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Hematopoiesis
MYB bi-allelic targeting abrogates primitive clonogenic progenitors while the emergence of primitive blood cells is not affected
Ferrata Storti Foundation
Haematologica 2021 Volume 106(8):2191-2202
Zahir Shah,1,2,3 Elena S. Philonenko,1,2,4 Vasily Ramensky,5,6 Chenyu Fan,1,2,3 Cuihua Wang,1,2 Hanif Ullah,1,2,3 Baoyun Zhang,1,2 Pavel Volchkov5
and Igor M. Samokhvalov1,2
1Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Science, Guangzhou, China; 2Key Laboratory of Regenerative Biology, Chinese Academy of Science, Guangdong Provincial Key Laboratory of Stem Cells and Regenerative Medicine, Guangzhou, China; 3University of Chinese Academy of Science, Beijing, China; 4Vavilov Institute of General Genetics, Russian Academy of Science, Moscow, Russia; 5Moscow Institute of Physics and Technology, Dolgoprudny, Moscow, Russia and 6National Medical Research Center for Preventive Medicine, the Ministry of Healthcare of the Russian Federation, Moscow, Russia
ABSTRACT
MYB is a key regulator of definitive hematopoiesis and it is dis- pensable for the development of primitive hematopoietic cells in vertebrates. In order to delineate definitive versus primitive hematopoiesis during differentiation of human embryonic stem cells, we have introduced reporters into the MYB locus and inactivated the gene by bi-allelic targeting. In order to recapitulate the early developmental events more adequately, mutant and wild-type human embryonic stem cell lines were differentiated in defined culture conditions without the addition of hematopoietic cytokines. The differentiation of the reporter cell lines demonstrated that MYB is specifically expressed throughout emerging hematopoietic cell populations. Here we show that the disrup- tion of the MYB gene leads to severe defects in the development and pro- liferation of primitive hematopoietic progenitors while the emergence of primitive blood cells is not affected. We also provide evidence that MYB is essential for neutrophil and T-cell development and the upregulation of innate immunity genes during hematopoietic differentiation. Our results suggest that the endothelial origin of primitive blood cells is direct and does not include the intermediate step of primitive hematopoietic progenitors.
Introduction
Mammalian hematopoietic development is a multistage process that occurs in two distinct sites of the vertebrate conceptus, the yolk sac and the embryo proper. The primitive hematopoietic program of the yolk sac is transient and restricted to a few blood cell lineages. The earliest clonogenic hematopoietic progenitors arise within the extraembryonic mesoderm of the mid-streak mouse conceptus and pre- cede the appearance of first hemoglobinized erythroblasts by about 1.5 days of gestation.1,2 The primitive hematopoietic progenitors are thought to give rise to all primitive erythroblasts and other primitive blood cells.1,3,4 The progenitor-derived primitive erythroblasts gradually mature and ultimately enucleate within mouse embryo circulation.5
Myb, one of the key hematopoietic transcription factors, is essential for the maintenance of definitive hematopoietic progenitors with high proliferative poten- tial.6 In the developmental context, the Myb gene is expressed in the definitive ery- throid precursors of mouse fetal liver but is not detected in primitive erythroid cells of the yolk sac.7 The homozygous disruption of Myb is embryonic lethal by E15.5 due to progressive anemia caused by defects in the definitive erythropoiesis, whereas primitive hematopoiesis is not affected.8 The role of MYB in human hematopoiesis has been studied using the hematopoietic differentiation of human pluripotent stem cells (hPSC) in vitro as a model of human hematopoietic develop-
Correspondence:
IGOR M. SAMOKHVALOV
igor@gibh.ac.cn
Received: February 4, 2020. Accepted: July 28, 2020. Pre-published: July 30, 2020.
https://doi.org/10.3324/haematol.2020.249193
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