3115 – GATA2A DETERMINES THE SURVIVAL AND HOMEOSTATIC LINEAGE OUTPUT OF HAEMATOPOIETIC STEM AND PROGENITOR CELLS

Abstract

The transcription factor Gata2 is key regulator of haematopoietic stem and progenitor cells (HSPCs) during embryonic development of vertebrates. We took advantage of a partial genome duplication in zebrafish that lead to the appearance of two Gata2 genes, Gata2a and Gata2b, to address how Gata2 programmes the haemogenic endothelium (HE) towards the HSPC cell fate. Through deletion of a conserved intronic enhancer (i4 enhancer) in the gata2a locus, we show that reducing gata2a levels in the endothelium leads to decreased expression of gata2b and runx1, thus demonstrating that Gata2a activity is required for HE programming in embryos. By contrast, loss of gata2b impaired cmyb expression in the HSPC population but did not affect HE programming, indicating that Gata2a programmes HE first and Gata2b modulates HSPC programming later. Single cell transcriptional profiling of the adult kidney marrow revealed that gata2a and gata2b are expressed in HSPCs, but in different subsets. Strikingly, homozygous Gata2a mutants are viable and fertile, but show hypocellularity in the marrow niche and neutropenia, resembling GATA2 deficiency syndrome in humans. Gata2a enhancer mutants show fewer HSPCs and a lineage skewing towards the erythroid and B cell fates at the expense of the neutrophilic and monocytic lineages. These differences are already detectable in HSPCs. In addition, myeloid lineages in gata2a enhancer mutants ectopically express B- and erythroid lineage markers and fail to express lineage-specific genes at wild type levels, suggesting that Gata2a activity in HSPCs initiates and maintains lineage commitment in haematopoietic cells.