The PAR Polarity Complex and Cerebellar Granule Neuron Migration
CELLULAR AND MOLECULAR CONTROL OF NEURONAL MIGRATION
Authors: Ramahi, Joseph S.; Solecki, David J.
Abstract
Proper migration of neurons is one of the most important aspects of early brain development. After neuronal progenitors are born in their respective germinal niches, they must migrate to their final locations to form precise neural circuits. A majority of migrating neurons move by associating and disassociating with glial fibers, which serve as scaffolding for the developing brain. Cerebellar granule neurons provide a model system for examination of the mechanisms of neuronal migration in dissociated and slice culture systems; the ability to purify these cells allows migration assays to be paired with genetic, molecular, and biochemical findings. CGNs migrate in a highly polarized fashion along radial glial fibers, using a two-stroke nucleokinesis cycle. The PAR polarity complex of PARD3, PARD6, and an atypical protein kinase C (aPKC) regulate several aspects of neuronal migration. The PAR polarity complex regulates the coordinated movements of the centrosome and soma during nucleokinesis, and also the stability of the microtubule cytoskeleton during migration. PAR proteins coordinate actomyosin dynamics in the leading process of migrating neurons, which are required for migration. The PAR complex also controls the cell-cell adhesions made by migrating neurons along glial cells, and through this mechanism regulates germinal zone exit during prenatal brain development. These findings suggest that the PAR complex coordinates the movement of multiple cellular elements as neurons migrate and that further examination of PAR complex effectors will not only provide novel insights to address fundamental challenges to the field but also expand our understanding of how the PAR complex functions at the molecular level.
Associations with tight junction genes PARD3 and MAGI2 in Dutch patients point to a common barrier defect for coeliac disease and ulcerative colitis
GUT
Authors: Wapenaar, M. C.; Monsuur, A. J.; van Bodegraven, A. A.; Weersma, R. K.; Bevova, M. R.; Linskens, R. K.; Howdle, P.; Holmes, G.; Mulder, C. J.; Dijkstra, G.; van Heel, D. A.; Wijmenga, C.
Abstract
Background: Coeliac disease (gluten-sensitive enteropathy; GSE) and inflammatory bowel disease (IBD) are common gastrointestinal disorders. Both display enhanced intestinal permeability, initiated by gluten exposure (GSE) or bacterial interactions (IBD). Previous studies showed the association of both diseases with variants in MYO9B, presumably involved in epithelial permeability. Aim: It was hypothesised that genetic variants in tight junction genes might affect epithelial barrier function, thus contributing to a shared pathogenesis of GSE and IBD. Methods: This hypothesis was tested with a comprehensive genetic association analysis of 41 genes from the tight junction pathway, represented by 197 tag single nucleotide polymorphism (SNP) markers. Results: Two genes, PARD3 (two SNPs) and MAGI2 (two SNPs), showed weak association with GSE in a Dutch cohort. Replication in a British GSE cohort yielded significance for one SNP in PARD3 and suggestive associations for two additional SNPs, one each in PARD3 and MAGI2. Joint analysis of the British and Dutch data further substantiated the association for both PARD3 (rs10763976, p= 6.4x10(-5); OR 1.23, 95% CI 1.11 to 1.37) and MAGI2 (rs6962966, p= 7.6x10(-4); OR 1.19, 95% CI 1.08 to 1.32). Association was also observed in Dutch ulcerative colitis patients with MAGI2 ( rs6962966, p= 0.0036; OR 1.26, 95% CI 1.08 to 1.47), and suggestive association with PARD3 (rs4379776, p= 0.068). Conclusions: These results suggest that coeliac disease and ulcerative colitis may share a common aetiology through tight junction-mediated barrier defects, although the observations need further replication.