Deciphering in vivo reprogramming using single cell RNA sequencing in the pancreas

The manipulation of cell fates through reprogramming is one of the most exciting advances in recent years. The most striking breakthrough in the field occurred when Yamanaka first illustrated the possibility to convert differentiated cells into pluripotent stem cells by the ectopic expression of four transcription factors, Oct4, Sox2, Klf4 and c-Myc or OSKM. Our laboratory has demonstrated that transient expression of these four Yamanaka factors leads to teratoma formation in mice indicative of in vivo reprogramming. We were interested in deciphering the intermediate events of de-differentiation induced by OSKM in vivo before reaching pluripotency. For this purpose, we focused on the pancreas which we found to be the organ with the highest reprogramming efficiency in vivo. To gain an insight into the cellular heterogeneity generated by OSKM activation in vivo, we performed single cell RNA sequencing of partially reprogrammed pancreas. We found that in vivo reprogramming leads to the loss of pancreatic acinar identity and the acquisition of an atypical tubular morphology different from normal pancreatic ducts or from the metaplastic ducts produced by pancreatitis. We were able to capture cells that have lost their acinar identity and they have acquired alternative cell fates. This analysis provide us with a list of markers characteristic of the intermediate stages of OSKM reprogramming.