Abstract. We given an upper bound for the least dilatation arising from a pseudo-Anosov map of a closed surface of genus greater or equal to three.

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Zusammenfassung Schulpraktische Studien sollen als zentrale Lerngelegenheiten im Lehramtsstudium den Studierenden die Möglichkeit bieten, Praxiserfahrungen zu sammeln, Theorie mit Praxis zu verzahnen und ihre Berufswahlmotivation kritisch zu reflektieren. Bisherige Studien beschäftigten sich meist mit der Einschätzung subjektiver Kompetenzentwicklung und es gibt nur wenige Belege dafür, ob die Studierenden ihre Berufswahlmotivation im Verlauf der Praktika reflektieren und verändern. Diese Studie untersucht, wie stabil die motivationalen Orientierungen im Laufe des Integrierten Semesterpraktikums sind und welche Faktoren neben der reinen Praxiserfahrung eine Rolle für die möglichen Veränderungen spielen. Hierfür wurden 201 Studierende sowohl vor als auch nach ihrem Praktikum befragt. Die Ergebnisse der Strukturgleichungsmodellierungen zeigen, dass die Berufswahlmotive äußerst stabil sind und sich nur die Lehrerselbstwirksamkeit im Verlauf des Praktikums verändert. Die Untersuchung interindividueller Entwicklungsverläufe hat gezeigt, dass lediglich die Reflexionsgelegenheiten neben der reinen Praxiserfahrung einen kleinen positiven Effekt auf die Entwicklung der Lehrerselbstwirksamkeit aufweisen. K 368 M. Bauer et al. Schlüsselwörter Schulpraktische Studien · Berufswahlmotivation · Lehrerselbstwirksamkeit · Lehrerbildung · Längsschnittstudie · Strukturgleichungsmodellierung Analysis of the stability and variability of motivational beliefs of teacher candidates during their long-term internshipAbstract Pedagogical field experiences in teacher training programs provide important learning opportunities for pre-service teachers to obtain practical experiences in a working environment, which are supposed to enable them to link the theoretical skills to their practical ones, to develop professional competencies and to reflect on their own career-choice. While many studies focus on students' self-perception of competence, few studies have addressed the change of motivational beliefs and the students' reflection on their motivation for becoming teachers. This study investigates the stability and variability of the motivational beliefs of future teachers during their long-term internship and aims to identify the predictors of the development of these beliefs. In this study, 201 students were surveyed before and after their longterm internship. The findings from the structural equation modelling analyses reveal a high stability of motivational beliefs and suggest that (a) only students' selfefficacy increases during the pedagogical field experiences and (b) only the opportunities to reflect during the accompanying courses at the university have a small effect on the development of teacher self-efficacy.

Combinatorial signaling is key to instruct context-dependent cell behaviors. During embryonic development, adult homeostasis and disease, Bone Morphogenetic Proteins (BMPs) act as dimers to instruct specific cellular responses. BMP ligands can form both homo- or heterodimers; however, obtaining direct evidence of the endogenous localization and function of each form has proven challenging. Here, we make use of precise genome editing and direct protein manipulation via protein binders to dissect the existence and functional relevance of BMP homo- and heterodimers in the Drosophila wing imaginal disc. This approach revealed in situ the existence of Dpp (BMP2/4)/Gbb (BMP5/6/7/8) heterodimers. We found that Gbb, despite being produced by all the cells of the wing imaginal disc, is only secreted by the cells in which Dpp is expressed. Dpp and Gbb form a gradient of heterodimers whereas neither Dpp nor Gbb homodimers are evident under endogenous physiological conditions. We find that the formation of heterodimers is critical for obtaining optimal signaling and long-range BMP distribution in the developing wing. These results indicate that Dpp/Gbb heterodimers are the active signal required for epithelial patterning and growth.

Precise genome engineering is essential for both basic and applied research, permitting the manipulation of genes and gene products in predictable ways. The irruption of the CRISPR/Cas technology accelerated the speed and ease by which defined exogenous sequences are integrated into specific loci. To this day, a number of strategies permit gene manipulation. Nevertheless, knock-in generation in multicellular animals remains challenging, partially due to the complexity of insertion screening. Even when achieved, the analysis of protein localization can still be unfeasible in highly packed tissues, where spatial and temporal control of gene labeling would be ideal. Here, we propose an efficient method based on homology-directed repair (HDR) and single-strand annealing (SSA) repair pathways. In this method, HDR mediates the integration of a switchable cassette. Upon a subsequent CRISPR-triggered repair event, resolved by SSA, the cassette is seamlessly removed. By engineering the Hedgehog (Hh) pathway components, we demonstrated fast and robust knock-in generation with both fluorescent proteins and short protein tags in tandem. The use of homology arms as short as 30 base pairs further simplified and cheapened the process. In addition, SSA can be triggered in somatic cells, permitting conditional gene labeling in different tissues. Finally, to achieve conditional labeling and manipulation of proteins tagged with short protein tags, we have further developed a toolbox based on rational engineering and functionalization of the ALFA nanobody.