SEX-RELATED GROWTH-RATE DIFFERENCES IN MOUSE PREIMPLANTATION EMBRYOS IN-VIVO AND IN-VITRO

Sex-related growth rate differences in preimplantation mouse embryos w ere investigated. In experiment I, Day 3 embryos were recovered from r eproductive tracts, classified according to developmental stage, and c ultured for 24 hr in CZB medium containing glucose. Each embryo was th en reclassified and stained for measurement of number of nuclei and fi nally sexed using the polymerase chain reaction. In experiment II, Day 4 embryos were recovered, classified, stained, and sexed as in experi ment I immediately after recovery. Morphologically, there were no diff erences between the sexes in either of the experiments on Day 4. Howev er, based on number of nuclei, the data showed that in vitro condition s support the development of male embryos to the blastocyst stage comp ared to female embryos. Furthermore, growth rate differences were obse rved in vivo on Day 3, as females compacted earlier than males. These results suggest that the increased cell proliferation in cultured male embryos is an artifact caused by the in vitro environment. The variat ion may be due to sex differences in embryonal energy metabolism durin g the preimplantation stage. The growth difference implies different i n vitro requirements of male and female embryos. (C) 1995 Wiley-Liss, Inc.