A proerythroblast is the earliest of four stages in development

Cellular differentiation

In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a simple zygote to a complex system of...

 of the normoblast

Normoblast

An erythroblast is a type of red blood cell which still retains a cell nucleus. It is the immediate precursor of a normal erythrocyte.-Nomenclature:...

.

In histology

Histology

Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...

, it is very difficult to distinguish it from the other "-blast" cells (lymphoblast

Lymphoblast

Lymphoblasts are immature cells which typically differentiate to form mature lymphocytes. Normally lymphoblasts are found in the bone marrow, but in acute lymphoblastic leukemia , lymphoblasts proliferate uncontrollably and are found in large numbers in the peripheral blood.The size is between 10...

, myeloblast

Myeloblast

The myeloblast is a unipotent stem cell, which will differentiate into one of the actors of the Granulocyte series.- Origin :These cells descend from the primitive reticulum cells, which are found in the stroma of the marrow. There is also an intermediate phase between the myeloblast and these...

, monoblast

Monoblast

Monoblasts are normally found in bone marrow and do not appear in the normal peripheral blood. They mature into monocytes which, in turn, develop into macrophages.-Structure:...

, and megakaryoblast

Megakaryoblast

A megakaryoblast is a precursor cell to a promegakaryocyte, which in turn becomes a megakaryocyte during haematopoiesis. It is the beginning of the thrombocytic series....

). The cytoplasm

Cytoplasm

The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...

 is blue in an H&E stain

H&E stain

H&E stain, HE stain or hematoxylin and eosin stain is a popular staining method in histology. It is the most widely used stain in medical diagnosis; for example when a pathologist looks at a biopsy of a suspected cancer, the histological section is likely to be stained with H&E and termed H&E...

, indicating that it is basophilic

Basophilic

Basophilic is a technical term used by histologists. It describes the microscopic appearance of cells and tissues, as seen down the microscope, after a histological section has been stained with a basic dye. The most common such dye is haematoxylin....

.

Proerythroblasts arise from the CFU-e

CFU-E

CFU-E is a colony forming unit.It arises from CFU-GEMMUnderstanding the murine CFU-e assay :CFU-e is a stage of erythroid development between the BFU-e stage and the pro-erythroblast stage...

 (colony-forming unit erythroid

Red blood cell

Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...

) cells, and give rise to basophilic erythroblasts. In the mouse

Mouse

A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...

, proerythroblasts are large committed progenitors

Progenitor cell

A progenitor cell is a biological cell that, like a stem cell, has a tendency to differentiate into a specific type of cell, but is already more specific than a stem cell and is pushed to differentiate into its "target" cell...

 that express high levels of transferrin receptor

Transferrin receptor

Transferrin receptor is a carrier protein for transferrin. It is needed for the import of iron into the cell and is regulated in response to intracellular iron concentration...

 (iron acquisition receptor), the erythropoietin receptor

Erythropoietin receptor

The erythropoietin receptor is a protein that in humans is encoded by the EPOR gene. EpoR is a 59 kDa peptide and is a member of the cytokine receptor family. EpoR pre-exists as dimers...

 (EpoR), some c-Kit (stem cell factor receptor), and are Ter119 (cell surface molecule

Cell adhesion molecule

Cell Adhesion Molecules are proteins located on the cell surface involved with the binding with other cells or with the extracellular matrix in the process called cell adhesion....

)-positive. Their proliferative capacity is more limited compared to the preceding stage, the CFU-e.

In vivo

In vivo

In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...

, starting with the proerythroblast stage, erythroid cells undergo several more cell divisions while at the same time upregulating survival genes such as Bcl-xL

Bcl-xL

B-cell lymphoma-extra large is a transmembrane molecule in the mitochondria. It is involved in the signal transduction pathway of the FAS-L. It is one of several anti-apoptotic proteins which are members of the Bcl-2 family of proteins. It has been implicated in the survival of cancer cells. Other...

, acquiring and storing large amounts of iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, ramping up the synthesis of hemoglobin

Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

 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

Cell nucleus

In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...

 and being released into the bloodstream as a reticulocyte

Reticulocyte

Reticulocytes are immature red blood cells, typically composing about 1% of the red cells in the human body.Reticulocytes develop and mature in the red bone marrow and then circulate for about a day in the blood stream before developing into mature red blood cells. Like mature red blood cells,...

.

"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

External links

- "Bone Marrow and Hemopoiesis: bone marrow smear, erythroblast series with proerythroblast"

• Image and description at purdue.edu
• Histology of "promegaloblast" at marist.edu (pernicious anemia
  Pernicious anemia
  Pernicious anemia is one of many types of the larger family of megaloblastic anemias...
  
  )
• Interactive image at usuarios.lycos.es
• Overview at temple.edu