Proceedings of the 9th International Symposium on MDS and SAA in Childhood

2021 Molecular and Cellular Pediatrics  
Hematopoietic stem cells (HSC) are responsible for life-long maintenance and regeneration of the adult vertebrate blood system. The first HSCs arise from intra-aortic hematopoietic cluster cells (IAHC) in the mouse aorta at embryonic day (E)10.5 through a transdifferentiation process called endothelial-to-hematopoietic-transition (EHT). Gata2 is one of several transcription factors pivotal to the development of the adult hematopoietic system and is required for HSC generation in the embryo.
more » ... 2 -/mouse embryos suffer lethality at E10.5 and Gata2 +/-HSCs are qualitatively defective. Utilizing our Gata2Venus reporter mouse (Kaimakis et al., Blood, 2016) for time-lapse imaging of EHT in vivo, we found rapid pulsatile Gata2Venus expression level changes in single transitioning cells, implicating transcriptional instability during establishment of hematopoietic fate (Eich et al., J Exp Med, 2018). Flow cytometric analysis of IAHCs revealed cells with varying levels of Gata2Venus (V medium , V high ) expression. Bulk RNA sequencing of V med showed enrichment of genes involved in leukocyte extravasation, whereas V hi cells upregulated mature myeloid-type genes. Hematopoietic progenitors (HPC) were highly enriched in both fractions, and HSCs were exclusively in the V med fraction. Single cell RNAseq of IAHCs (CD31 + ckit + V med ) revealed surprising heterogeneity as represented by five distinct transcriptomic clusters (Vink et al., Cell Reports, 2020). Functional HSCs could be refined with SSC, CD27 and Ly6A phenotypic parameters in one major cluster to reveal the transcriptome of the first functional HSCs. Immunostaining of mouse embryos localized these HSCs to aortic clusters containing 1-2 cells. The very low frequency of HSCs in the IAHCs (1/600 amidst the 300/600 frequency of HPCs) highlights the complexity in programming HSC identity as defined by repopulating function, and raises the questionwhat processes influence acquisition of this rare HSC identity rather than the more abundant closely-related HPC or other identities? I will discuss these issues and the results of single cell methodologies that suggest a stochastic process of quantitative molecular states leading to the establishment of HSC fate/function. Hematopoietic Stem Cell Transplantation in Children and Adolescents with GATA2-Related Myelodysplastic Syndrome
doi:10.1186/s40348-021-00125-9 pmid:34633564 fatcat:7t2yntv7cbhqbiwjmqk7hxswxe