Differential expression of laminin chain-specific mRNA transcripts during mouse preimplantation embryo development.

Laminin is the first extracellular matrix protein that has been shown to be synthesized in preimplantation mouse embryos. In the present study, chain-specific expression patterns of laminin mRNAs were examined by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). During preimplantation mouse embryo development, temporal expression patterns of laminin chain mRNAs were somewhat differential: B1 chain mRNA was first detectable at the late two-cell stage and its level was gradually increased by the blastocyst stage. In contrast, B2 and A chain mRNAs first appeared at the morula and blastocyst stages, respectively. At the blastocyst stage, all of the laminin chain mRNAs were highly detected compared to the earlier stages. When embryos were flushed at the morula stage and cultured in vitro, all laminin chain mRNA levels were decreased or not changed in the process of blastocoele expansion. In contrast, in the in vivo condition where embryos at different stages of blastocyst were flushed at different time points, laminin chain mRNA levels were increased as a function of blastocoele expansion. These changes in laminin mRNAs were parallel with its receptors such as integrin alpha 3 and alpha 6. 3-Isobutyl-1-methylxanthine (IBMX), which is known to be a potent activator of blastocoele expansion and regulates cAMP metabolism, upregulated laminin expression (except B1 chain) in blastocysts cultured in vitro. In vitro cultured embryos normally developed up to the late blastocyst, although their development was delayed compared with the in vivo condition where laminin gene expression was gradually increased as the blastocoele expanded. These results indicate that laminin expression may not be involved directly in the regulation of blastocoele expansion. The uterine environment enclosing the preimplantation embryos appears, therefore, to play an important role in the regulation of laminin gene expression during blastocyst development.