N-WASp is required for Schwann cell cytoskeletal dynamics, normal myelin gene expression and peripheral nerve myelination.

Schwann cells elaborate myelin sheaths around axons by spirally wrapping and compacting their plasma membranes. Although actin remodeling plays a crucial role in this process, the effectors that modulate the Schwann cell cytoskeleton are poorly defined. Here, we show that the actin cytoskeletal regulator, neural Wiskott-Aldrich syndrome protein (N-WASp), is upregulated in myelinating Schwann cells coincident with myelin elaboration. When N-WASp is conditionally deleted in Schwann cells at the onset of myelination, the cells continue to ensheath axons but fail to extend processes circumferentially to elaborate myelin. Myelin-related gene expression is also severely reduced in the N-WASp-deficient cells and in vitro process and lamellipodia formation are disrupted. Although affected mice demonstrate obvious motor deficits these do not appear to progress, the mutant animals achieving normal body weights and living to advanced age. Our observations demonstrate that N-WASp plays an essential role in Schwann cell maturation and myelin formation.

Specific Role for GSK3α in Limiting Long-Term Potentiation in CA1 Pyramidal Neurons of Adult Mouse Hippocampus.

Glycogen synthase kinase-3 (GSK3) mediates phosphorylation of several hundred proteins, and its aberrant activity is associated with an array of prevalent disorders. The two paralogs, GSK3α and GSK3ß, are expressed ubiquitously and fulfill common as well as unique tasks throughout the body. In the CNS, it is established that GSK3 is involved in synaptic plasticity. However, the relative roles of GSK3 paralogs in synaptic plasticity remains controversial. Here, we used hippocampal slices obtained from adult mice to determine the role of each paralog in CA3-CA1 long-term potentiation (LTP) of synaptic transmission, a form of plasticity critically required in learning and memory. Conditional Camk2a Cre-driven neuronal deletion of the Gsk3a gene, but not Gsk3b, resulted in enhanced LTP. There were no changes in basal synaptic function in either of the paralog-specific knockouts, including several measures of presynaptic function. Therefore, GSK3α has a specific role in serving to limit LTP in adult CA1, a postsynaptic function that is not compensated by GSK3ß.

Mammalian diaphanous-related formin 1 regulates GSK3ß-dependent microtubule dynamics required for T cell migratory polarization.

The mammalian diaphanous-related formin (mDia1), a Rho-regulated cytoskeletal modulator, has been shown to promote T lymphocyte chemotaxis and interaction with antigen presenting cells, but the mechanisms underpinning mDia1 roles in these processes have not been defined. Here we show that mDia1(-/-) T cells exhibit impaired lymphocyte function-associated antigen 1 (LFA-1)-mediated T cell adhesion, migration and in vivo trafficking. These defects are associated with impaired microtubule (MT) polarization and stabilization, altered MT dynamics and reduced peripheral clustering of the MT plus-end-protein, adenomatous polyposis coli (APC) in migrating T cells following LFA-1-engagement. Loss of mDia1 also leads to impaired inducible inactivation of the glycogen synthase kinase (GSK) 3ß as well as hyperphosphorylation and reduced levels of APC in migrating T cells. These findings identify essential roles for the mDia1 formin in modulating GSK3ß-dependent MT contributions to induction of T-cell polarity, adhesion and motility.

Analysis of hindbrain patterning defects caused by the kreisler(enu) mutation reveals multiple roles of Kreisler in hindbrain segmentation.

The embryonic hindbrain is subdivided into eight subunits, termed rhombomeres (r1-r8). The Kreisler (Krml1/MafB/val) transcription factor is expressed in and essential for patterning rhombomeres 5 and 6. Here, we have shown that in the chemically induced kreisler(enu) (kr(enu)) allele, a point mutation in the DNA binding domain abolishes or severely reduces Kreisler-dependent transcription. Comparison of kr(enu)/kr(enu) embryos with those homozygous for the classic kreisler (kr) mutation has reconciled past discrepancies and revealed multiple roles of Kreisler in hindbrain segmentation. These analyses demonstrate that Kreisler is required for maintenance and expansion but not initiation of the Krox20 expressing r5 domain. The differences in the "r5-like" phenotype of kr(enu)/kr(enu) and kr/kr mouse embryos, and zebrafish carrying mutations in the Kreisler orthologue valentino (val) suggest that Kreisler performs many of its r5-specific functions by associating with other proteins. By contrast, kr/kr and kr(enu)/kr(enu) mouse and val-/- zebrafish embryos all exhibit indistinguishable defects in r6 specification. Thus, transcriptionally active Kreisler is required for r6 specification. Unlike mouse kr(enu)/kr(enu) and zebrafish val-/- embryos, kr/kr embryos exhibited anterior defects. We determined that the kr chromosomal inversion caused ectopic Kreisler expression in r3 of kr/kr and kr/+ embryos. Hence, Kreisler regulates maintenance and expansion of r5 and specification of r6 but is not required for r3 development.

The mouse Kreisler (Krml1/MafB) segmentation gene is required for differentiation of glomerular visceral epithelial cells.

Molecular components of the glomerular filtration mechanism play critical roles in renal diseases. Many of these components are produced during the final stages of differentiation of glomerular visceral epithelial cells, also known as podocytes. While basic domain leucine zipper (bZip) transcription factors of the Maf subfamily have been implicated in cellular differentiation processes, Kreisler (Krml1/MafB), the gene affected in the mouse kreisler (kr) mutation, is known for its role in hindbrain patterning. Here we show that mice homozygous for the kr(enu) mutation develop renal disease and that Kreisler is essential for cellular differentiation of podocytes. Consistent with abnormal podocyte differentiation, kr(enu) homozygotes show proteinuria, and fusion and effacement of podocyte foot processes, which are also observed in the nephrotic syndrome. Kreisler acts during the final stages of glomerular development-the transition between the capillary loop and mature stages-and downstream of the Pod1 basic domain helix-loop-helix transcription factor. The levels of Podocin, the gene mutated in autosomal recessive steroid-resistant nephrotic syndrome (NPHS2), and Nephrin, the gene mutated in congenital nephrotic syndrome of the Finnish type (NPHS1), are slightly reduced in kr(enu)/kr(enu) podocytes. However, these observations alone are unlikely to account for the aberrant podocyte foot process formation. Thus, Kreisler must regulate other unknown genes required for podocyte function and with possible roles in kidney disease.