Mutant Schwann cells fail to downregulate Oct-6. Whole embryo sections at E17.5 and longitudinal sciatic nerve sections at P3 were stained for Oct-6 (green) and laminin gamma-1 (red), and images were merged. E17.5 embryo sections were stained for neurofilament (blue) to identify nerves. These images indiate that initiation of Oct-6 does not require laminin gamma-1.

Laminin, an extracellular matrix protein, is required for peripheral nerve myelination. Laminin is a hetero-trimeric glycoprotein composed of α-, β-, and γ-chains. Mutations in laminin a2, a subunit of laminin-2 (a2/b1/g1; the major laminin isoform expressed in the PNS and muscle), not only cause muscular dystrophy but also peripheral nerve dysmyelination.  Laminin γ1 is one of the most abundant chains and is present in all known laminin isoforms expressed in the PNS.

To study the mechanism of laminin function in PNS development, members of the Strickland Laboratory specifically disrupted the laminin γ1 gene in Schwann cells at early developmental stages using the myelin protein zero promoter to drive Cre expression (P0/Cre:fLAMγ1 mice). In the absence of laminin, Schwann cells fail to undergo radial sorting of axons, arrest at the immature Schwann cell stage, and do not develop into myelinating Schwann cells.  The impaired axon/ Schwann cell interaction prevents phosphorylation of β-neuregulin-1 receptors and results in decreased cell proliferation. Postnatally, laminin-deficient Schwann cells exhibit reduced PI3-kinase activity and activation of caspase cascades, leading to apoptosis.

Currently, postdoc Wei-Ming Yu of the Strickland Lab is exploring the downstream mechanisms by which laminin mediates radial sorting and ensheathment of axons using a mouse Schwann cell/dorsal root ganglion (SC/DRG) neuronal co-culture system. Electron and confocal microscopic analysis revealed that Schwann cells from co-cultures lacking laminin had short filapodia extensions and did not form bipolar morphology. To investigate how laminins affect Schwann cell actin cytoskeleton during ensheathment, we co-infected SC/DRG neuronal co-cultures with recombinant adenoviruses expressing eGFP-tagged actin and mCherry-tagged neurofilament light chain. Dual-channel live cell imaging will be performed in these co-infected co-cultures, and laminin regulation of actin cytoskeleton during ensheathment and myelination will be monitored.

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