hematopoiesis
The process of haematopoiesis occurs in several stages, and is controlled by at least 11 growth factors. The first stage involves the differentiation of a pluripotential stem cell into a committed progenitor, which is followed by maturation of committed progenitors in distinct pathways.
The common myeloid progenitor can generate:
● proerythroblasts (pronormoblasts) → erythropoiesis
● myeloblasts → granulopoiesis
● monoblasts → monocytopoiesis
● megakaryoblasts → thrombopoiesis
The common lympoid progenitor can generate:
● lymphoblasts → lymphopoiesis
Committed progenitor stage to mature cell : granulopoiesis
↓
myeloblast
↓
B/E/N promyelocyte
↓---↓---↓
B/E/N myelocyte
↓---↓---↓
B/E/N metamyelocyte
↓---↓---↓
B/E/N band
↓---↓---↓
basophil, eosinophil, neutrophil
↓ -----------------------
mast cell -----------------------
Committed progenitor stage to mature cell : lymphopoiesis
↓
lymphoblast
----------------------------------------↓ rearrangements H: D-J → H: V-DJ
prolymphocyte
-----------------↓ rearrangements L: V-J --------------------------↓
small lymphocyte------or----- natural killer cell (large granular lymphocyte)
------------↓ IgM→IgD ---------↓------------------------------------ ↓
------B lymphocyte--or-- T lymphocyte
------------↓----------------------------------------------------------- ↓
--------plasma cell------------------------------------------lymphoid dendritic cell
Development of mature B lymphocytes from multipotent progenitors requires the coordinated activities of a number of transcriptional regulatory proteins, including EBF, Pax-5, and E2A.
E2A proteins function in early B lineage development to regulate B lineage-specific gene expression as well as B cell survival. E2A-encoded proteins are involved in the differentiation of a number of cell types, and they are especially important in lymphocyte development.
The E2A gene encodes E47 and E12, which are basic-helix-loop-helix (bHLH) transcription factors that bind DNA either as homodimers or as heterodimers with other bHLH proteins. Such bHLH DNA binding activity in the B-lineage comprises E47 homodimers. Development of thymocytes mainly involves heterodimers of E47 and a related bHLH protein, HEB. Thymocytic E2A protein expression is required to initiate T-cell differentiation. During the development of thymoctyes, E-proteins and their antagonists, Id2 and Id3, regulate T-lineage specific gene expression and TCR rearrangement. E2A and Id proteins block thymocytic maturation in the absence of pre-TCR expression, and pre-TCR signaling acts to promote development in part by inhibiting E2A activity. [l]
Committed progenitor stage to mature cell : monocytopoiesis
↓
monoblast
↓
promonocyte
↓
↓ ----↓
macrophage or myeloid dendritic cell
Committed progenitor stage to mature cell : erythropoiesis
↓
proerythroblast
↓
basophilic erythroblast
↓
polychromatic erythroblast
↓
polychromatic erythrocyte (reticulocyte)
↓
erythrocyte (RBC)
Committed progenitor stage to mature cell : thrombopoiesis
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