Specificity protein 1 (SP1) plays an essential role in early bovine embryo development

A previous RNA-Seq study revealed that the transcript abundance of specificity protein 1 (SP1) was significantly higher in Day 7 bovine blastocysts compared to conceptuses on Days 10, 13, 16, and 19, suggesting a stage-specific role in early bovine embryo development. The present study aimed to characterize the mRNA expression of SP1 and associated candidate genes (ACSS1, C1QBP, ATF3, MAT2A, and POLD1) during early bovine embryo development from the 2-cell to blastocyst stage. Further, the effects of SP1 inhibition on embryo development were evaluated by culturing embryos with the SP1 inhibitor, mithramycin A (MT) at varying concentrations (0, 25, 50, 100, and 1000 nM). As further validation, we examined expression of SP1 and associated genes by interrogating transcriptomic data from Day 4 (16-cell stage) embryos cultured in vitro or in vivo in the oviducts of lactating or nonlactating dairy cows. The relative abundance of SP1 peaked at the time of embryonic genome activation, being higher (P < 0.05) in 8- and 16-cell embryos compared to the 2-cell stage, and decreasing thereafter (at the morula and blastocyst stages). Similarly, transcript abundance for most of the selected candidate genes involved in the SP1 network were upregulated (P < 0.05) at the 8- and 16-cell stage, but not at other stages investigated. Inhibition of SP1 with MT did not affect embryo development up to the 8-cell stage but reduced (P < 0.05) the proportion of embryos reaching the 16-cell and blastocyst stages in a dose-dependent manner. Moreover, blastocysts produced in the presence of MT contained fewer (P < 0.05) cells than blastocysts developed without MT. Expression of SP1 and associated genes in 16-cell stage (Day 4) embryos produced either in vitro or in vivo was higher (P < 0.05) compared to in vitro-produced 2- to 4- cell stage (Day 2) embryos. These findings suggest an essential role of SP1 during early embryo development, particularly around the time of embryonic genomic activation.