3 - hematopoiesis & angiogenesis

Cre Lox system enzyme

Cre recombinase (cuts DNA btwn lox sites)

LoxP sites

34 bp sequences from bacteriophages that allow recombination btwn sites

CreLox system purposes

genetic manipulations like deletions, insertions, translocations, inversions, activations, repressions, etc.

components needed for tissue specific cre lox

• tissue specific promoter (to drive Cre expression)

• gene flanked by loxP sites (floxed)

mesoderm differentiates into…

bone (BMP), hemangioblast, muscle (Fgf2)

angioblasts differentiate into…

endothelial cells (in vessels) via VEGF

initial site of vasculogenesis & hematopoiesis

outside the mammalian embryo in the yolk sac

vasculogenesis

de novo creation of blood vessels

angiogenesis

remodeling and pruning of primary network into distinct artery, vein, and capillary beds

vasculogenesis —> angiogenesis steps

1. mesoderm cells —> hemangioblasts

2. hemangioblasts form blood islands

3. tube formation with endothelial cell interactions

4. pericytes support vessel integrity

5. pruning and remodeling

Vascular endothelial growth factors (VEGFs)

initiate vessel formation (vasculogenesis)

secreted ligands —> activate VEGFRs

vegf-a mutant

thin vessels or just dorsal aorta but no sprouts

vegf-c mutant

edemic (build up of fluid under skin) & no lymphatic vasculature

vegfa +/- or vegfr2 -/-

no blood islands —> no vasculogenesis (die)

vegfb -/-

normal, small hearts

vegfr1 -/-

excess endothelial cells disorganized vessels

pigf -/- (placental growth factor)

normal embryonic vessels

vegf-a overexpression

hypervascularization

pathological angiogenesis

blood vessel growth when you don’t want it

ex. cancer, macular degeneration, tumor invasion

hematopoietic stem cell (HSC)

self renewing cells that, upon division, give rise to a new HSC and progenitor cell

• can repopulate the entire blood system

primitive to definitive hematopoiesis

yolk sac —> agm (aorta gonad) —> fetal liver —> bone marrow

primitive hematopoiesis

• occurs in yolk sac

• transient

• gives rise to mostly RBCs

definitive hematopoiesis

give rise to the first true HSCs

• first HSCs born in aorta gonad mesonephros (AGM)

• develop in the ventral wall of dorsal aorta

runx1 TF knockout

no development of HSCs in AGM so no fetal liver hematopoiesis