Cell Biol Int 2018 May 20;42(5):608-614. Epub 2018 Feb 20.
Graduate School of Science and Engineering, Iwate University, 4-3-5, Ueda, Iwate Prefecture, 020-8551, Morioka, Japan.
The introduction of four key transcriptional factors (CRX, RAX, NEURO-D, OTX2) allows the direct differentiation of fibroblasts to retinal photoreceptor cells. This reprogramming was achieved with a combination of mono-cistronic viruses. Although the combination of mono-cistronic viruses was useful, a relatively high titer of recombinant viruses was necessary because co-infections are required. To overcome this issue, we established a poly-cistronic expression system for direct reprogramming and analyzed the biological characteristics of introduced cells after the exogenous introduction. The coding region of four reprogramming factors and EGFP (CRX, RAX, NEURO-D, OTX2, and EGFP; CNROE) was inserted into multiple sites of the pMYs-IP retrovirus or CSII-CMV lentivirus vector. The recombinant viruses were exposed to HE16 human embryonic fibroblasts. The expression levels of cone related genes were detected with real-time PCR. We detected the activation of two of the photoreceptor-related genes after the poly-cistronic expression of CRX, RAX, NEURO-D, and OTX2, but the rest of the genes did not exhibit transcriptional elevation. We concluded that the poly-cistronic expression of CNROE induced partial reprogramming into photoreceptor cells. We hypothesize that the direct reprogramming into photoreceptor cells might require relatively high protein expression levels of transcriptional factors.