STELLA and MuERV-L activation are essential for early mouse development

The maternal-to-zygotic transition (MZT) marks the period when the embryonic genome is activated and acquires control of development. Maternally inherited factors play a key role in this critical developmental process, which occurs at the 2-cell stage in mice. Here we investigated the function of the maternally inherited factor STELLA (DPPA3) using single-cell/embryo approaches. This submission concerns itself with transcriptional profiling of wild type and Stella knockout (Stella-/-) oocytes, wild type and Stella maternal/zygotic knockout (StellaM/Z-/-) 1-cell and 2-cell embryos. We show that loss of maternal STELLA results in widespread transcriptional mis-regulation and a partial failure of MZT. Strikingly, activation of the LTR class of transposable elements (TE), and particularly 2-cell specific MuERV-L elements, is significantly impaired in StellaM/Z-/- embryos, which leads to a failure to upregulate selected chimeric transcripts. We propose that STELLA is involved in ensuring activation of TEs that themselves play a key role during early development, in part through regulating embryonic gene expression.