Parental Allele-Specific Protein Expression in Single Cells In Vivo

Abstract

Allelic expression from each parent-of-origin is important as a backup and to ensure that enough protein products of a gene are produced. Thus far, it is not known how each cell throughout a tissue differs in parental allele expression at the level of protein synthesis. Here, we measure the expression of the Ribosomal protein L13a (Rpl13a) from both parental alleles simultaneously in single cells in the living animal. We use genome-edited Drosophila that have a quantitative reporter of protein synthesis inserted into the endogenous Rpl13a locus. We find that individual cells can have large (>10-fold) differences in protein expression between the two parental alleles. Cells can produce protein from only one allele oftentimes, and time-lapse imaging of protein production from each parental allele in each cell showed that the imbalance in expression from one parental allele over the other can invert over time. One sentence summary: Parental allele-specific protein expression varies widely across cells and over time. Highlights: We used genome editing to insert a quantifiable protein translation reporter into the endogenous Ribosomal protein L13a gene and thus track the protein expression of both parental alleles simultaneously in every single cell in the awake animal. Cells can have a large difference in protein expression for one parental allele over the other, and this can invert over time, and can occur in clusters of cells within a tissue. We demonstrate the highly variable nature of heterozygous and homozygous definitions across single cells, and over time. Our study demonstrates a new paradigm that can be used to examine inherited epigenetic control of expression from a specific parent-of-origin allele across single clonal cells from a common progenitor in vivo .