NEURAL DIFFERENTIATION OF RHESUS EMBRYONIC STEM-CELLS

Primate embryonic stem (ES) cells are capable of indefinite, undiffere ntiated proliferation and maintain the potential to differentiate to t rophoblast and derivatives of embryonic endoderm, mesoderm, and ectode rm. We previously reported that neural differentiation by rhesus ES ce lls in teratomas includes tissue with a remarkable resemblance to neur al tube (Thomson et al. 1995). Here we examine a series of markers inc luding a cell proliferation marker, neurofilament proteins, and glial fibrillary acidic protein (GFAP) in teratomas at 5, 6, 7, 9, and 12 we eks after rhesus ES cell transplantation into muscles of immunodeficie nt mice. All teratomas examined contained derivatives of all three emb ryonic germ layers. Neural differentiation included tissues resembling neural tube and embryonic ganglia, as well as individual dispersed ne urons, and brain-like gray matter. Tumours of all ages contained neuro ns and proliferating cells, indicated by staining for neurofilament su bunits and Ki67 antigens. Younger tumours contained no or few astrocyt es indicated by the absence of GFAP staining, but as these tumours dev eloped, there was an increase in astrocyte differentiation. The result s indicate that normal neural differentiation is recapitulated, in par t, by the differentiation of rhesus ES cells in teratomas. The differe ntiation of rhesus ES cells provides an important new model for unders tanding human neural differentiation.