PRODUCTION OF MEDAKAFISH CHIMERAS FROM A STABLE EMBRYONIC STEM-CELL LINE

Embryonic stem (ES) cell lines provide a unique tool for introducing t argeted or random genetic alterations through gene replacement, insert ional mutagenesis, and gene addition because they offer the possibilit y for in vitro selection for the desired, but extremely rare, recombin ant genotypes, So far only mouse blastocyst embryos are known to have the competence to give rise to such ES cell lines, We recently have es tablished a stable cell line (Mes1) from blastulae of the medakafish ( Oryzias latipes) that shows all characteristics of mouse ES cells in v itro. Here, we demonstrate that Mes1 cells also have the competence fo r chimera formation; 90% of host blastulae transplanted with Mes1 cell s developed into chimeric fry. This high frequency was not compromised by cryostorage or DNA transfection of the donor cells. The Mes1 cells contributed to numerous organs derived from all three germ layers and differentiated into various types of functional cells, most readily o bservable in pigmented chimeras. These features suggest the possibilit y that Mes1 cells may be a fish equivalent of mouse ES cells and that medaka can be used as another system for the application of the ES cel l technology.