This is a mechanism module, not a disease entry and not a generic "lissencephaly" bucket. Disorder entries should conform to this module only when the core pathograph is Reelin pathway control of terminal somal translocation and cortical lamination. Primary RELN and VLDLR disease entries can map to the core ligand/receptor skeleton. Disease-specific entries with PI3K-AKT-mTOR activation should use this module only for a secondary AKT3-FOXG1-Reelin misexpression branch, and should otherwise conform to an overgrowth/mTOR module if that is the dominant skeleton. Do not use this as the primary skeleton for microtubule-dependent neuronal migration arrest, neural progenitor centrosome-spindle failure, apical neuroependyma integrity failure, pial basement-membrane/radial-glial endfoot failure, or interneuronopathy.
Reelin Terminal Translocation and Lamination Model
reelin_terminal_translocation_model
CANONICAL
Evidence: 3
Evidence balance
3 support
Reelin secreted by Cajal-Retzius cells in the marginal zone binds VLDLR and ApoER2/LRP8 on migrating neurons, activating DAB1 and downstream adhesion and cytoskeletal effectors. Failure of this signal impairs glia-independent somal translocation and leading-process stabilization, so late and early cortical neurons fail to settle in the proper inside-out order. The same pathway also organizes hippocampal and cerebellar development, explaining the recurring association of cortical lamination defects with hippocampal and cerebellar hypoplasia or disorganization.
Which parts of the RELN/VLDLR/LRP8/DAB1 terminal-translocation mechanism are adequately captured by mouse reeler and pathway-mutant models, and which require human iPSC-derived cortical organoids or organotypic human cortical assays to resolve human-specific progenitor, lamination, seizure, hippocampal, or cerebellar branches?
HUMAN MODEL MISMATCH
OPEN
gap_reelin_human_model_translatability
Attached to:
Cajal-Retzius Reelin Ligand Deficiency
VLDLR-ApoER2-DAB1 Signal Transduction Failure
Terminal Somal Translocation Failure
AKT3-FOXG1 Secondary Reelin Misexpression Branch
The seed review treats Reelin as one of the better conserved mouse-human MCD mechanisms, but it also emphasizes model-system limitations across cortical malformation curation. This should be represented as a human/model mismatch knowledge gap: mouse reeler, Vldlr/Apoer2, Dab1, ephrin-B, and Clasp2 models can establish the core terminal-translocation mechanism, but human iPSC-derived cortical organoids or organotypic human-tissue assays may be needed to test outer-radial-glia context, human-specific timing, seizure-relevant circuitry, and whether AKT3-FOXG1-driven Reelin misexpression follows the same branch.
Proposed experiments:
Isogenic Reelin-pathway cortical-organoid terminal-translocation panel
Cajal-Retzius Reelin Ligand Deficiency
trigger
Pathogenic RELN variants reduce or alter the secreted Reelin cue normally produced by Cajal-Retzius cells in the developing cortical marginal zone. Loss of this ligand deprives postmitotic neurons of the extracellular positioning signal required for terminal translocation and inside-out lamination.
Downstream
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VLDLR-ApoER2-DAB1 Signal Transduction Failure
Show evidence (2 references)
"An autosomal recessive form of lissencephaly (LCH) associated with severe abnormalities of the cerebellum, hippocampus and brainstem maps to chromosome 7q22, and is associated with two independent mutations in the human gene encoding reelin (RELN)."
Human genetics links RELN mutation to the cortical, hippocampal, cerebellar, and brainstem malformation pattern represented by this module.
"The mutations disrupt splicing of RELN cDNA, resulting in low or undetectable amounts of reelin protein."
Supports ligand deficiency as a proximal trigger in human RELN-associated lissencephaly with cerebellar hypoplasia.
VLDLR-ApoER2-DAB1 Signal Transduction Failure
central effector
Reelin normally binds VLDLR and ApoER2/LRP8 on migrating neurons, causing DAB1 activation through Src-family kinase signaling. Pathogenic VLDLR loss, RELN receptor-binding defects, or impaired DAB1 pathway propagation reduce the signal that couples the extracellular Reelin cue to neuron-intrinsic migration and lamination effectors.
Downstream
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Rap1-Cadherin Leading Process Instability
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Ephrin-B and CLASP2 Reelin Effector Branch
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Hippocampal and Cerebellar Organization Defect
Show evidence (3 references)
"A 199-kb homozygous deletion encompassing the entire very low density lipoprotein receptor (VLDLR) gene was present in all affected individuals."
Human VLDLR deletion supports receptor loss as an upstream Reelin-pathway lesion.
"VLDLR is part of the reelin signaling pathway, which guides neuroblast migration in the cerebral cortex and cerebellum."
Links VLDLR to Reelin-guided migration in cortex and cerebellum.
"A RELN-binding assay confirms that CTR truncation significantly decreases RELN binding to VLDLR, but not to APOER2."
Supports a receptor-binding-specific hypomorphic branch in which altered RELN preferentially disrupts VLDLR interaction.
Rap1-Cadherin Leading Process Instability
effector
Impaired DAB1 signaling reduces Rap1-dependent regulation of cadherin adhesion, destabilizing the leading processes of translocating cortical neurons. This node captures the neuron-intrinsic effector step that links the Reelin receptor-adaptor signal to terminal somal translocation.
Downstream
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Terminal Somal Translocation Failure
Show evidence (2 references)
"During migration, Dab1 acts in translocating neurons to stabilize their leading processes in a Rap1-dependent manner."
Places Dab1 upstream of Rap1-dependent leading-process stabilization in translocating cortical neurons.
"Rap1, in turn, controls cadherin function to regulate somal translocation."
Links Rap1 to cadherin-dependent control of somal translocation.
Ephrin-B and CLASP2 Reelin Effector Branch
amplifier
Ephrin-B proteins and CLASP2 represent Reelin-associated effector or modulator branches that influence DAB1 phosphorylation, cytoskeletal dynamics, neurite extension, motility, and neuronal positioning. This is a branch off the core pathway rather than a separate disease skeleton unless a disorder-specific entry demonstrates primary disruption of this branch.
Downstream
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Terminal Somal Translocation Failure
Show evidence (3 references)
"Here we show that the neuronal guidance cues ephrin B proteins are essential for Reelin signalling during the development of laminated structures in the brain."
Supports ephrin-B proteins as Reelin-pathway components affecting laminated brain structures.
"Importantly, activation of ephrin Bs can rescue the reeler neuronal migration defects in the absence of Reelin protein."
Supports ephrin-B signaling as a functional modifier branch capable of rescuing Reelin-loss migration defects in model systems.
"Together, our data reveal that CLASP2 is an essential Reelin effector orchestrating cytoskeleton dynamics during brain development."
Supports CLASP2 as a cytoskeletal effector downstream of Reelin signaling.
Terminal Somal Translocation Failure
central effector
Developing cortical neurons fail to complete the glia-independent terminal somal translocation step, often retracting or destabilizing leading processes after contact with the marginal zone. This failure is the central cellular mechanism distinguishing this module from earlier locomotion or microtubule-based migration arrest modules.
Downstream
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Cortical Lamination and Gyral Simplification
Show evidence (2 references)
"Dab1, an essential component of the reelin pathway, is required in radially migrating neurons for glia-independent somal translocation, but not for glia-guided locomotion."
Directly separates Reelin/Dab1 terminal somal translocation from glia-guided locomotion.
"Furthermore, cell-autonomous neuronal deficits in somal translocation are sufficient to cause severe neocortical lamination defects."
Shows that the translocation defect is sufficient to drive the lamination endpoint.
Cortical Lamination and Gyral Simplification
consequence
Failed terminal translocation and Reelin-pathway signaling produce disrupted inside-out lamination, simplified gyral patterning, pachygyria or lissencephaly-like cortical malformation depending on disease context and severity. Disease entries should instantiate the specific imaging or histopathologic endpoint rather than treating this module endpoint as a single disease.
Show evidence (2 references)
"Patient 1 had profound motor and intellectual disability with moderate lissencephaly suggestive of RELN mutations and was shown to harbor a splicing homozygous RELN mutation."
Human RELN-associated disease includes a lissencephaly cortical endpoint.
"These patients showed mild simplification or thickening of cortical gyration and had VLDLR mutations."
Human VLDLR-associated disease includes simplified or thickened cortical gyration, supporting a milder receptor-branch endpoint.
Hippocampal and Cerebellar Organization Defect
consequence
Reelin-pathway disruption affects laminated structures beyond neocortex, especially hippocampal formation and cerebellum. Human RELN/VLDLR disease and mouse Reln/Vldlr/ApoER2 pathway models show recurring hippocampal and cerebellar abnormalities, while RELN receptor-binding hypomorphs can uncouple cortical/hippocampal defects from cerebellar hypoplasia.
Show evidence (3 references)
"LCH parallels the reeler mouse mutant (Reln(rl)), in which Reln mutations cause cerebellar hypoplasia, abnormal cerebral cortical neuronal migration and abnormal axonal connectivity."
Links human RELN disease with the reeler mouse phenotype and cerebellar hypoplasia/cortical migration abnormalities.
"All patients had profound cerebellar hypoplasia on MRI with peculiar cerebellar morphology, associated with flattened pons and neocortical abnormalities."
Human cohort evidence supports cerebellar and neocortical involvement in RELN/VLDLR pathway disorders.
"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."
Supports subtype-specific branching: some RELN hypomorphs affect cortex and hippocampus without the full cerebellar hypoplasia branch.
AKT3-FOXG1 Secondary Reelin Misexpression Branch
amplifier
In focal cortical malformations driven by mosaic AKT3 activation, Reelin can be misexpressed through FOXG1-dependent derepression in neural progenitors. This produces a non-cell-autonomous migration defect in neighboring cells. The branch should be curated as secondary Reelin-pathway involvement within a PI3K-AKT-mTOR disease skeleton unless Reelin misexpression is the central causal mechanism of the entry.
Downstream
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Terminal Somal Translocation Failure
Show evidence (3 references)
"Within human FMCD-affected brain, we found that cells showing activation of the PI3K-AKT-mTOR pathway were enriched for the AKT3(E17K) mutation."
Human focal cortical malformation tissue links mosaic AKT3 activation to the broader focal malformation context.
"Mutation-expressing neural progenitors showed misexpression of reelin, which led to a non-cell autonomous migration defect in neighboring cells, due at least in part to derepression of reelin transcription in a manner dependent on the forkhead box (FOX) transcription factor FOXG1."
Supports the secondary AKT3-FOXG1-Reelin branch and its non-cell-autonomous migration effect.
"Treatments aimed at either blocking downstream AKT signaling or inactivating reelin restored migration."
Functional rescue supports Reelin misexpression as a causal branch downstream of AKT3/FOXG1 perturbation.