Direct in vivo cellular reprogramming involves transition through discrete, non-pluripotent steps

Abstract

SUMMARYCells can change identity during normal development, in response to tissue damage or defined artificial treatments, or during disease processes such as cancer. Strikingly, not only the reprogramming of tissue cells to an embryonic stem cell-like state, but also the direct conversion from one cell type to another have been described. Direct cell type conversion could represent an alternative strategy for cellular therapies. However, little is known about the actual cellular steps undertaken by a cell as it changes its identity and their possible consequences for the organism. Using an in vivo single-cell system of natural direct reprogramming, in which a C. elegans rectal cell transforms into a motoneuron, we present an in-depth analysis of the cellular transformations involved. We found that the reprogrammed cell transits through intermediate states during direct in vivo reprogramming. We identified and characterised a mutant in the conserved COE transcription factor UNC-3 in which this cellular transformation is blocked. We determined that complete erasure of initial identity first takes place, followed by stepwise, unc-3-dependent, redifferentiation into a motoneuron. Furthermore, unlike in vitro induced reprogramming, reversion to a dedifferentiated identity does not lead to an increase in cellular potential in a natural, in vivo context. Our findings suggest that direct cell type conversion occurs via successive steps, and that dedifferentiation can occur in the absence of cell division. Furthermore, our results suggest that mechanisms are in place in vivo to restrict cell potential during reprogramming, a finding with important implications for regenerative medicine.

White matter tract and glial-associated changes in 5-hydroxymethylcytosine following chronic cerebral hypoperfusion

“…Interestingly, in vitro we observed significant increases in NG2 protein in mature oligodendrocytes subjected to an oxidative challenge. On the basis of previous studies (Matés et al, 2008;Shen et al, 2008b;Liu and Casaccia, 2010;Selvaraj et al, 2010;Gu et al, 2011;Richard et al, 2011;Doege et al, 2012) we believe that the observed up-regulation of this protein might be associated with active reprogramming of adult oligodendrocytes under pathological conditions. Future experimental work should elucidate the epigenetic phenomena governing potential reprogramming in oligodendrocytes in the injured CNS.…”

CCAAT/enhancer binding protein α (C/EBPα)-induced transdifferentiation of pre-B cells into macrophages involves no overt retrodifferentiation

“…In an interesting example of physiological transdifferentiation in Caenorhabditis elegans, in which a gut epithelial cell transforms into a neuron, the cell transits through an intermediate stage during which it completely erases its identity before redifferentiating into a motoneuron, in a mechanism that requires Uncoordinated family member 3 (unc-3) activity (9).…”

An intersectional gene regulatory strategy defines subclass diversity of C. elegans motor neurons

“…Since animals carrying the unc-3 null allele ( e151 ) displayed severe effects (100% penetrance) in terms of MN subclass-specific gene expression (Figure 2A–C), we took advantage of a hypomorphic unc-3 allele, fp8 (Richard et al, 2011). While this allele shows defects as strong as the null allele for the DA9- and VA12-specific marker genes, its effects on unc-129 (DA1-7 marker) and del-1 (VA1-VA11 marker) are milder, thereby enabling combined mutant analysis.…”