Date Published: January 31, 2017
Publisher: Public Library of Science
Author(s): Hyun Woo Choi, Yean Ju Hong, Jong Soo Kim, Hyuk Song, Ssang Gu Cho, Hojae Bae, Changsung Kim, Sung June Byun, Jeong Tae Do, Elias T. Zambidis.
Like embryonic stem cells, induced pluripotent stem cells (iPSCs) can differentiate into all three germ layers in an in vitro system. Here, we developed a new technology for obtaining neural stem cells (NSCs) from iPSCs through chimera formation, in an in vivo environment. iPSCs contributed to the neural lineage in the chimera, which could be efficiently purified and directly cultured as NSCs in vitro. The iPSC-derived, in vivo-differentiated NSCs expressed NSC markers, and their gene-expression pattern more closely resembled that of fetal brain-derived NSCs than in vitro-differentiated NSCs. This system could be applied for differentiating pluripotent stem cells into specialized cell types whose differentiation protocols are not well established.
Pluripotent stem cells are currently considered a valuable resource for studying regenerative biology and medicine due to their tremendous differentiation potential into all cell types within the body. To be physiologically relevant, cells differentiated from pluripotent stem cells in vitro should behave very similarly to their in vivo counterparts in both molecular and functional terms. Therefore, developing proper protocols for differentiating pluripotent stem cells into specific cell types is a critical step for studying developmental biology and advancing applications to the clinical stage. For these purposes, long-term expandable somatic cell types have been derived from pluripotent stem cells, including embryonic stem cell (ESC)- or induced pluripotent stem cell (iPSC)-derived neural stem cells (NSCs) [1–3].
Here, we established in vivo differentiated NSCs (iPS-cNSCs) from iPSCs by chimera formation, which were similar to fetal brain-derived NSCs in terms of morphology and gene-expression patterns. These results indicated that iPSCs contributed to the neural lineage in chimeras (in vivo environment), which could be purified and then directly cultured as NSCs in vitro. NSCs established from iPSCs through in vitro and in vivo differentiation systems are very similar to fetal brain-derived NSCs, but NSCs differentiated from an in vivo system were slightly more similar to fetal brain-derived NSCs than in vitro-differentiated NSCs. Araki et al. (2013) used in vivo-differentiated somatic cells from iPSCs for transplantations. They transplanted skin cells, a type of in vivo-differentiated somatic cells, from the tails of chimeric mice and showed that the transplanted cells were sustained over 10 months, which exceeded the period in which in vitro-differentiated somatic cells were sustained post-transplantation . There is another useful approach for in vivo differentiation system. Specific cell types could be isolated from pluripotent stem cells through teratoma formation, which was based on the ideas of teratoma contained diverse cell types [20–22]. We also found that in vivo differentiation through teratoma formation could be used to differentiate PSCs into NSCs . Chimera-derived differentiated NSCs also were more similar to fetal brain-derived NSCs than to NSCs derived by in vitro differentiation. These results suggested that the differentiation environment influences gene expression in differentiated cells and could be a crucial factor determining the characteristics of the differentiated cells from iPSCs.