Gene Network Polymorphism Illuminates Loss and Retention of Novel RNAi Silencing Components in the Cryptococcus Pathogenic Species Complex.

RNAi is a ubiquitous pathway that serves central functions throughout eukaryotes, including maintenance of genome stability and repression of transposon expression and movement. However, a number of organisms have lost their RNAi pathways, including the model yeast Saccharomyces cerevisiae, the maize pathogen Ustilago maydis, the human pathogen Cryptococcus deuterogattii, and some human parasite pathogens, suggesting there may be adaptive benefits associated with both retention and loss of RNAi. By comparing the RNAi-deficient genome of the Pacific Northwest Outbreak C. deuterogattii strain R265 with the RNAi-proficient genomes of the Cryptococcus pathogenic species complex, we identified a set of conserved genes that were lost in R265 and all other C. deuterogattii isolates examined. Genetic and molecular analyses reveal several of these lost genes play roles in RNAi pathways. Four novel components were examined further. Znf3 (a zinc finger protein) and Qip1 (a homolog of N. crassa Qip) were found to be essential for RNAi, while Cpr2 (a constitutive pheromone receptor) and Fzc28 (a transcription factor) are involved in sex-induced but not mitosis-induced silencing. Our results demonstrate that the mitotic and sex-induced RNAi pathways rely on the same core components, but sex-induced silencing may be a more specific, highly induced variant that involves additional specialized or regulatory components. Our studies further illustrate how gene network polymorphisms involving known components of key cellular pathways can inform identification of novel elements and suggest that RNAi loss may have been a core event in the speciation of C. deuterogattii and possibly contributed to its pathogenic trajectory

New Learning and the Classification of Learning Environments in Secondary Education

Contains fulltext : 64692.pdf (publisher's version ) (Closed access)This article presents a new classification scheme for learning environments in secondary education, based on a review of recent literature on new learning and a review of existing classification schemes. This new classification scheme emphasizes new forms of learning and is organized around three main aspects of learning environments that may be assumed to influence such learning: (a) learning goals, (b) the division of teacher and learner roles, and (c) the roles of the learners in relation to each other. It is then argued that teachers might use this classification scheme to design and evaluate their own learning environments. In addition, the scheme provides a clear framework for a next generation of process–product research