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International audience; Recent work has implicated the actin cytoskeleton in tissue size control and tumourigenesis, but how changes in actin dynamics contribute to hyperplastic growth is still unclear. Overexpression of Pico, the only Drosophila Mig-10/RIAM/Lamellipodin adapter protein family member, has been linked to tissue overgrowth via its effect on the myocardin-related transcription factor (Mrtf), an F-actin sensor capable of activating serum response factor (SRF). Transcriptional changes induced by acute Mrtf/SRF signalling have been largely linked to actin biosynthesis and cytoskeletal regulation. However, by RNA profiling, we find that the common response to chronic mrtf and pico overexpression in wing discs was upregulation of ribosome protein and mitochondrial genes, which are conserved targets for Mrtf/ SRF and are known growth drivers. Consistent with their ability to induce a common transcriptional response and activate SRF signalling in vitro, we found that both pico and mrtf stimulate expression of an SRF-responsive reporter gene in wing discs. In a functional genetic screen, we also identified deterin, which encodes Drosophila Survivin, as a putative Mrtf/SRF target that is necessary for pico-mediated tissue overgrowth by suppressing proliferation-associated cell death. Taken together, our findings raise the possibility that distinct targets of Mrtf/SRF may be transcriptionally induced depending on the duration of upstream signalling.

Background: Investigating the kinetics of Aβ peptide aggregation in vivo is vital to understanding Alzheimer disease. Results: Linking two Aβ40 or Aβ42 peptides together increases their aggregation rates in Drosophila, but only increases the neurotoxicity of Aβ42. Conclusion: Increasing the rate of aggregation of Aβ increases amyloid deposition but not necessarily toxicity. Significance: The toxicity of Aβ depends on the mechanism and not just the rate of amyloid formation., The generation and subsequent aggregation of amyloid β (Aβ) peptides play a crucial initiating role in the pathogenesis of Alzheimer disease (AD). The two main isoforms of these peptides have 40 (Aβ40) or 42 residues (Aβ42), the latter having a higher propensity to aggregate in vitro and being the main component of the plaques observed in vivo in AD patients. We have designed a series of tandem dimeric constructs of these Aβ peptides to probe the manner in which changes in the aggregation kinetics of Aβ affect its deposition and toxicity in a Drosophila melanogaster model system. The levels of insoluble aggregates were found to be substantially elevated in flies expressing the tandem constructs of both Aβ40 and Aβ42 compared with the equivalent monomeric peptides, consistent with the higher effective concentration, and hence increased aggregation rate, of the peptides in the tandem repeat. A unique feature of the Aβ42 constructs, however, is the appearance of high levels of soluble oligomeric aggregates and a corresponding dramatic increase in their in vivo toxicity. The toxic nature of the Aβ42 peptide in vivo can therefore be attributed to the higher kinetic stability of the oligomeric intermediate states that it populates relative to those of Aβ40 rather than simply to its higher rate of aggregation.

Publisher Summary This chapter focuses on highly efficient zebrafish transgenesis mediated by the meganuclease I-SceI. Fish are excellent candidates for the production of transgenics for two important reasons. First, fish represent the largest and most diverse group of vertebrates and provide an advantageous system for in vivo studies of developmental processes to gain knowledge of gene regulation and the action of gene products in vertebrates. Second, conventional selective breeding of fish for improved growth or other characteristics is a very slow process. Transgenic fish technology has the potential to improve genetic traits such as increased growth potential, disease resistance, improved feed conversion efficiency, or other desirable genetic traits for aquaculture in one generation. The establishment of methods for successful transgenesis is one of the basic criteria for an organism to be referred to as model organism. Several endonucleases (meganucleases) encoded by introns and inteins have been shown to promote homing (lateral transfer) of their respective genetic elements into intron- or inteinless homologous allelic sites. By introducing sitespecific double-strand breaks (DSBs) in intronless alleles, these nucleases create recombinogenic ends that engage in gene conversion, resulting in duplication of the intron. The I-SceI system has been used as a tool in mammalian cells and Drosophila. The meganuclease can also be used in fish for comparative studies of cis-acting regulatory elements and homologous recombination (HR). Meganuclease transgenesis as described in this chapter could be further improved, including insulators upstream and downstream of the DNA of interest to protect the transgene from the influences of heterochromatin and epigenetic control of surrounding genomic sequences.