Characterizing Intracranial Lymphatic Development in Zebrafish

The recent discovery of meningeal lymphatics in mammals is reshaping our understanding of fluid homeostasis and cellular waste management in the brain. The optical clarity and experimental advantages of zebrafish have made this an essential model organism for studying lymphatic development, but the existence of meningeal lymphatics has not yet been reported in this species. Using high-resolution optical imaging of the meninges in living adult transgenic animals, we show that zebrafish possess a meningeal lymphatic network comparable to that found in mammals. Using vital staining of the skull we are able to distinguish between extracranial lymphatics and intracranial lymphatics in living zebrafish. We confirm that the meningeal lymphatic network is separate from the blood vascular network by injecting fluorescent quantum dots into the blood vasculature and demonstrating that they fail to enter the lymphatic network. We also show that meningeal lymphatic vessels drain interstitial fluid from the brain by injecting fluorescent quantum dots into the brain and observing their drainage through the lymphatic vessels. This exciting new discovery opens up new avenues for experimental analysis of meningeal lymphatic development and meningeal lymphatic function as it relates to environmental and genetic insult, aging, and disease.