I live in the Zebrafish, I am a hematopoietic stem cell (HSC) .


KK text image.img_assist_custom-320x274

My origin is a bit unknown as scientists hypothesise that I come from hemogenic endothelial cells. I first arise in the third week of human ontogeny inside yolk sac developing blood vessels, then, from the wall of the embryonic aorta and vitelline arteries one week later. From the yolk sac I transiently colonize the embryonic liver then permanently reside as niches in the bone marrow. I can undergo self-renewal, am highly quiescent and differentiate into all blood and immune cells which regulate blood hematopeosis. When I get older I would like to help protect the organism in which I reside from disease by eradicating defective cells therefore I think the path of Apoptosis is the way for me to follow.

Source : http://www.ncbi.nlm.nih.gov/pubmed/20711993



So how does the structure of this cell relate to its various functions?

HSC surface markers and the typical cytokines regulating HSCs are shown in the below picture:

SOURCE:  http://www.intechopen.com/books/innovations-in-stem-cell-transplantation/recent-advances-in-hematopoietic-stem-cell-gene-therapy

1. THROMBOPOIETIN(TPO)-  TPO and its receptor, c-Mpl, partake in early hematopoiesis from HSC . A deficiency in these factors show a decrease in progenitor cells of multiple hematopoitic lineages. TPO-mediated signal transduction for the self-renewal of HSCs is negatively regulated by the intracellular scaffold protein Lnk.

2. STEM CELL FACTOR (SCF)- involved in the proliferation and differentiation of hematopoietic progenitor cells.

3. ANGIOPOIETIN-1  – with its receptor Tie2 , regulates HSC dormancy by promoting the adhesion of HSCs to osteoblasts in the bone marrow niche and maintains long-term repopulating activity.

4. TRANSFORMING GROWTH FACTOR- TGF-β inhibits lipid raft clustering and induces p57Kip2 expression which in turn leads to HSC dormancy.