Extracellular matrix serine protease that plays a role in layering of neurons in the cerebral cortex and cerebellum. Regulates microtubule function in neurons and neuronal migration. Affects migration of sympathetic preganglionic neurons in the spinal cord, where it seems to act as a barrier to neuronal migration. Enzymatic activity is important for the modulation of cell adhesion. Binding to the extracellular domains of lipoprotein receptors VLDLR and LRP8/APOER2 induces tyrosine phosphorylation of DAB1 and modulation of TAU phosphorylation. Oligomer of disulfide-linked homodimers. Binds to the ectodomains of VLDLR and LRP8/APOER2. The major isoform 1 is neuron-specific. It is abundantly produced during brain ontogenesis by the Cajal-Retzius cells and other pioneer neurons located in the telencephalic marginal zone and by granule cells of the external granular layer of the cerebellum. Expression is located in deeper layers in the developing hippocampus and olfactory bulb, low levels of expression are also detected in the immature striatum. At early developmental stages, expressed also in hypothalamic differentiation fields, tectum and spinal cord. A moderate to low level of expression occurs in the septal area, striatal fields, habenular nuclei, some thalamic nuclei, particularly the lateral geniculate, the retina and some nuclei of the reticular formation in the central field of the medulla. Very low levels found in liver and kidney. No expression in radial glial cells, cortical plate, Purkinje cells and inferior olivary neurons. The minor isoform 2 is only expressed in non neuronal cells. The minor isoform 3 is found in the same cells as isoform 1, but is almost undetectable in retina and brain stem. First detected at embryonic day 11.5. Expression increases up to birth and remains high from postnatal day 2 to 11 in both cerebellum and fore/midbrain. Expression declines thereafter and is largely brain specific in the adult. The basic C-terminal region is essential for secretion. N-glycosylated and to a lesser extent also O-glycosylated. Defects in Reln are the cause of the autosomal recessive reeler (rl) phenotype which is characterized by impaired motor coordination, tremors and ataxia. Neurons in affected mice fail to reach their correct locations in the developing brain, disrupting the organization of the cerebellar and cerebral cortices and other laminated regions. Belongs to the reelin family.