Functional role of high mobility group proteins 14 and 17 during early mouse development

Following fertilization, the embryo undergoes a sequence of precisely timed cleavage cycles to produce a blastocyst. The timing of these cycles likely depends in part on appropriate levels of gene activity. I have investigated whether high mobility group (HMG) proteins 14 and 17, which are associated with chromatin containing transcribed genes, are expressed in mouse embryos and are required to maintain normal early developmental timing. As assayed using RT-PCR, mRNAs encoding both HMG-14 and HMG-17 were present throughout preimplantation development to the blastocyst stage. By immunofluorescence, both proteins were detected in the nuclei of prophase I-arrested oocytes and embryos beginning at the 2-cell stage. To investigate their function, antisense oligonucleotides targeting the 5' end of each mRNA species were injected into 1-cell stage embryos which were then cultured to develop to the blastocyst stage. At the 2- and 4-cell stages, only weak nuclear immunofluorescence was observed; however, by the 8-cell stage, the staining pattern of injected embryos was indistinguishable from controls. Thus, the injected antisense oligonucleotides transiently depleted the cellular supply of HMG-14 and HMG-17. Furthermore, the embryos in which both HMG-14 and MAG-17 had been depleted progressed significantly more slowly through successive stages of preimplantation development, as compared with embryos in which the proteins were individually depleted or injected with nonsense oligonucleotides. Therefore, it can be concluded that depletion of HMG-14 and HMG-17 from embryonic chromatin transiently delays preimplantation development, demonstrating a crucial role for these proteins in maintaining the normal temporal coordination of development