Role of VEGF-C/VEGFR3 system in lymphatic patterning during lymph node development

Abstract

The development of lymphatic vessels (LVs) and lymph nodes (LNs) occurs in a coordinated fashion during embryogenesis. Although the LN ontogeny is well known, its current morphology has been established mainly based on section immunohistological approaches limiting further spatiotemporal pattern analysis in three dimensions which needs to be elucidated. Here, I demonstrate additional structural perspectives of LVs during LN anlagen development by analyzing Prox1-GFP and $Vegfc^{+/LacZ}$ mouse models through whole mount immunohistochemical protocol. Prox1+ lymphatic endothelial cells (LECs) formed string-like connections rather than the lymph sac-like structures until E14.5 and the LEC coverage around the anlagen was complete before birth. $Vegfc^{+/LacZ}$ mice exhibited markedly smaller LNs in neonates and adults, presumably due to a decrease in LTi cell clusters and migrating $Prox1^+$ LECs during embryogenesis, indicating that the VEGF-C/VEGFR3 signaling plays an important role in normal LN formation through proper migration and organization of the LECs in the embryos. In addition, Vegfc- haploinsufficiency or inhibition of VEGFR3 signaling resulted in an impairment in LN LV ingrowth at postnatal day 3, leading to a significant decrease in LN volumes. During acute inflammation, $Vegfc^{+/LacZ}$ mice exhibited decreased LN LV expansion as well as smaller LNs. Taken together, my findings provide useful anatomical information to current model of mouse LN formation in relation to the LVs, and compelling evidences supporting that LV contribution through VEGF-C/VEGFR3 signaling is critical in LN development and maturation.