Regulation of gene expression in the preimplantation mouse embryo: Temporal and spatial patterns of expression of the transcription factor Sp1

Activation of the embryonic genome during preimplantation mouse development entails a dramatic reprogramming of the pattern of gene expression. The complement of transcription factors that ave present in the early embryo and that must intrinsically be involved in this reprogramming is essentially uncharacterized. We and others have demonstrated that transcription factor Spl is present in the mouse oocyte and early cleavage stage preimplantation embryo. Due to Spl's prominent role in regulating the expression of a vast array of genes that ave involved in cell proliferation and differentiation, as well as in general housekeeping functions, we characterized the temporal and spatial patterns of Spl expression during preimplantation development. The relative abundance of Spl transcripts, as well as transcripts for the TATA box-binding protein TBP, decreases during oocyte maturation and reaches a minimum level in the two-cell stage, after which time the abundance of these transcripts increases progressively to the blastocyst stage. Immunoblotting experiments detect Spl species of M(r) = 95,000 and 105,000 at all stages of preimplantation development. The amount of Spl increases about 8-fold during preimplantation development, and an alpha-amanitin-insensitive increase is observed between G1 and G2 of the one-cell embryo; this increase may reflect the mobilization of a maternal Spl transcript. Immunocytochemical experiments also reveal a similar increase in the amount of Spl during preimplantation; the nuclear concentration of Spl is greater in the trophectoderm cells than in the inner cell mass cells. Finally, gel-shift experiments document an increase during preimplantation development of a DNA-binding activity that is likely due to Spl. These increases in the abundance of the Spl protein and an Spl-like DNA-binding activity parallel increases in the rate of transcription that occur during preimplantation development. (C) 1997 Wiiey-Liss, Inc.