IMITATION SWITCH is required for normal chromatin structure and gene repression in PRC2 target domains.

Polycomb Group (PcG) proteins are part of an epigenetic cell memory system that plays essential roles in multicellular development, stem cell biology, X chromosome inactivation, and cancer. In animals, plants, and many fungi, Polycomb Repressive Complex 2 (PRC2) catalyzes trimethylation of histone H3 lysine 27 (H3K27me3) to assemble transcriptionally repressed facultative heterochromatin. PRC2 is structurally and functionally conserved in the model fungus Neurospora crassa, and recent work in this organism has generated insights into PRC2 control and function. To identify components of the facultative heterochromatin pathway, we performed a targeted screen of Neurospora deletion strains lacking individual ATP-dependent chromatin remodeling enzymes. We found the Neurospora homolog of IMITATION SWITCH (ISW) is critical for normal transcriptional repression, nucleosome organization, and establishment of typical histone methylation patterns in facultative heterochromatin domains. We also found that stable interaction between PRC2 and chromatin depends on ISW. A functional ISW ATPase domain is required for gene repression and normal H3K27 methylation. ISW homologs interact with accessory proteins to form multiple complexes with distinct functions. Using proteomics and molecular approaches, we identified three distinct Neurospora ISW-containing complexes. A triple mutant lacking three ISW accessory factors and disrupting multiple ISW complexes led to widespread up-regulation of PRC2 target genes and altered H3K27 methylation patterns, similar to an ISW-deficient strain. Taken together, our data show that ISW is a key component of the facultative heterochromatin pathway in Neurospora, and that distinct ISW complexes perform an apparently overlapping role to regulate chromatin structure and gene repression at PRC2 target domains

Settler-Colonialism, Memoricide and Indigenous Toponymic Memory: The Appropriation of Palestinian Place Names by the Israeli State

Cartography, place-naming and state-sponsored explorations were central to the modern European conquest of the earth, empire building and settler-colonisation projects. Scholars often assume that place names provide clues to the historical and cultural heritage of places and regions. This article uses social memory theory to analyse the cultural politics of place-naming in Israel. Drawing on Maurice Halbwachs’ study of the construction of social memory by the Latin Crusaders and Christian medieval pilgrims, the article shows Zionists’ toponymic strategies in Palestine, their superimposition of Biblical and Talmudic toponyms was designed to erase the indigenous Palestinian and Arabo-Islamic heritage of the land. In the pre-Nakba period Zionist toponymic schemes utilised nineteenth century Western explorations of Biblical ‘names’ and ‘places’ and appropriated Palestinian toponyms. Following the ethnic cleansing of Palestine in 1948, the Israeli state, now in control of 78 percent of the land, accelerated its toponymic project and pursued methods whose main features were memoricide and erasure. Continuing into the post-1967 occupation, these colonial methods threaten the destruction of the diverse historical cultural heritage of the land

Genetic modification of the diarrhoeal pathogen <i>Cryptosporidium parvum</i>

Recent studies into the global causes of severe diarrhea in young children have identified the protozoan parasite Cryptosporidium as the second most important diarrheal pathogen after rotavirus(1–3). Diarrheal disease is estimated to be responsible for 10.5% of overall child mortality(4). Cryptosporidium is also an opportunistic pathogen in the context of HIV-AIDS and organ transplantation(5,6). There is no vaccine and only a single approved drug that provides no benefit for those in gravest danger, malnourished children and immunocompromised patients(7,8). Cryptosporidiosis drug and vaccine development is limited by the poor tractability of the parasite, which includes lack of continuous culture, facile animal models, and molecular genetic tools(3,9). Here we describe an experimental framework to genetically modify this important human pathogen. We establish and optimize transfection of C. parvum sporozoites in tissue culture. To isolate stable transgenics we develop a mouse model that delivers sporozoites directly into the intestine, a Cryptosporidium CRISPR/Cas9 system, and in vivo selection for aminoglycoside resistance. We derive reporter parasites suitable for in vitro and in vivo drug screening, and we evaluate the basis of drug susceptibility by gene knock out. We anticipate the ability to genetically engineer the parasite will be transformative for Cryptosporidium research. Genetic reporters will provide quantitative correlates for disease, cure and protection and the role of parasite genes in these processes is now open to rigorous investigation