Transcription factor FOXP2 is a flow‐induced regulator of collecting lymphatic vessels
Magda Nohemí Hernández-Vásquez, Maria H. Ulvmar, Alejandra González‐Loyola, Ioannis Kritikos, Ying Sun, Liqun He, Cornelia Halin, Tatiana V. Petrova, Taija Mäkinen
Abstract
The lymphatic system is composed of a hierarchical network of fluid absorbing lymphatic capillaries and transporting collecting vessels. Despite distinct functions and morphologies, molecular mechanisms that regulate the identity of the different vessel types are poorly understood. Through transcriptional analysis of murine dermal lymphatic endothelial cells (LECs), we identified Foxp2, a member of the FOXP family of transcription factors implicated in speech development, as a collecting vessel signature gene. FOXP2 expression was induced after initiation of lymph flow in vivo and upon shear stress on primary LECs in vitro. Loss of FOXC2, the major flow‐responsive transcriptional regulator of lymphatic valve formation, abolished FOXP2 induction in vitro and in vivo. Genetic deletion of Foxp2 in mice using the endothelial‐specific Tie2‐Cre or the tamoxifen‐inducible LEC‐specific Prox1‐CreERT2 line resulted in enlarged collecting vessels and defective valves characterized by loss of NFATc1 activity. Our results identify FOXP2 as a new flow‐induced transcriptional regulator of collecting lymphatic vessel morphogenesis and highlight the existence of unique transcription factor codes in the establishment of vessel‐type‐specific endothelial cell identities. Molecular mechanisms that regulate the identity of functionally specialized lymphatic vessel types are incompletely understood. The current study identifies transcription factor FOXP2 as a signature gene and a critical transcriptional regulator of collecting lymphatic vessels. Speech‐linked FOXP2 is a specific marker of collecting lymphatic vessels that regulates lymphatic vessel and valve morphogenesis downstream of flow‐responsive transcriptional regulator FOXC2.