Project description:Hematopoietic stem cell (HSC) differentiation into mature lineages has been studied under physiological conditions in vivo by genetic barcoding-driven lineage tracing. HSC clones differ in output (differentiation-inactive versus differentiation-active), and in fates (multilineage versus lineage-restricted). Single-cell sequencing data revealed transcriptome diversity of HSC and progenitors, and suggested differentiation pathways. However, molecular hallmarks of functionally distinct HSC clones have not been resolved because existing lineage tracing experiments did not provide transcriptomes, and single cell RNA sequencing lacked information on precursor-product relationships, and hence fate. To close this gap, here we introduce PolyloxExpress, a Cre recombinase-dependent DNA substrate for in situ barcoding in mice that is expressed as mRNA. PolyloxExpress barcoding allows parallel readout of clonal HSC fates (via comparison of barcodes in HSC and mature lineages), and transcriptomes (via single-cell RNA sequencing and barcode matching). Analysing a total of 91 individual HSC clones, we show that differentiation-inactive versus differentiation-active HSC clones reside in different regions of the transcriptional landscape. Inactive HSC clones are closer to the origin of the transcriptional trajectory, yet are proliferatively not more quiescent than active clones. Multilineage versus myelo-erythroid fate-restricted HSC clones show very few transcriptional differences at the HSC stage, yet pronounced fate-specific profiles at the multipotent progenitor stage. Projecting HSC clones with defined fates onto transcriptional landscapes provides a basis for future studies into the molecular determinants for stem cell fate.
Project description:Hematopoietic stem cell (HSC) differentiation into mature lineages has been studied under physiological conditions in vivo by genetic barcoding-driven lineage tracing. HSC clones differ in output (differentiation-inactive versus differentiation-active), and in fates (multilineage versus lineage-restricted). Single-cell sequencing data revealed transcriptome diversity of HSC and progenitors, and suggested differentiation pathways. However, molecular hallmarks of functionally distinct HSC clones have not been resolved because existing lineage tracing experiments did not provide transcriptomes, and single cell RNA sequencing lacked information on precursor-product relationships, and hence fate. To close this gap, here we introduce PolyloxExpress, a Cre recombinase-dependent DNA substrate for in situ barcoding in mice that is expressed as mRNA. PolyloxExpress barcoding allows parallel readout of clonal HSC fates (via comparison of barcodes in HSC and mature lineages), and transcriptomes (via single-cell RNA sequencing and barcode matching). Analysing a total of 91 individual HSC clones, we show that differentiation-inactive versus differentiation-active HSC clones reside in different regions of the transcriptional landscape. Inactive HSC clones are closer to the origin of the transcriptional trajectory, yet are proliferatively not more quiescent than active clones. Multilineage versus myelo-erythroid fate-restricted HSC clones show very few transcriptional differences at the HSC stage, yet pronounced fate-specific profiles at the multipotent progenitor stage. Projecting HSC clones with defined fates onto transcriptional landscapes provides a basis for future studies into the molecular determinants for stem cell fate.
Project description:Transcriptional profiling of hESCs differentiated towards an endodermal fate in chemically-defined media (3 days) compared to clones subjected to EOMES knockdown (via shRNA) under the same conditions.
Project description:Cell fate is established through coordinated gene expression programs in individual cells. Regulatory networks that include the Gata2 transcription factor play central roles in hematopoietic fate establishment. Whereas Gata2 is essential to the embryonic development and function of hematopoietic stem cells that form the adult hierarchy, little is known of the in vivo expression dynamics of Gata2 in single cells. Here we examine Gata2 expression in single aortic cells as they establish hematopoietic fate in Gata2Venus mouse embryos. Time-lapse imaging reveals rapid pulsatile level changes in Gata2 reporter expression in cells undergoing endothelial-to-hematopoietic-transition. Moreover, Gata2 reporter pulsatile expression is dramatically altered in Gata2+/- aortic cells, which undergo fewer transitions and are reduced in hematopoietic potential. Our novel finding of dynamic pulsatile expression of Gata2 suggests a highly unstable genetic state in single cells concomitant with their transition to hematopoietic fate. This reinforces the notion that threshold levels of Gata2 influence fate establishment and has implications for transcription factor-related hematologic dysfunctions.