Isolation of endo a cDNA from mouse 8-cell stage embryos

To analyse the species of genes expressed in a cleavage stage mouse embryo, we have constructed a cDNA library containing 3.0 × 10 5 independent clones from about 2 × 10 3 embryos at the 8-cell stage of development. Endo A cDNA prepared from parietal yolk sac endoderm like PYS-2 cells was used to screen the library. Southern blot analyses using the endo A sequence as a probe and restriction mapping analyses revealed that four independent recombinants had been inserted endo A sequence. Sequencing data of these clones showed that endo A mRNA present in the 8-cell stage embryo is identical to that of parietal yolk sac endoderm cells.