Neural differentiation of mouse embryonic stem cells in chemically defined medium.

Directed differentiation of embryonic stem (ES) cells has enormous potential to derive a wide variety of defined cell populations of therapeutic value. To achieve this, it is necessary to use protocols that promote cell differentiation under defined culture conditions. Furthermore, understanding the mechanisms of cell differentiation in vitro will allow the development of rationale approaches to systematically manipulate cell fates. Here we have analysed the differentiation of mouse ES cells to the neural lineage under serum and feeder cell-free conditions, using a previously described chemically defined medium (CDM). In CDM, ES cell differentiation is highly neurogenic. Cell differentiation was monitored by analysis of a gene expression array (Clontech-Atlas) and by semi-quantitative RT-PCR for a panel of genes involved in cell lineage specification and patterning of the epiblast. In addition to expression of neural markers, data identified a transient expression of several genes associated with the organising activities of the embryonic node and visceral endoderm, including regulators of WNT, BMP, Hedgehog and FGF signaling pathways. Neural differentiation in CDM does not occur by a simple default mechanism, but was dependent on endogenous FGF signaling, and could be blocked by adding BMP4, and LiCl to simulate WNT activation. Neural differentiation was also inhibited by antagonising endogenous hedgehog activity. Taken together the profile of gene expression changes seen in CDM cultures recapitulates those seen in the early embryo, and is suggestive of common developmental mechanisms.