evaluated. According to RECIST 3 patients achieved stable disease and 10 patients progressed. Interestingly, when evaluated by PET scans 2 patients had partial metabolic response and 1 patient had complete metabolic response of the 2 index lesions even though a new lesion appeared simultaneously. Ten patients were seen to have stable or progressive metabolic disease.

Conclusion

By adding PET scans to the CT evaluation of patients treated with DC vaccines, a more detailed picture of the single lesions was found. This seems to improve the clinical evaluation of the treatment. The lack of correlation between the PET and CT scans suggests that some of the increases in target lesions seen in CT scans might be due to oedema or immune-infiltrates and not progression of the disease. Thus, further investigation into the contribution of PET scans to the evaluation of cancer immunotherapy is needed.     

A Matter of Balance: Role of Neurexin and Neuroligin at the Synapse

Neurexins and neuroligins are synaptic cell adhesion molecules. Neurexins are primary located on the presynaptic membrane, whereas neuroligins are strictly postsynaptic proteins. Since their discovery, the knowledge of neurexins and neuroligins has expanded, implicating them in various neuronal processes, including the differentiation, maturation, stabilization, and plasticity of both inhibitory and excitatory synapses. Here, we review the most recent results regarding the structure and function of these cell adhesion molecules.     

Pest management in Otago

Abstract

The Otago Regional Council could perhaps be renamed the Otago Rabbit Council. Some 35% of our budget—$8 million—goes annually towards dealing with rabbits, which certainly meet the definition of a pest (an animal which “disrupts management objectives” and lives at a population density exceeding “what society considers to be an acceptable level”). We can only hope that the day will come when we can, with confidence, say that the problem is being solved and when public and private financial inputs into rabbit control can be set at a far more reasonable level.     

Attenuated PLD1 association and signalling at the H452Y polymorphic form of the 5-HT2A receptor

The 5-HT_2A receptor (5-HT_2AR) is implicated in psychotropic changes within the central nervous system (CNS). A number of polymorphisms have been reported in the 5-HT_2AR gene; one of these results in a non-synonymous change, H452Y, in the carboxy-terminal tail of the receptor protein. The minor allele (9% occurrence) has been statistically associated with CNS dysfunction such as impaired memory processing and resistance to neuroleptic treatment in schizophrenic patients. We investigated the impact of H452Y mutation of the 5-HT_2AR expressed in COS7 cells on distinctly coupled intracellular signalling pathways from the receptor, focusing on the heterotrimeric G protein-independent phospholipase D (PLD) pathway, compared to the conventional Gq/11-linked phospholipase C (PLC) pathway. The H452Y mutation selectively attenuated PLD signalling, which as in the wild-type receptor, was mediated by a molecular complex involving PLD1 docked to the receptor's carboxy-terminal tail domain. Co-immunoprecipitation and GST-fusion protein experiments revealed that the H452Y mutation selectively reduced PLD1 binding to the receptor. Experiments with blocking peptides to mimic short sections of the 5-HT_2AR tail sequence revealed that the peptide spanning residue 452 strongly reduced PLD but not PLC responses of the receptor. Similar observations were made when assessing both PLD responses and PLD-dependent cellular proliferation elicited by activation of 5-HT_2ARs natively expressed in MCF-7 cells. Overall these findings indicate that the H452Y polymorphic variant of the 5-HT_2AR displays selective disruption of its PLD signalling pathway. This may potentially play a role in the CNS dysfunction associated with the H452Y allele of the 5-HT_2AR.     

Effects of wildfire, rainfall and region on desert lizard assemblages: the importance of multi-scale processes

Vertebrate populations are influenced by environmental processes that operate at a range of spatial and temporal scales. Wildfire is a disturbance that can affect vertebrate populations across large spatial scales, although vertebrate responses are frequently influenced by processes operating at smaller spatial scales such as topography, interspecific interactions and regional history. Here, we investigate the effects of a broad-scale wildfire on lizard assemblages in a desert region. We predicted that a rainfall gradient within the region affected by the wildfire would influence lizard responses to the fire by encouraging post-fire succession to proceed more rapidly in high-rainfall areas, and would be enabled in turn by more rapid vegetation recovery. To test our prediction, we censused lizards, measured rainfall, undertook vegetation surveys and sampled invertebrate abundance across burnt and unburnt habitat ecotones within three regional areas situated along a gradient of long-term annual rainfall. Lizard diversity was not affected by fire or region and lizard abundance was influenced only by region. Lizard assemblage composition was also only influenced by region, but this did not relate to differences in rainfall or habitat as we had predicted. Regional differences in lizard assemblages related instead to food availability. The observed differences also likely reflected regional differences in the strength of biotic interactions with predators and changes in land use. Our study shows that assemblage responses to a disturbance were not uniform within a large desert region and instead were influenced by other environmental processes operating simultaneously at multiple temporal and spatial scales.