There was decreased neuronal connectivity in SCZD hiPSC neurons (Fig. 2; SI Fig. 4B,C; SI Fig. 5,6). FACS analysis confirmed differences in neuronal connectivity and demonstrated that comparable numbers of βIII-tubulin-positive neurons were labeled with LV-SYNP-HTG. Though the mechanism of rabies trans-neuronal tracing is not fully understood, the presynaptic protein NCAM has been implicated10; NCAM expression is decreased in SCZD hiPSC neurons (SI Table 3). Rabies trans-neuronal tracing occurs in functionally immature hiPSC neurons (SI Fig. 4E) and in the presence of the voltage-gated sodium channel blocker tetrodotoxin (TTX) (1µM), depolarizing KCl (50mM) or the calcium channel blocker ryanodine (10µM) (SI Fig. 4F). Decreased trans-neuronal tracing is evidence of decreased neuronal connectivity, but not necessarily decreased synaptic function, in SCZD hiPSC neurons.
