β2 and γ3 laminins are critical cortical basement membrane components: Ablation of Lamb2 and Lamc3 genes disrupts cortical lamination and produces dysplasia

Abstract

Cortical development is dependent on the timely production and migration of neurons from neurogenic sites to their mature positions. Mutations in several receptors for extracellular matrix (ECM) molecules and their downstream signaling cascades produce dysplasia in brain. Although mutation of a critical binding site in the gene that encodes the ECM molecule laminin γ1 (Lamc1) disrupts cortical lamination, the ECM ligand(s) for many ECM receptors have not been demonstrated directly in the cortex. Several isoforms of the heterotrimeric laminins, all containing the β2 and γ3 chain, have been isolated from the brain, suggesting they are important for CNS function. Here, we report that mice homozygous null for the laminin β2 and γ3 chains exhibit cortical laminar disorganization. Mice lacking both of these laminin chains exhibit hallmarks of human cobblestone lissencephaly (type II, nonclassical): they demonstrate severe laminar disruption; midline fusion; perturbation of Cajal-Retzius cell distribution; altered radial glial cell morphology; and ectopic germinal zones. Surprisingly, heterozygous mice also exhibit laminar disruption of cortical neurons, albeit with lesser severity. In compound null mice, the pial basement membrane is fractured, and the distribution of a key laminin receptor, dystroglycan, is altered. These data suggest that β2 and γ3-containing laminins play an important dose-dependent role in development of the cortical pial basement membrane, which serves as an attachment site for Cajal-Retzius and radial glial cells, thereby guiding neural development.

Cellular and Axonal Constituents of Neocortical Molecular Layer Heterotopia

“…Iba1-expressing microglia were present in heterotopia but microglial morphology did not indicate an activated phenotype (data not shown). In order to confirm these results, we examined primary histological material in our laboratory of brains of laminin β2/γ3 double-KO mice which develop numerous MLH throughout most of the neocortex [14]. Similar to our observations in C57BL/6J mice, we found that Iba1-expressing microglia were present in heterotopia in laminin β2/γ3 double-KO mice (data not shown).…”

“…MLH have also been observed in several knockout (KO) mice [14,15,16,17,18,19,20,21,22,23]. MLH in mice are indistinguishable from heterotopia observed in humans.…”

“…003782 [35]) bred in academic vivaria from founders obtained from The Jackson Laboratory, as previously described [36,37]. Laminin β2/γ3 double-KO mice were also examined, as well as laminin β2/γ3 double-KO mice crossed with Cx3Cr1/eGFP transgenic mice, as previously described [14]. The mice were housed in temperature-controlled facilities maintained between 20 and 22.5°C, with 12-hour light/dark cycles, in standard plastic cages (11.75 × 7.5 × 5 inches) with no more than 5 mice per cage, and with food and water available ad libitum.…”

Tissue mechanics regulate brain development, homeostasis and disease

“…Experimental disruption of ECM, ECM receptors and mechanosignaling proteins in neural cells can dramatically affect early brain development. For example, mutation of the subunits laminin β2 and laminin γ3 causes laminar disruption of the cortex (Radner et al, 2013), and mice lacking FAK in the dorsal forebrain also exhibit cortical lamination defects, neuronal dysplasia and abnormal synapse formation (Beggs et al, 2003;Rico et al, 2004). Although these studies represent manipulations of proteins involved in mechanosignaling, the resulting effects on cell adhesion could also directly contribute to the observed phenotypes.…”

Laminins containing the β2 and γ3 chains regulate astrocyte migration and angiogenesis in the retina

“…Goat anti-rabbit 488 and 568, goat anti-rat 488 and 568, donkey anti-rabbit 488 and 594, and donkey anti-rat 488 and 594 (Life Technologies, Grand Island, NY, USA) secondary antibodies were used. The specificity of the laminin antibodies has been published previously: anti-β2 (Pinzón-Duarte et al, 2010;Radner et al, 2013) and anti-γ3 antibodies (Li et al, 2012). The following laminins were used: EHS-laminin (Life Technologies), recombinant laminin-521 (BioLamina, Stockholm, Sweden) and laminin 5 (a gift from Dr Manuel Koch, Universität zu Köln, Germany).…”