Primary antibody solution was applied for 1?h at RT. DNA replication patterns and fail to complete maturation, causing lethal anemia. Our results indicate that hematopoietic progenitors are particularly sensitive to replication stress, and full origin licensing ensures their correct differentiation and functionality. The process of genomic duplication starts at replication origins, which are licensed in the G1 phase of the cell division cycle, several hours before their activation in S phase. The licensing Rabbit polyclonal to ADRA1B process is led by the origin recognition complex (ORC), cell division cycle 6 (CDC6) and Cdc10-dependent transcript 1 (CDT1) proteins, which cooperate to engage the mini-chromosome maintenance (MCM) complex with the DNA. MCM, composed by essential subunits MCM2-7, displays DNA helicase activity and becomes part of the replisome machinery (reviewed in references1,2). Defective control of DNA replication causes replicative stress’ (RS), which is the underlying cause of several developmental diseases. Mutations in ORC, CDC6 and CDT1 genes are related to Meier-Gorlin syndrome, a type of dwarfism3,4,5, and mutations in MCM4 are linked to growth retardation, adrenal insufficiency and natural killer cell deficiency6. Impaired MCM function also increases cancer susceptibility7,8,9,10,11,12,13 (reviewed in references14,15). MCM complexes are normally loaded onto DNA in excess relative to the number of origins that fire during the S phase (reviewed in reference16). One function of the surplus of MCM is to license dormant origins that may be activated in response to stalled or collapsed forks, providing a rescue mechanism under RS17,18,19. Another possible function for the high number of licensed origins, which remains largely underexplored, is to provide flexibility to the replication process during early embryonic development20,21 or in cell differentiation contexts that require the activation or shut-off of specific origins22,23,24 (reviewed in references25,26). To investigate the protective effects of MCM against RS and is well documented in the mouse, and MCM downregulation beyond 2/3 Ticagrelor (AZD6140) of its physiological levels causes embryonic lethality or promotes tumorigenesis in adults7,8,9,10,11,12,13. Therefore, it is likely that certain cell types in the developing embryo, such as stem and progenitor cells, are particularly sensitive to RS induced by low MCM levels. We have tested the hypothesis that different cell types may have different requirements for MCM concentration using a novel strain with hypomorphic Mcm3 expression. While Mcm3Lox/Lox MEFs proliferated and replicated DNA with approximately 1/3 of the normal concentration of MCM3 protein, a similar reduction severely impaired hematopoietic progenitors, indicating a stricter requirement for origin licensing in the latter. In mid-gestation, hematopoiesis in the fetal liver is largely geared towards the production of RBCs to guarantee oxygen delivery to the rapidly growing embryo. Interestingly, erythroid precursors undergo several rounds of DNA replication and cell division during terminal differentiation, and genetic models that ablate cell cycle regulators such as Rb, E2F4, E2F8 or D-cyclins frequently result in embryonic anemia35,36,37,38. While D-Cyclin/CDK and Rb/E2F constitute the axis of a large transcriptional pathway regulating multiple genes, here we report for the first time that downregulation of a single MCM gene is sufficient to impair hematopoietic progenitor cells, causing anemia. Cytological analyses of embryonic blood revealed lower counts of RBCs and abundance of immature nucleated erythroblasts. Furthermore, Ticagrelor (AZD6140) transplantation of Mcm3-deficient fetal liver cells into lethally irradiated mice reconstituted the adult RBC population with much lower efficiency than Mcm3-competent cells. Our results indicate that a full complement of MCM is required for erythrocyte maturation in steady-state conditions and in response to erythropoietic stress. If MCM levels drop to approximately 1/3 of its normal concentration, the severity of the anemia causes embryonic lethality in the C57BL/6 genetic background. As reported in other mouse models such as the Mcm4-chaos mutant8,11,12 or the Rif1 KO mouse39, Mcm3Lox/Lox embryonic lethality was partially alleviated in a mixed C57BL/6-CD1 background and it was further rescued by overexpression of CHK1 kinase, reinforcing the connection between RS and the phenotypes observed. To our knowledge, the single-molecule analyses of DNA replication in EB precursors isolated from the fetal liver provide the first evidence that the program Ticagrelor (AZD6140) of DNA replication undergoes active changes during the physiological maturation of mammalian erythrocytes. As pro-EBs proliferate and differentiate into mature reticulocytes, their.