TEMPORAL CONTROL OF GAP JUNCTION ASSEMBLY IN PREIMPLANTATION MOUSE EMBRYOS

The de novo assembly of gap junctions during compaction in the 8-cell stage of mouse development is a temporally regulated event. We have pe rformed experiments designed to explore the relationship between this event and DNA replication in the second, third, and fourth cell cycles after fertilization, Inhibition of DNA synthesis by continuous treatm ent with the DNA synthesis inhibitor, aphidicolin, during the third an d fourth cell cycles had no effect on the establishment of gap junctio nal coupling during compaction, However, a delay of 10 hours in DNA sy nthesis during the second cell cycle caused by a transient aphidicolin treatment resulted in the failure of gap junctional coupling at the t ime of compaction, Thus the timing of establishment of gap junctional coupling, like the timing of compaction itself, is linked to DNA repli cation in the 2-cell stage, Immunofluorescence analysis showed that th e failure of gap junctional coupling after aphidicolin treatment in th e 2-cell stage is correlated with the failure of nascent connexin43 to be inserted into plasma membranes. We propose that the developmental 'clock' that controls gap junction assembly is set in motion by events surrounding the second cycle of DNA replication, and that this 'clock ' ultimately controls the post-translational processing of connexin43.