CFU-E stands for Colony Forming Unit-Erythroid. It arises from CFU-GEMM and gives rise to proerythroblasts.
Murine CFU-E assay
CFU-E is a stage of erythroid development between the BFU-E stage and the pro-erythroblast stage. CFU-E colony assay is designed to detect how many colony-forming-units of erythroid lineage there are in a hematopoietic tissue, which may be reflective of the organism’s demand for oxygen delivery to the tissues or a hematopoietic disorder. Early erythroid progenitors are found at a quite low frequency relative to later stages of erythroid differentiation, such as the pro-erythroblast and the basophilic erythroblast stages which can be detected by flowcytometry directly ex-vivo. Furthermore, unlike for the pro-erythroblast and later stages of erythroid development, no truly reliable and unique positive flow-cytometric markers exist, though it is possible to use negative exclusion markers to deplete a cell population of other precursors and differentiated cells by cell sorting, thus greatly enriching it for the CFU-E activity. CFU-E cells express Epo receptor, c-Kit, transferrin receptor, and are Ter119-negative. For the above reasons, the CFU-E assay, as inefficient and variable as it can often be, is still in use today. Cells at the CFU-E stage express some erythropoietin receptor, and thus can be induced to terminally differentiate in vitro in 2–3 days in the presence of only erythropoietin . Methylcellulose is a semisolid media additive that allows an investigator to stain and then count individual colonies, each arising from a single plated progenitor that is at the CFU-E stage. By day 2 from the time of plating, each CFU-E colony will contain between 8 and 64 hemoglobinized cells most of which are in their end-stage of erythroid differentiation. It is possible to see a small spectrum of hemoglobinization level and possibly cell size, indicating that some cells in the colony have achieved the end-stage faster than others. Cell number in a colony is important because pro-erythroblast stage is also Epo-responsive, but the proliferative capacity of these cells is not as high, thus yielding a colony with fewer than 8 cells. Likewise, an earlier stage of erythroid differentiation may also yield colonies in Epo-only medium, but these colonies would likely be smaller and/or not hemoglobinized, since the stages before the CFU-E stage require other factors and more time for growth that will also delay the terminal differentiation and hemoglobinization.
