Combinatorial genetics for conditional transgene activation allows studying gene function with temporal and tissue specific control like the Gal4-UAS system, which has enabled sophisticated genetic studies in Drosophila . Recently this system was adapted for zebrafish and promising applications have been introduced. Here, we report a systematic optimization of zebrafish Gal4-UAS genetics by establishing an optimized Gal4-activator (KalTA4). We provide quantitative data for KalTA4-mediated transgene activation in dependence of UAS copy numbers to allow for studying dosage effects of transgene expression. Employing a Tol2 transposon-mediated KalTA4 enhancer trap screen biased for central nervous system expression, we present a collection of self-reporting red fluorescent KalTA4 activator strains. These strains reliably transactivate UAS-dependent transgenes and can be rendered homozygous. Furthermore, we have characterized the transactivation kinetics of tissue-specific KalTA4 activation, which led to the development of a self-maintaining effector strain “Kaloop.” This strain relates transient KalTA4 expression during embryogenesis via a KalTA4-mediated autoregulatory mechanism to live adult structures. We demonstrate its use by showing that the secondary octaval nucleus in the adult hindbrain is likely derived from egr2b -expressing cells in rhombomere 5 during stages of early embryogenesis. These data demonstrate prolonged and maintained expression by Kalooping, a technique that can be used for permanent spatiotemporal genetic fate mapping and targeted transgene expression in zebrafish.

Our aging society is confronted with a dramatic increase of patients suffering from tauopathies, which include Alzheimer disease and certain frontotemporal dementias. These disorders are characterized by typical neuropathological lesions including hyperphosphorylation and subsequent aggregation of TAU protein and neuronal cell death. Currently, no mechanism-based cures are available. We generated fluorescently labeled TAU transgenic zebrafish, which rapidly recapitulated key pathological features of tauopathies, including phosphorylation and conformational changes of human TAU protein, tangle formation, neuronal and behavioral disturbances, and cell death. Due to their optical transparency and small size, zebrafish larvae are well suited for both in vivo imaging and drug development. TAU-induced neuronal cell death was imaged by time-lapse microscopy in vivo. Furthermore, we used this zebrafish model to identify compounds targeting the TAU kinase glycogen synthase kinase 3β (GSK3β). We identified a newly developed highly active GSK3β inhibitor, AR-534, by rational drug design. AR-534 reduced TAU phosphorylation in TAU transgenic zebrafish. This transgenic zebrafish model may become a valuable tool for further studies of the neuropathology of dementia.