GERM-LINE CONTRIBUTION OF EMBRYONIC STEM-CELLS IN CHIMERIC MICE - INFLUENCE OF KARYOTYPE AND IN-VITRO DIFFERENTIATION ABILITY

The effect of the karyotype and the ability to differentiate in vitro upon germ-line transmission by A3-1 embryonic stem (ES) cells in chime ric mice were examined. Germline transmission was confirmed in ES cell s exhibiting 38% and more of the normal karyotype, but no chimeric mic e and/or germ-line transmitters were observed regardless of the karyot ype when the cystic embryoid body (CEB) was formed on day 8 and later in the suspension culture. Germ-line transmission of the ES cells was not significantly influenced by formation of the simple embryoid body (SEE). Germ-line transmitters were preferentially observed in chimeras when the ES cell contribution to coat color was markedly increased, b ut this contribution to coat color varied regardless of the karyotype or in vitro differentiation ability. These results suggest that A3-1 E S cells which exhibit CEB at 7 days after suspension culture and appro ximately 40% of normal karyotype are capable of germ-line transmission in chimeric mice.