Reelin, encoded by the RELN gene, is a large secreted extracellular matrix glycoprotein that helps regulate processes of neuronal migration and positioning in the developing brain by controlling cell–cell interactions. Besides this important role in early development, reelin continues to work in the adult brain. It modulates synaptic plasticity by enhancing the induction and maintenance of long-term potentiation. It also stimulates dendrite and dendritic spine development and regulates the continuing migration of neuroblasts generated in adult neurogenesis sites like the subventricular and subgranular zones. It is found not only in the brain but also in the liver, thyroid gland, adrenal gland, fallopian tube, breast and in comparatively lower levels across a range of anatomical regions.
As they travel through the rostral migratory stream, neuroblasts are held together, probably in part by thrombospondin-1's binding to the reelin receptors ApoER2 and VLDLR. As they arrive to the destination, the groups are dispersed by reelin and cells strike out on their individual paths. A fragment of an illustration from Lennington et al., 2003.
Reelin controls the direction of radial glia growth. A fragment of an illustration from Nomura T. et al., 2008. Reelin-expressing cells (red) on C stimulate the growth of green glial fibers, while on B, where the red cells do not express reelin, radial glia is more disarrayed.
Increased reelin expression changes the morphology of migrating neurons: unlike the round neurons with short branches (C) they assume bipolar shape (D) and attach themselves (E) to the radial glia fibers that are extending in the direction of reelin-expressing cells. Nomura T. et al., 2008.
Reelin stimulates the progenitor cells to differentiate into radial glia, inducing the expression of radial glial marker BLBP by affecting the NOTCH1 cascade. A fragment of an illustration from Keilani et al., 2008.
The very-low-density-lipoprotein receptor (VLDLR) is a transmembrane lipoprotein receptor of the low-density-lipoprotein (LDL) receptor family. VLDLR shows considerable homology with the members of this lineage. Discovered in 1992 by T. Yamamoto, VLDLR is widely distributed throughout the tissues of the body, including the heart, skeletal muscle, adipose tissue, and the brain, but is absent from the liver. This receptor has an important role in cholesterol uptake, metabolism of apolipoprotein E-containing triacylglycerol-rich lipoproteins, and neuronal migration in the developing brain. In humans, VLDLR is encoded by the VLDLR gene. Mutations of this gene may lead to a variety of symptoms and diseases, which include type I lissencephaly, cerebellar hypoplasia, and atherosclerosis.
VLDL receptor
The reelin pathway, representing VLDLR’s role in the process.
