Endothelial Cells Filopodia in the Anastomosis of Central Nervous System Capillaries

In this article we explore filopodia of endothelial cells (ECs) in the developing central nervous system (CNS) using the Golgi method and transmission electron microscopy. Filopodia of ECs play a crucial role in the anastomosis of growing capillaries of the CNS. The leading ECs filopodia from approaching capillaries interconnect forming complex conglomerates that precede the anastomotic event. The contacting filopodia form narrow spaces between them filled with proteinaceous basal lamina material. The original narrow spaces coalesce into larger ones leading to the formation of a single one that will interconnect (anastomose) the two approaching capillaries. The four leading ECs (two for each approaching capillary) become the wall of the newly formed post-anastomotic CNS capillaries. These new CNS capillaries are very small with narrow and irregular lumina that might permit the passage of fluid but not yet of blood cells. Eventually, their lumen enlarges and permits the passage of blood cells.