Directly Converted Human Fibroblasts Mature to Neurons and Show Long-Term Survival in Adult Rodent Hippocampus

Figure 3

iN cells with mature neuronal profile exhibit sparse synaptic integration. (a) Immunostaining of hippocampal slice with RFP-labelled iN grafts (on the left). Middle image shows higher magnification with the recorded iN cell, also identified by biocytin staining (on the right). (b) Continuous voltage clamp recording of grafted iN cell at −70 mV, showing sparse PSCs, with magnified insets (numbered 1 to 4). (c) Schematic explanation of optogenetic activation of ChR2-expressing host tissue, while recording from a grafted iN (left), or a ChR2-expressing host cell (right), for comparison; traces shown in (d–f). Blue light activation of ChR2-expressing host tissue does not result in synaptic response in the transplanted iN cells (left), neither in voltage-clamp mode, while applying blue light continuously for 10s (d) or as 1 ms paired pulses (e), nor in current-clamp mode (f), while there is a clear strong response to blue light in the host ChR2-expressing cells (d, e, right), with light-induced APs in current-clamp mode (f). Blue lines indicate the place and time of light application. Note the difference in scale in (d) traces between iN and host cells. Scale bars: (a) 100 μm; (b) 5 pA/1 s; (c) insets 2 pA/10 ms; (d) 50 pA/1 s (left) and 20 pA/1 s (right); (e) 20 pA/20 ms; and (f) 10 mV/10 ms.

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