Loss of meningeal lymphatic endothelial cells results in formation of a newly forming vascular network with scavenging function.

For an extended period of time, the meninges were believed to be devoid of lymphatic vessels. The recent discovery of lymphatic vessels in the dura mater of humans, mice and zebrafish, and the identification and characterization of scavenging lymphatic endothelial cells in zebrafish leptomeninges have contributed to a better understanding of waste removal routes from the brain. Zebrafish brain lymphatic endothelial cells (BLECs), in particular, have a high propensity for particulate waste removal from the cerebrospinal fluid. To further understand the function of BLECs, we have established a protocol for specifically ablating this cell type during embryonic stages. We show that BLECs do not recover upon complete depletion, even at adult stages. The absence of BLECs results in detrimental effects on the meningeal blood vasculature and on arachnoid mater structure. We further report that, upon BLEC ablation, a vessel network forms, which shares characteristics with lymphatic vessels and is able to take up substances injected into the brain parenchyma, thus possibly providing compensatory functions in the absence of BLECs.