A Refined Single Cell Landscape of Haematopoiesis in the Mouse Foetal Liver.

During prenatal life, the foetal liver is colonised by several waves of haematopoietic progenitors to act as the main haematopoietic organ. Single cell (sc) RNA-seq has been used to identify foetal liver cell types via their transcriptomic signature and to compare gene expression patterns as haematopoietic development proceeds. To obtain a refined single cell landscape of haematopoiesis in the foetal liver, we have generated a scRNA-seq dataset from a whole mouse E12.5 liver that includes a larger number of cells than prior datasets at this stage and was obtained without cell type preselection to include all liver cell populations. We combined mining of this dataset with that of previously published datasets at other developmental stages to follow transcriptional dynamics as well as the cell cycle state of developing haematopoietic lineages. Our findings corroborate several prior reports on the timing of liver colonisation by haematopoietic progenitors and the emergence of differentiated lineages and provide further molecular characterisation of each cell population. Extending these findings, we demonstrate the existence of a foetal intermediate haemoglobin profile in the mouse, similar to that previously identified in humans, and a previously unidentified population of primitive erythroid cells in the foetal liver.