There is preliminary evidence that implantation of primary fetal striatal cells provides functional
benefit in patients with Huntington’s disease, a neurodegenerative condition resulting in loss of
medium-sized spiny neurons (MSN) of the striatum. Scarcity of primary fetal tissue means it is
important to identify a renewable source of cells from which to derive donor MSNs. Embryonic stem
(ES) cells, which predominantly default to telencephalic-like precursors in chemically defined
medium (CDM), offer a potentially inexhaustible supply of cells capable of generating the desired
neurons. Using an ES cell line, with the forebrain marker FoxG1 tagged to the LacZ reporter, we
assessed effects of known developmental factors on the yield of forebrain-like precursor cells in
CDM suspension culture. Addition of FGF2, but not DKK1, increased the proportion of FoxG1-
expressing cells at day 8 of neural induction. Oct4 was expressed at day 8, but was undetectable by
day 16. Differentiation of day 16 precursors generated GABA-expressing neurons, with few
DARPP32 positive MSNs. Transplantation of day 8 precursor cells into quinolinic acid-lesioned striata
resulted in generation of teratomas. However, transplantation of day 16 precursors yielded grafts
expressing neuronal markers including NeuN, calbindin and parvalbumin, but no DARPP32 6 weeks
post-transplantation. Manipulation of fate of ES cells requires optimization of both concentration
and timing of addition of factors to culture systems to generate the desired phenotypes.
Furthermore, we highlight the value of increasing the precursor phase of ES cell suspension culture
when directing differentiation toward forebrain fate, so as to dramatically reduce the risk of
teratoma formation
