Lymphangiogenesis – pt2 Flashcards
Q1: What is lymphangiogenesis and where does it begin?
A: Lymphangiogenesis is the formation of the lymphatic vasculature. It begins with progenitor cells in the cardinal vein, specified by transcription factors SOX18 and COUP-TFII, which express PROX1 and migrate dorsolaterally to form lymph sacs.
Q2: Why must lymphatic progenitors delay expressing full lymphatic markers while still in the vein wall?
A: Early expression of lymphatic markers would compromise vein integrity, which already carries blood. Thus, the program is temporarily halted and resumes after the cells migrate out.
Q3: How is directional migration of LECs achieved?
A: Through a VEGF-C gradient produced by non-endothelial mesenchymal cells, guiding migration to specific embryonic regions.
Q4: What ensures physical separation between lymphatic vessels and veins?
A: Platelets form clots at lymphovenous junctions. Key platelet gene SLP76 is critical—its loss results in blood leaking into lymphatics.
Q5: How does the lymphatic system mature postnatally?
A: It undergoes remodeling and valve formation, guided by VEGFR3 signaling. Valves ensure unidirectional flow of lymph fluid.
Q6: What transcription factor defines lymphatic endothelial cell identity?
A: PROX1
Q7: What receptor does VEGF-C signal through in LECs?
A: VEGFR3
Q8: What is the role of CCBE1 in lymphangiogenesis?
A: It is required for VEGF-C maturation, enabling effective VEGFR3 activation and LEC budding.
Q9: What does a “non-cell autonomous phenotype” mean?
A: A phenotype in one cell type caused by genetic defects in a different cell type (e.g., lymphatic defects due to platelet gene SLP76 loss).
Q10: What does the “K14” promoter target in transgenic models?
A: The skin, as K14 is expressed in keratinocytes.
Q11: What are lymph sacs and when do they form?
A: Early lymphatic clusters formed around 11.5 dpc, assembling from migrating PROX1+ progenitors.
Q12: If a gene is knocked out and lymphatics fail to develop, how can you prove it’s that gene causing the defect?
v\A: Perform a rescue experiment by reintroducing the gene or protein and restoring lymphatic development.
Q13: What would happen in a mouse overexpressing a soluble (non-functional) VEGFR3 receptor?
A: The soluble receptor would sequester VEGF-C, preventing signaling, leading to loss of lymphatic vessels (functional loss-of-function effect).
Q14: How did researchers show VEGF-C attracts lymphatic progenitors?
A: By placing VEGF-C-loaded beads into mutant embryos; progenitors migrated toward the bead, confirming chemoattraction.
Q15: In lineage tracing, why are some LECs red (Tomato+) and others green (GFP+)?
A: Green cells had Cre activation (from endothelial origin), red cells did not (possibly non-endothelial origin or incomplete recombination).
Q16: What model organism is ideal for forward genetics and why?
A: Zebrafish – high fecundity, transparent embryos, and visible vasculature make it excellent for mutagenesis screens.
Q17: What was the “full of fluid” zebrafish mutant and what gene was implicated?
A: A mutant with lymphatic edema; CCBE1 was identified as the mutated gene crucial for VEGF-C maturation and LEC migration.
Q18: What is the link between CCBE1 and VEGF-C?
A: CCBE1 enables proteolytic maturation of VEGF-C, allowing it to bind and activate VEGFR3.
Q19: Why is dorso-lateral polarization of LECs important?
A: It ensures progenitors only migrate away from the vein toward proper lymphatic regions, avoiding misrouting into blood vessels.
Q20: How do morpholinos work in zebrafish genetic screens?
A: They block mRNA translation, simulating gene knockdown to validate gene function (e.g., CCBE1 loss of function).
