Transdifferentiation and remodeling of post-embryonic C. elegans cells by a single transcription factor

Abstract

Terminally differentiated post-mitotic cells are generally considered irreversibly developmentally locked, i.e. incapable of being reprogrammed in vivo into entirely different cell types. We found that brief expression of a single transcription factor, the ELT-7 GATA factor, can convert the identity of fully differentiated, highly specialized non-endodermal cells of the pharynx into fully differentiated intestinal cells in intact larvae and adult Caenorhabditis elegans. Stable expression of intestine-specific molecular markers parallels loss of markers for the original differentiated pharynx state; hence, there is no apparent requirement for a dedifferentiated intermediate during the transdifferentiation process. Based on high-resolution morphological characteristics, the transdifferentiated cells become remodeled to resemble typical intestinal cells at the level of both the cell surface and internal organelles. Thus, post-mitotic cells, though terminally differentiated, remain plastic to transdifferentiation across germ layer lineage boundaries and can be remodeled to adopt the characteristics of a new cell identity without removal of inhibitory factors. Our findings establish a simple model to investigate how cell context influences forced transdifferentiation of mature cells.

Transorganogenesis and transdifferentiation in C. elegans are dependent on differentiated cell identity

“…As reported previously, we confirmed that END-1 is not capable of activating expression of late markers of intestine differentiation in the pharynx (Fig. 1B; Zhu et al, 1997; Zhu et al, 1998; Riddle et al, 2013). As ELT-7 is the smallest of the endoderm GATA factors, it was conceivable that either its size, or some unique structural characteristic, endows it with the ability to access promoters contained in otherwise inaccessible chromatin within differentiated cells.…”

“…We observed widespread ELT-2::GFP expression in most tissues as early as 4 h, as previously reported (Fig. 3; Riddle et al, 2013). IFB-2 expression is first observed in the pharynx 8–12 h after ectopic ELT-7 expression, and in the somatic gonad at approximately 12 h (Fig.…”

“…Positive cross-regulation between ELT-2 and ELT-7 appears to maintain expression of all intestine-expressed genes throughout development and adulthood (Maduro and Rothman, 2002; Maduro et al, 2005; Sommermann et al, 2010; Wiesenfahrt et al, 2016). We previously found that brief expression of ELT-7 via a ubiquitously activated heat-shock promoter reprograms differentiated post-mitotic pharyngeal cells into intestine-like cells at any stage of development (Riddle et al, 2013). As reported previously, we confirmed that END-1 is not capable of activating expression of late markers of intestine differentiation in the pharynx (Fig.…”

“…We observed IFB-2::CFP on the apical surface of pharyngeal cells within 24 h after brief ectopic ELT-7 expression at any developmental stage or adulthood, consistent with our previous observations of immunoreactive IFB-2 (Figs. 1C, 8D; Riddle et al, 2013). Unexpectedly, we found that when ELT-7 expression is activated at late postembryonic stages, IFB-2 is expressed in the mid-body of the worm, more broadly distributed than previously detected (as we had focused earlier on the head region of decapitated adults to allow for antibody penetration).…”

“…The timing of this “multipotentiality-to-commitment transition” (MCT), which normally occurs during mid-embryogenesis, can be extended somewhat by the removal of chromatin remodeling factors or Notch pathway components (Yuzyuk et al, 2009; Djabrayan et al, 2012); however, major regulators of germ layer identity are generally unable to reprogram cell identity after the MCT. We previously reported that brief expression of ELT-7, a GATA-type transcription factor that controls intestine differentiation (Sommermann et al, 2010), can promote transdifferentiation of cells of the neuromuscular pharynx into intestine-like cells at any time during development or in adulthood (Riddle et al, 2013). While this process results in cells with striking similarity to intestinal cells, they do not assemble into a gut-like organ and hence this process does not reflect transorganogenesis – the conversion of one developing organ type into another.…”