Differential Effects of Delta1 and Jagged1 in Early Human Myelopoiesis: Correlation with Distinct Gene-Expression Profiles in CD34⁺ Cells.

The Notch ligands Delta1 and Jagged1 are known to differentially affect the development of B and T-cell lineages but their function in the myelopoiesis is still unclear. Here we show that Delta1 and Jagged1, expressed by bone-marrow-derived stromal cells, differentially affect de myeloid development of human CD34⁺ cells: Jagged1 increases their clonogenic potential both at the level of bi- (CFU-GM) and uni-potent progenitors (CFU-G and CFU-M), without quantitatively affecting terminal cell differentiation; Delta1 strikingly reduces the number of CFU-GM and differentiated monocytic cells.

Gene expression profiling of CD34⁺ cells cultured in contact with Jagged1 or Delta1, reveals that the observed phenotypic/functional differences correlate with the emergence of distinct transcription profiles for genes related to hematopoietic-differentiation programs, receptors for growth-factors and Notch-signalling.

The comparative analysis of different CD34⁺ sub-populations revealed that: cells with similar phenotypes (CD34⁺CD7⁻), but emerging in distinct environments (Delta1 or Jagged1), have different “lineage-specific” transcription profiles, Delta1-CD34⁺ cells exhibiting an almost “pure” myeloid program, whereas Jagged1-CD34⁺ cells are enriched in transcripts for B- and myeloid lineages; the same environment (Delta1) originates CD34⁺ cells with different phenotypes, as to CD7 expression, which differ in their lineage-specific transcription profiles: Delta1-CD34⁺CD7⁺ cells show a high expression of T/NK-cell related genes in contrast with their CD7⁻ counterparts which express a myeloid-lineage program. Furthermore, Jagged1 and Delta1-stromas have differential effects in the expression of genes coding for receptors for several hematopoietic growth factors. Overall, these transcription profiles agree with the specific cell-lineage-affiliation of the corresponding CD34⁺ cell sub-population. Quantitative analysis of transcripts from Notch-signalling-related genes in different CD34⁺ sub-populations showed that cells with similar phenotypes (CD34⁺CD7⁻), but emerging in distinct environments (Delta1 or Jagged1), have different expression profiles of receptors and targets of Notch. In the case of Delta1 environment, we observe a predominance of Notch3 and Hes1 transcripts, whereas Jagged1-CD34⁺ cells are enriched in Notch1 and Deltex transcripts. In the same stromal environment (Delta1) but different in CD34⁺ cell sub-populations Notch3 receptor was up-regulated. Delta1, contrary to Jagged1, promotes up-regulation of modulators of Notch signaling.

Together, the data show that Delta1 and Jagged1 modulate gene-expression programs in CD34⁺ cells in ways that contribute not only to cell-lineage-affiliation but also to the functional interactions between developing cells and their micro-environment.