生命科学联合中心
题目：Classifying and mapping retinal neuronal circuits.
时间：2015-7-16（周四），13:00-13:20pm
Understanding a circuit requires defining its components and mapping their connections. For neural circuits, this corresponds to classifying neuronal subtypes and probing their synaptic connections. In this talk, I will illustrate how we do this in the retina. The first part of my talk focuses on how we classify a subgroup of neurons called alpha retinal ganglion cells (RGCs). We found that mouse line Kcng4-YFP labels alpha RGCs, which have large soma and dendritic fields and can be recognized by an antibody against neurofilaments (SMI32). Recording from these cells followed by morphological reconstruction showed that they comprised all three subtypes reported previously -On sustained, Off sustained and Off transient- plus a rare new subtype, On transient. We further sought molecular markers for alpha RGCs using transcriptomic approaches and examined a few of them. One of them called Osteopontin (OPN) is highly and only expressed in alpha RGCs. Finally, we showed that alpha RGCs regenerate preferentially following optic nerve injury and that OPN can promote this regeneration. Thus, our work revealed a new molecular marker for alpha RGCs, which is potentially a new agent to promote axon regeneration.
In the second part of my talk, I will describe a molecular tool developed to map electrical synaptic connections from genetically defined neuronal subtypes, making use of a dipeptide transporter Pept2. Cells expressing Pept2 (in a Cre-dependent way) take up a gap junction permeable fluorescent dipeptide, which then diffuses and labels coupled cells. I tested this method in cell culture and validated it in mouse retina using AAV carrying Pept2. In addition, this method allows us to study modulation of electrical synaptic connections. By applying this method, I found electrical synaptic connection between retinal horizontal cells is modulated by global light condition across the whole retina instead of local condition.
题目：Rewiring perisomatic inhibition by direct lineage reprogramming of neocortical projection neurons.
时间：2015-7-16（周四），13:20-13:40pm
During development of the cerebral cortex, GABAergic inhibitory interneurons recognize and pair with excitatory projection neurons to ensure the fine excitatory-inhibitory balance essential for proper local circuit function. Whether projection neuron identity has a role in the establishment of afferent inhibitory synapses is unknown. We report that direct in vivo lineage reprogramming of layer 2/3 (L2/3) callosal projection neurons (CPNs) into induced corticofugal projection neurons (iCFuPNs) increases functional inhibitory input onto the converted neurons to levels similar to endogenous CFuPNs of layer 5 (L5). iCFuPNs recruit increased numbers of inhibitory perisomatic synapses from parvalbumin (PV)-positive interneurons with single-neuron resolution and despite their ectopic location in L2/3. The data demonstrate that excitatory projection neurons affect local inhibition by extrinsically modulating afferent input by local interneurons and that reprogramming projection neuron class-specific identity can actively rewire the cortical microcircuit.
