A comprehensive diagram of human hematopoiesis
In histology, it is very difficult to distinguish it from the other "-blast" cells (lymphoblast, myeloblast, monoblast, and megakaryoblast). The cytoplasm is blue in an H&E stain, indicating that it is basophilic.
Proerythroblasts arise from the CFU-e (colony-forming unit erythroid) cells, and give rise to basophilic erythroblasts. In the mouse, proerythroblasts are large committed progenitors that express high levels of transferrin receptor (iron acquisition receptor), the erythropoietin receptor (EpoR), some c-Kit (stem cell factor receptor), and are Ter119 (cell surface molecule)-positive. Their proliferative capacity is more limited compared to the preceding stage, the CFU-e.
In vivo, starting with the proerythroblast stage, erythroid cells undergo several more cell divisions while at the same time upregulating survival genes such as Bcl-xL, acquiring and storing large amounts of iron, ramping up the synthesis of hemoglobin and other erythroid genes (in large part a GATA-1 dependent process that is augmented by the EpoR signaling) and decreasing in cell size, eventually removing their nuclei and being released into the bloodstream as a reticulocyte.
"Pronormoblast" vs. "proerythroblast"
Some sources consider the terms "pronormoblast" and "proerythroblast" to be synonyms. However, other sources consider "proerythroblast" to be a parent term, divided into the following two categories:
- "pronormoblast" - normal development
- "promegaloblast" - abnormal development
- Histology image: 01804loa - Histology Learning System at Boston University - "Bone Marrow and Hemopoiesis: bone marrow smear, erythroblast series with proerythroblast"
- Histology at OU 75_11
- Histology at KUMC blood-blood04
- Image and description at purdue.edu
- Histology of "promegaloblast" at marist.edu (pernicious anemia)
- Interactive image at usuarios.lycos.es
- Overview at temple.edu