F‑Spondin (floor plate and thrombospondin homology), also called Spondin‑1, SPON1 or VSGP (vascular smooth muscle growth‑promoting factor), is an approximately 110 kDa secreted glycoprotein that is a member of a subgroup of TSR (thrombospondin) molecules that are either membrane‑bound or associated with the extracellular matrix (ECM) (1‑3). Mouse F‑Spondin is synthesized as an 807 amino acid (aa) precursor with a 779 aa mature region that includes an N‑terminal reelin‑like domain, an F‑spondin (FS) domain, and six C‑terminal thrombospondin (TSP) type I repeats (1‑3). Mature mouse F‑Spondin shares 99% aa sequence identity with rat and 97% with human, bovine and canine F‑Spondin. TSP 5 and 6 bind ECM, while TSP 1‑4 plus the FS domain may mediate repulsive activity on motor neurons and outgrowth promoting activity on sensory neurons during development or after injury (2‑5). Crystal structure indicates that the reelin‑like domain binds heparin and may mediate weak dimerization (6). Plasmin cleavage generates a diffusible 95 kDa, 656 aa F‑spondin that lacks TSP 5 and 6, while non‑plasmin cleavage between the FS segment and the first TSP repeat generates 60 kDa and 50 kDa fragments (3, 4, 7). F‑Spondin shows unusual C‑mannosylation and O‑fucosylation within the TSP repeats (3). Mammalian cells expressing F‑spondin include floor plate epithelium, ventral motor neurons, Schwann cells, fibroblasts, hippocampal pyramidal cells, endothelial cells, vascular smooth muscle cells and some tumor cells (2‑5, 8). F‑Spondin can either tether cells to the ECM or interfere with integrin adhesion, thus either blocking or allowing nerve or vascular endothelial cell migration (3, 9). It binds beta ‑amyloid fibrils and inhibits beta ‑secretase cleavage, thus reducing A beta  plaque deposition associated with Alzheimer’s disease (10, 11). F‑Spondin is also reported to inhibit differentiation or migration during angiogenesis (affecting endothelial cells) and bone development (affecting osteoclast and chondrocyte precursors) (3, 9, 12, 13).