Neural differentiation of rhesus embryonic stem cells.

Primate embryonic stem (ES) cells are capable of indefinite, undifferentiated proliferation and maintain the potential to differentiate to trophoblast and derivatives of embryonic endoderm, mesoderm, and ectoderm. We previously reported that neural differentiation by rhesus ES cells in teratomas includes tissue with a remarkable resemblance to neural tube (Thomson et al. 1995). Here we examine a series of markers including a cell proliferation marker, neurofilament proteins, and glial fibrillary acidic protein (GFAP) in teratomas at 5, 6, 7, 9, and 12 weeks after rhesus ES cell transplantation into muscles of immunodeficient mice. All teratomas examined contained derivatives of all three embryonic germ layers. Neural differentiation included tissues resembling neural tube and embryonic ganglia, as well as individual dispersed neurons, and brain-like gray matter. Tumours of all ages contained neurons and proliferating cells, indicated by staining for neurofilament subunits and Ki67 antigens. Younger tumours contained no or few astrocytes indicated by the absence of GFAP staining, but as these tumours developed, there was an increase in astrocyte differentiation. The results indicate that normal neural differentiation is recapitulated, in part, by the differentiation of rhesus ES cells in teratomas. The differentiation of rhesus ES cells provides an important new model for understanding human neural differentiation.