Generation of embryonic stem cell lines from mouse blastocysts developed in vivo and in vitro: relation to Oct-4 expression.

Embryonic stem (ES) cells are the source of all embryonic germ layer tissues. Oct-4 is essential for their pluripotency. Since in vitro culture may influence Oct-4 expression, we investigated to what extent blastocysts cultured in vitro from the zygote stage are capable of expressing Oct-4 and generating ES cell lines. We compared in vivo with in vitro derived blastocysts from B6D2 mice with regard to Oct-4 expression in inner cell mass (ICM) outgrowths and blastocysts. ES cells were characterized by immunostaining for alkaline phosphatase (ALP), stage-specific embryonic antigen-1 (SSEA-1) and Oct-4. Embryoid bodies were made to evaluate the ES cells' differentiation potential. ICM outgrowths were immunostained for Oct-4 after 6 days in culture. A quantitative real-time PCR assay was performed on individual blastocysts. Of the in vitro derived blastocysts, 17% gave rise to ES cells vs 38% of the in vivo blastocysts. Six-day old outgrowths from in vivo developed blastocysts expressed Oct-4 in 55% of the cases vs 31% of the in vitro derived blastocysts. The amount of Oct-4 mRNA was significantly higher for freshly collected in vivo blastocysts compared to in vitro cultured blastocysts. In vitro cultured mouse blastocysts retain the capacity to express Oct-4 and to generate ES cells, be it to a lower level than in vivo blastocysts.