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Ectopic Expression of Nup98-HoxA10 Augments Erythroid Differentiation of Human Embryonic Stem Cells



From the April 2011 Issue of Stem Cells

Paper Commentary by Stuart P. Atkinson

HOX genes are a group of related genes that act to determine the basic structure and orientation of an organism and contain a DNA-binding domain called the homeodomain which can bind to enhancer sequences of other genes to control their transcription. Many HOX genes are expressed in human primitive haematopoietic stem and progenitor cells but have also been identified as fusion partners in leukaemia’s. One of the most common fusion partners for HOX genes is NUP98 (Slape and Aplan), a nucleoporin protein which is part of the nuclear pore complex (NPC). NA10 is an artificially engineered fusion of the NUP98 gene and the homeodomain of HOXA10, a key regulator of primitive hematopoietic cell expansion and erythroid/megakaryocytic lineage choice (Magnusson et al) and has been shown to potently stimulate the in vitro expansion of murine haematopoietic stem cells (HSCs) (Ohta et al). Given this action of NA10, researchers in the lab of Mickie Bhatia at the Stem Cell and Cancer Research Institute at McMaster University decided to investigate the role of NA10 in regulating early haematopoiesis from human embryonic stem cells (hESCs), a study now presented (Ji et al.) in the April Edition of Stem Cells.

Initial analysis of embryoid body (EB)-mediated hematopoietic differentiation of NA10-transduced hESCs demonstrated that control and transduced cells were similar with regards to their production of CD45+ mature hematopoietic cells, but at day 15 an increase in erythropoiesis was observed in the transduced cells. However, the ability of NA10-transduced cells to differentiate into other blood cell types remained unaffected. Next, the effect of NA10 was studied in hESC-derived hemogenic precursors (CD45-/PECAM1+/KDR+/VE-cadherin+) to study any effect of NA10 during the early stages of haematopoiesis. NA10 expression did not affect the frequency of CD34+/CD45+ primitive haematopoietic-committed cells, but an increase in Glycophorin-A+ cells, a marker for erythropoiesis, was noted. NA10 also enhanced the multilineage hematopoietic progenitor potential, due almost entirely to augmented erythropoietic progenitors. Further, GATA1, beta- and epsilon-haemoglobin were upregulated when compared to controls, and nuclei were detectable in differentiated erythroid cells from transduced hESC, indicative of primitive erythropoiesis. Overall this suggests a boost in the erythroid compartment following NA10 expression in hESC-derived hemogenic precursors. However studies at later-stages of haematopoiesis following NA10-transduction of CD34+/CD45+ progenitors isolated from hESC-derived EBs, demonstrated increased proliferation and a 32% increase in CFU-M (megakaryocyte colony-forming unit) formation alongside a 31% reduction in BFU-E (Burst forming unit erythroid) population) formation, suggesting a bias towards monocyte differentiation at the expense of erythropoiesis. These results show distinct stage-specific effects of NA10, dependent on the stage of haematopoietic development from hESC.

Studies such as this do not only give us further insight into the development of the hematopoietic system but may also be of therapeutic importance. The ability to boost the production of haematopoietic cells from hESCs, or indeed induced pluripotent stem cells, will no doubt enhance research efforts aimed at translating this basic science into something that could potentially save lives in the future.



The role of NUP98 gene fusions in hematologic malignancy.
Slape C, Aplan PD.
Leuk Lymphoma. 2004 Jul;45(7):1341-50.

HOXA10 is a critical regulator for hematopoietic stem cells and erythroid/megakaryocyte development.
Magnusson M, Brun AC, Miyake N, Larsson J, Ehinger M, Bjornsson JM, Wutz A, Sigvardsson M, Karlsson S.
Blood. 2007 May 1;109(9):3687-96.

Near-maximal expansions of hematopoietic stem cells in culture using NUP98-HOX fusions.
Ohta H, Sekulovic S, Bakovic S, Eaves CJ, Pineault N, Gasparetto M, Smith C, Sauvageau G, Humphries RK.
Exp Hematol. 2007 May;35(5):817-30.

Ectopic Expression of Nup98-HoxA10 Augments Erythroid Differentiation of Human Embryonic Stem Cells.
Ji J, Risueño RM, Hong S, Allan D, Rosten P, Humphries K, Bhatia M.
Stem Cells. 2011 Feb 15