Expression profiling by high throughput sequencing
In contrast to mouse, human female germ cells develop asynchronously. Germ cells transition to meiosis, erase genomic imprints, and reactivate the X chromosome. It is unknown if these events all appear asynchronously, and how they relate to each other. Here we combine exome sequencing of human fetal and maternal tissues with single-cell RNA-sequencing of five donors. We reconstruct full parental haplotypes and quantify changes in parental allele specific expression, genome-wide. First we distinguish PGC, pre-meiotic, and meiotic transcriptional stages. Next we demonstrate that germ cells from various stages monoallelically express imprinted genes from e.g. the SNURF-SNRPN cluster and confirm it by methylation patterns. Finally we show that ±30% of the PGCs, are still reactivating their inactive X chromosome and that this is related to transcriptional stage, and not to embryonic age. Altogether, we reveal the complexity and cell-to-cell heterogeneity of transcriptional and epigenetic remodelling in female human germ cells.
RNA sequences from human gonadal (N=73) and adrenal cells (N=35) from the mentioned fetuses 8.1-14.4wk of development (equivalent to 10.1-16.4 weeks of gestation) using SMART-seq2.