We describe here the isolation and maintenance of pluripotent embryonic stem (ES) cells from equine blastocysts that have been frozen and thawed. Equine ES cells appear to main-tain a normal diploid karyotype in culture. These cells express markers that are characteris-tic of mouse ES cells, namely, alkaline phosphatase, stage-specific-embryonic antigen 1, STAT3, and Oct4. We also describe protocols for the induction of differentiation in vitro to neural precursor cells in the presence of basic fibroblast growth factor (bFGF), epidermal growth factor, and platelet-derived growth factor and to hematopoietic and endothelial cell lineages in the presence of bFGF, stem cell factor, and oncostatin M. Equine ES cells pro-vide a powerful tool for gene targeting and the generation of transgenic clonal offspring.
