biorxiv.org/content/10.110… We developed a novel microfluidic isotachophoresis method (Ribo-ITP) to measure ribosome occupancy from ultra-low input samples including single cells. Here, we characterized transcriptome-wide ribosome occupancy during early mouse development. (1/6) Our high coverage data enabled the first analysis of allele-specific ribosome occupancy in mouse preimplantation development. We discovered gene-specific differences in the timing of engagement of paternal RNAs with ribosomes. (2/6)