C-Terminal Region Truncation of RELN Disrupts an Interaction with VLDLR, Causing Abnormal Development of the Cerebral Cortex and Hippocampus

• Published in: The Journal of neuroscience Vol. 37; no. 4; pp. 960 - 971
• Main Authors: Ha, Seungshin, Tripathi, Prem P, Mihalas, Anca B, Hevner, Robert F, Beier, David R
• Format: Journal Article
• Language: English
• Published: United States Society for Neuroscience 25.01.2017
• Subjects: Animals; Cell Adhesion Molecules, Neuronal - deficiency; Cell Adhesion Molecules, Neuronal - genetics; Cell Adhesion Molecules, Neuronal - metabolism; Cerebral Cortex - abnormalities; Cerebral Cortex - metabolism; Extracellular Matrix Proteins - deficiency; Extracellular Matrix Proteins - genetics; Extracellular Matrix Proteins - metabolism; Female; HEK293 Cells; Hippocampus - abnormalities; Hippocampus - metabolism; Humans; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Nerve Tissue Proteins - deficiency; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Protein Binding - physiology; Receptors, LDL - genetics; Receptors, LDL - metabolism; Serine Endopeptidases - deficiency; Serine Endopeptidases - genetics; Serine Endopeptidases - metabolism; APOER2; Reelin; VLDLR; mutagenesis
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.1826-16.2016

We discovered a hypomorphic reelin (Reln) mutant with abnormal cortical lamination and no cerebellar hypoplasia. This mutant, Reln , carries a chemically induced splice-site mutation that truncates the C-terminal region (CTR) domain of RELN protein and displays remarkably distinct phenotypes from reeler The mutant does not have an inverted cortex, but cortical neurons overmigrate and invade the marginal zone, which are characteristics similar to a phenotype seen in the cerebral cortex of Vldlr mice. The dentate gyrus shows a novel phenotype: the infrapyramidal blade is absent, while the suprapyramidal blade is present and laminated. Genetic epistasis analysis showed that Reln /Apoer2 double homozygotes have phenotypes akin to those of reeler mutants, while Reln /Vldlr mice do not. Given that the receptor double knock-out mice resemble reeler mutants, we infer that Reln /Apoer2 double homozygotes have both receptor pathways disrupted. This suggests that CTR-truncation disrupts an interaction with VLDLR (very low-density lipoprotein receptor), while the APOER2 signaling pathway remains active, which accounts for the hypomorphic phenotype in Reln mice. A RELN-binding assay confirms that CTR truncation significantly decreases RELN binding to VLDLR, but not to APOER2. Together, the in vitro and in vivo results demonstrate that the CTR domain confers receptor-binding specificity of RELN. Reelin signaling is important for brain development and is associated with human type II lissencephaly. Reln mutations in mice and humans are usually associated with cerebellar hypoplasia. A new Reln mutant with a truncation of the C-terminal region (CTR) domain shows that Reln mutation can cause abnormal phenotypes in the cortex and hippocampus without cerebellar hypoplasia. Genetic analysis suggested that CTR truncation disrupts an interaction with the RELN receptor VLDLR (very low-density lipoprotein receptor); this was confirmed by a RELN-binding assay. This result provides a mechanistic explanation for the hypomorphic phenotype of the CTR-deletion mutant, and further suggests that Reln mutations may cause more subtle forms of human brain malformation than classic lissencephalies.