Primary study on directed differentiation of embryonic stem cells into thyrocyte-like cells in vitro

Objective: To investigate the feasibility of directed differentiation of embryonic stem cells (ESCs) into thyrocyte-like cells in vitro. Methods: Murine E14 ESCs were cultured in methylcellulose semisolid medium to form embryoid bodies (EBs). These EBs were transferred for further inductive culture with the stepwise addition of growth factors (TSH, insulin and KI) into the culture medium. During differentiation, cell morphology was observed through phase contrast microscopy and compared with the normal thyroid cells from mouse. The molecular markers of thyroid cells were performed by indirect immunofluorescent analysis under fluorescent microscopy. Gene expressions of thyroid specific mRNA were analyzed by RT-PCR for molecules TSH receptor (TSHR), paired box gene 8 (PAX8), sodium iodide symporter (NIS), thyroid peroxidase (TPO) and thyroglobulin (Tg). Results: After EBs formation, on day six of further culture added with inductive factors TSH, insulin and KI, ESCs-derived cells expressed thyroid-specific genes such as PAX8, NIS, TPO, Tg and TSHR. On the 8th day, these ESCs-derived thyrocyte-like cells overexpressed TSHR, thyroid transcription factor-1 (TTF-1) whereas PAX8, thyroid transcription factor-2 (TTF-2) remained in a housekeeping level. On the 10th day, all the molecular markers (including TSHR, PAX8, NIS, TPO and Tg) were overexpressed. Morphology of these markers positive differentiated cells was similar to those normal thyroid cells. Conclusions: ESCs can differentiate into thyrocyte-like cells under certain inductive conditions and is possibly related to growth factors in vitro. This study suggests that a renewable source of thyroid follicular cells derived from ESCs holds great therapeutic potential for future cell replacement therapy in clinic. (authors)