To study cellular reprogramming in vivo, we developed a new system to understand the mechanisms of transcription factor (TF)-induced transdifferentiation (Td) in C. elegans. Using this system, mesodermally derived coelomocytes (CCs), which have scavenging and hepatic functions, can be reprogrammed into neuron- or intestine-like cells. First, we found that that the zinc finger TF CHE-1, which specifies the identity of salt-sensing ASE neurons in C. elegans, directly reprograms CCs into ASE neuron-like cells when overexpressed specifically in CCs. Notably, CCs not only start expressing the ASE neuron-specific reporter
gcy-5::gfp, but also show neuron-like cell morphogenesis, show pan-neuronal gene expression, and stain for the synaptic protein UNC-10 (Rim1 homolog). Second, ectopic expression of the intestinal fate-inducing GATA-type TF ELT-7, which specifies the intestinal fate, converts CCs into intestinal-like cells. Reprogrammed CCs express intestine-specific genes, immuno-stain for the intestine-specific protein IFB-2, and form a bona fide lumen, which produces microvilli. Reprogramming of CCs is accompanied by loss of CC gene expression and physiological functions as it is expected for faithful cell identity conversion. As the mechanisms which turn off the starting cell fate during reprogramming are generally not well understand, we will use CC reprogramming to address this issue in two ways. To analyze and characterize the chromatin regulators involved in CCs reprogramming, we performed a chromatin-specific RNAi screen for reprogramming enhancers and suppressors. We have identified several candidates which, when knocked down, enhance or suppress CC conversion and may play a role during Td. Interestingly, functional enrichment analysis indicates that our putative enhancers and suppressors participate in common complexes and epigenetic pathways. In addition, in order to understand whether TFs, which induce reprogramming, are also implicated in turning off the CC fate, we are currently performing CC-specific ChIP-seq to identify the DNA binding sites of TF CHE-1 and ELT-7 individually accompanied by transcriptome analysis. Comparison of the genomic binding patterns of both TFs might reveal common trajectories of CC fate shutdown upon reprogramming.