#hematopoietic stem cells

Stem Cell -l

Hematopoietic stem cells (HSCs) can differentiate into:

Hematopoietic stem cells reside in bone marrow endosteal and perivascular niches, characterized by CD34, Sca-1, c-Kit markers in mouse. They are multipotent, giving rise to all blood lineages through stepwise commitment: common myeloid progenitor producing erythrocytes, platelets, granulocytes, monocytes, and common lymphoid progenitor producing B, T, and NK cells. Regulation involves transcription factors GATA1, PU.1, Ikaros, cytokines SCF, IL-3, IL-7. HSCs do not generate neurons, epithelial cells, or muscle fibers under normal physiology, maintaining strict hematopoietic fate through niche-derived Notch and Wnt signals.

Ref: Orkin & Zon, Cell 2008; Gilbert, 12th ed., Chapter 6: Hematopoietic stem cells.

View Details

Stem Cell -l

The ability of hematopoietic stem cells to differentiate into blood cells makes them:

Hematopoietic stem cells residing in specialized bone marrow niches generate diverse mature blood lineages including erythroid, megakaryocytic, myeloid and lymphoid branches but do not produce neural, skeletal muscle, or extraembryonic trophoblast under physiological conditions in vivo. This pattern of generating multiple differentiated types related within one physiological system but limited outside defines multipotency precisely. Multipotent stem cells are lineage-restricted compared with pluripotent embryonic stem cells, yet maintain extensive self-renewal and produce several distinct terminal types through successive oligopotent progenitor intermediates regulated by master transcription factors GATA, PU.1, and Ikaros governing commitment.

Ref: Orkin & Zon, Cell 2008; Seita & Weissman 2010: Hematopoietic multipotency restricted to blood lineages.

View Details

Stem Cell -ll

What is the correct order of lineage commitment in hematopoietic differentiation?

Early embryonic hierarchy commences from totipotent zygote capable of forming whole organism including extraembryonic placenta and yolk sac membranes required for implantation. First lineage decision segregates trophectoderm outer epithelium, leaving inner cell mass as pluripotent source of epiblast which later forms three germ layers ectoderm, mesoderm, endoderm through gastrulation. Progressively, definitive hematopoietic stem cells arising in aorta-gonad-mesonephros region become multipotent blood-restricted, while subsequent progenitors such as common myeloid progenitor and later megakaryocyte-erythroid progenitors become increasingly unipotent. This sequential restriction mirrors epigenetic silencing of potency genes.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Totipotent to Unipotent lineage commitment stepwise restriction.

View Details

Stem Cell -ll

Which stem cell type is responsible for hematopoiesis?

Hematopoiesis throughout adult life depends on rare hematopoietic stem cells located in bone marrow endosteal and perivascular niches near sinusoids. These CD34 positive, lineage negative, Sca1 positive cells self-renew and generate common myeloid and common lymphoid progenitors that sequentially produce erythrocytes, platelets, neutrophils, monocytes, B and T lymphocytes. Transplantation of single HSC can reconstitute entire blood system of lethally irradiated recipients, demonstrating multipotency. Totipotent cells form extraembryonic tissues, neural stem cells generate glia and neurons, mesenchymal cells generate bone and stroma, not hematopoietic lineages robustly.

Ref: Weissman, Science 2000; Orkin & Zon, Cell 2008: Hematopoietic stem cells multipotent blood formation.

View Details

Stem Cell -lll

Hematopoietic stem cells (HSCs) are classified as:

Hematopoietic stem cells isolated from bone marrow as lineage negative Sca1 positive cKit positive population sustain all blood lineages including myeloid granulocytes, monocytes, erythroid cells and lymphoid B and T cells but not extraembryonic or non-hematopoietic tissues, defining multipotency within hematopoietic system. They self-renew long-term repopulating irradiated recipients and serial transplantation, generate committed progenitors common myeloid progenitor and common lymphoid progenitor via transcription factors GATA1, PU.1, Ikaros. Totipotent generates entire organism including placenta, pluripotent all embryonic lineages, unipotent single lineage like spermatogonial stem. Multipotent classification reflects restricted potential to multiple lineages within one germ layer derived system maintaining lifelong hematopoiesis.

Ref: Orkin and Zon, Hematopoiesis, Chapter 2: Multipotent Hematopoietic Stem Cells Classification.

View Details