Global absolute quantification reveals tight regulation of protein expression in single Xenopus eggs

Recent developments in genomic sequencing technology have enabled comprehensive transcriptome analyses of single cells. In contrast, single cell proteomics analyses have been restricted to targeted analyses, for example using flow cytometry with GFP fusions or mass cytometry. Here, we performed global absolute protein quantification of single Xenopus laevis eggs using mass spectrometry-based proteomics. We quantified over 5800 proteins, thus representing the largest single cell proteome that has been characterized to date. Absolute protein amounts in single eggs are highly comparable, thus indicating a tight regulation of global protein abundance. Comparison between the single-cell proteome and transcriptome reveal poor expression correlation. Finally, we identified 439 proteins that significantly change in abundance during early embryogenesis. Many of these proteins do not show regulation at the transcript level. Altogether, our data reveal that the transcriptome is a poor indicator of the proteome and that protein levels are tightly controlled in Xenopus leavis eggs. RNA-seq in Xenopus laevis of 5 replicates of both single eggs and single embryos.