Genome-wide association study on 13,167 individuals identifies regulators of blood CD34+ cell levels

Gata2 noncoding genetic variation as a determinant of hematopoietic stem/progenitor cell mobilization efficiency

Germline genetic variants alter the coding and enhancer sequences of GATA2, which encodes a master regulator of hematopoiesis. The conserved murine Gata2 enhancer (+9.5) promotes hematopoietic stem cell (HSC) genesis during embryogenesis. Heterozygosity for a single-nucleotide Ets motif variant in the human enhancer creates a bone marrow failure and acute myeloid leukemia predisposition termed GATA2 deficiency syndrome. The homozygous murine variant attenuates chemotherapy- and transplantation-induced hematopoietic regeneration, hematopoietic stem and progenitor cell (HSPC) response to inflammation, and HSPC mobilization with the therapeutic mobilizer granulocyte colony-stimulating factor (G-CSF). Because a Gata2 +9.5 variant attenuated G-CSF-induced HSPC expansion and mobilization, and HSC transplantation therapies require efficacious mobilization, we tested whether variation affects mechanistically distinct mobilizers or only those operating through select pathways. In addition to affecting G-CSF activity, Gata2 variation compromised IL-8/CXCR2- and VLA-4/VCAM1-induced mobilization. Although the variation did not disrupt HSPC mobilization mediated by plerixafor, which functions through CXCR4/CXCL12, homozygous and heterozygous variation attenuated mobilization efficacy of the clinically used plerixafor/G-CSF combination. The influence of noncoding variation on HSPC mobilization efficacy and function is important clinically because comprehensive noncoding variation is not commonly analyzed in patients. Furthermore, our mobilization-defective system offers unique utility for elucidating fundamental HSPC mechanisms.

Inference of cell type-specific gene regulatory networks on cell lineages from single cell omic datasets

Cell type-specific gene expression patterns are outputs of transcriptional gene regulatory networks (GRNs) that connect transcription factors and signaling proteins to target genes. Single-cell technologies such as single cell RNA-sequencing (scRNA-seq) and single cell Assay for Transposase-Accessible Chromatin using sequencing (scATAC-seq), can examine cell-type specific gene regulation at unprecedented detail. However, current approaches to infer cell type-specific GRNs are limited in their ability to integrate scRNA-seq and scATAC-seq measurements and to model network dynamics on a cell lineage. To address this challenge, we have developed single-cell Multi-Task Network Inference (scMTNI), a multi-task learning framework to infer the GRN for each cell type on a lineage from scRNA-seq and scATAC-seq data. Using simulated and real datasets, we show that scMTNI is a broadly applicable framework for linear and branching lineages that accurately infers GRN dynamics and identifies key regulators of fate transitions for diverse processes such as cellular reprogramming and differentiation.

Germline-somatic JAK2 interactions are associated with clonal expansion in myelofibrosis

Myelofibrosis is a rare myeloproliferative neoplasm (MPN) with high risk for progression to acute myeloid leukemia. Our integrated genomic analysis of up to 933 myelofibrosis cases identifies 6 germline susceptibility loci, 4 of which overlap with previously identified MPN loci. Virtual karyotyping identifies high frequencies of mosaic chromosomal alterations (mCAs), with enrichment at myelofibrosis GWAS susceptibility loci and recurrently somatically mutated MPN genes (e.g., JAK2). We replicate prior MPN associations showing germline variation at the 9p24.1 risk haplotype confers elevated risk of acquiring JAK2^V617F mutations, demonstrating with long-read sequencing that this relationship occurs in cis. We also describe recurrent 9p24.1 large mCAs that selectively retained JAK2^V617F mutations. Germline variation associated with longer telomeres is associated with increased myelofibrosis risk. Myelofibrosis cases with high-frequency JAK2 mCAs have marked reductions in measured telomere length – suggesting a relationship between telomere biology and myelofibrosis clonal expansion. Our results advance understanding of the germline-somatic interaction at JAK2 and implicate mCAs involving JAK2 as strong promoters of clonal expansion of those mutated clones.

Myelofibrosis is a risk factor for the development of Acute Myeloid Leukaemia. Here, the authors carry out an integrated genomic investigation of 933 myelofibrosis patients, and identified interactions between germline and somatic variation in patients who required haematopoietic cell transplantation.