Reasoning Through Representations

Over the last two decades there has been increasing recognition of the central role played by multimodal representational practices as part of the disciplinary literacies through which students reason and learn in science. While there is recognition of the need for teachers to use, interpret and coordinate representational work in science classrooms there has been little research into the specific ways in which such work occurs to support quality learning, or how effective representational practices might be situated within different pedagogical traditions. This Chapter draws on close video ethnographic analysis of astronomy lessons in Australia, Germany and Taiwan, to investigate the representational coordination practices of competent teachers. The sequences were respectively six, five and 15 lessons long, each supported by significant digital and other representational resources. This representational work occurred within very different classroom organisational contexts, with disparate presumptions concerning the roles of teacher and students in constructing knowledge, different emphasis in assessment with Taiwan having a strong tradition of centralised competitive testing, and the greater focus on open group tasks in Australia and Germany. The study aimed to identify whether, within this contextual diversity, there are transcendent principles governing the way representations and models are established and coordinated. The research demonstrated the strategic ways in which the teachers established representational meaning, and used a range of narrative and embodied devices to establish meaning through coordination of sequences of representations

Clustering transmembrane-agrin induces filopodia-like processes on axons and dendrites

The transmembrane form of agrin (TM-agrin) is primarily expressed in the CNS, particularly on neurites. To analyze its function, we clustered TM-agrin on neurons using anti-agrin antibodies. On axons from the chick CNS and PNS as well as on axons and dendrites from mouse hippocampal neurons anti-agrin antibodies induced the dose- and time-dependent formation of numerous filopodia-like processes. The processes appeared within minutes after antibody addition and contained a complex cytoskeleton. Formation of processes required calcium, could be inhibited by cytochalasine D, but was not influenced by staurosporine, heparin or pervanadate. Time-lapse video microscopy revealed that the processes were dynamic and extended laterally along the entire length of the neuron. The lateral processes had growth cones at their tips that initially adhered to the substrate, but subsequently collapsed and were retracted. These data provide the first evidence for a specific role of TM-agrin in shaping the cytoskeleton of neurites in the developing nervous system