Identification of Quantitative Genetic Variations Regulating Hematopoietic Regeneration

Slow hematopoietic recovery following irradiation can result in adverse complications for many patients, but the genetic basis of recovery is ill defined. Using a zebrafish model of irradiation-induced hematopoietic regeneration, we defined differences in recovery between two commonly used wild type strains (AB and Wik) and mapped quantitative trait loci (QTL) that govern these differences. Regeneration was assayed by measuring the frequency of multilineage precursors, which are the earliest hematopoietic population detectable following irradiation injury in the zebrafish. Wik fish had a higher precursor frequency (mean-35) at 7 days post irradiation (dpi) than AB fish (mean-30) indicating Wik regenerate faster. To establish the genetic determinant underlying the difference in hematopoietic regeneration, AB and Wik fish were crossed to generate F2 ABXWik hybrid animals for mapping. The F2 animals displayed a range of precursor frequencies from 4.5 to 52.9 at 7dpi. Interval mapping was performed on the fish with the 10% highest and lowest precursor frequency. Initial mapping performed with over 200 single nucleotide polymorphisms distributed across the genome indicated significant linkage on Chromosome 3 (LOD-3.258), which was then confirmed by analyses in F3 progeny. Whole genome sequencing was employed to further refine the genetic interval to a 20 Mbp region. The genes within this QTL (136) were then compared to 132 genes found in a mouse QTL (Scp2) on Chromosome 11 associated with differences between HSC proliferation in C57/Bl6 and DBA.2 mice. Four out of the 12 common genes tested displayed differential gene expression between AB and Wik fish, suggesting that variable expression in multiple genes likely contribute to fluctuations in regeneration. This study is one of the first to use zebrafish genetics to define factors that control natural fluctuations in regenerative potential and can provide targets for therapies to boost hematopoietic output during times of stress.