Toward a Broader View of Ube3a in a Mouse Model of Angelman Syndrome: Expression in Brain,Spinal Cord,Sciatic Nerve and Glial Cells

Angelman Syndrome (AS) is a devastating neurodevelopmental disorder characterized by developmental delay, speech impairment, movement disorder, sleep disorders and refractory epilepsy. AS is caused by loss of the Ube3a protein encoded for by the imprinted Ube3a gene. Ube3a is expressed nearly exclusively from the maternal chromosome in mature neurons. While imprinting in neurons of the brain has been well described, the imprinting and expression of Ube3a in other neural tissues remains relatively unexplored. Moreover, given the overwhelming deficits in brain function in AS patients, the possibility of disrupted Ube3a expression in the infratentorial nervous system and its consequent disability have been largely ignored. We evaluated the imprinting status of Ube3a in the spinal cord and sciatic nerve and show that it is also imprinted in these neural tissues. Furthermore, a growing body of clinical and radiological evidence has suggested that myelin dysfunction may contribute to morbidity in many neurodevelopmental syndromes. However, findings regarding Ube3a expression in non-neuronal cells of the brain have varied. Utilizing enriched primary cultures of oligodendrocytes and astrocytes, we show that Ube3a is expressed, but not imprinted in these cell types. Unlike many other neurodevelopmental disorders, AS symptoms do not become apparent until roughly 6 to 12 months of age. To determine the temporal expression pattern and silencing, we analyzed Ube3a expression in AS mice at several time points. We confirm relaxed imprinting of Ube3a in neurons of the postnatal developing cortex, but not in structures in which neurogenesis and migration are more complete. This furthers the hypothesis that the apparently normal window of development in AS patients is supported by an incompletely silenced paternal allele in developing neurons, resulting in a relative preservation of Ube3a expression during this crucial epoch of early development.     

Association of AFF1 rs340630 and AFF3 rs10865035 polymorphisms with systemic lupus erythematosus in a Chinese population

The aim of this study was to evaluate whether two single-nucleotide polymorphisms (SNPs), AF4/FMR2 family, member 1 (AFF1) rs340630 and AF4/FMR2 family, member 3 (AFF3) rs10865035, show significant evidence for association with systemic lupus erythematosus (SLE) in a Chinese population. A total of 868 Chinese patients with SLE and 975 geographically and ethnically matched healthy control subjects were enrolled in the current study. The genotypes of these two SNPs were determined by Sequenom MassArray technology. Significant evidence for association of AFF3 rs10865035 with SLE was detected (for A versus G, P?=?4.81?×?10^?4, odds ratio (OR) 1.26, 95?% confidence interval (95 %CI) 1.11–1.44). However, no association between AFF1 rs340630 and SLE was found in the Chinese population (for A versus G, P?=?0.79, OR 0.98, 95 %CI 0.86–1.12). No significant evidence for association of AFF3 rs10865035 polymorphism with any clinical features was detected. By targeting a variant with convincing evidence for association with rheumatoid arthritis, significant association of AFF3 rs10865035 with SLE was detected in the Chinese population, indicating that AFF3 might be a common autoimmunity gene. Further case-control studies based on larger sample sizes in diverse ethnic populations are required to clarify the role of AFF1 rs340630 in SLE.     

Characterization of teleost Mdga1 using a gene‐trap approach in medaka (Oryzias latipes)

MAM domain containing glycosilphosphatidilinositol anchor 1 (MDGA1) is an IgCAM protein present in many vertebrate species including humans. In mammals, MDGA1 is expressed by a subset of neurons in the developing brain and thought to function in neural cell migration. We identified a fish ortholog of mdga1 by a gene‐trap screen utilizing the Frog Prince transposon in medaka (Japanese killifish, Oryzias latipes). The gene‐trap vector was inserted into an intronic region of mdga1 to form a chimeric protein with green fluorescent protein, allowing us to monitor mdga1 expression in vivo. Expression of medaka mdga1 was seen in various types of embryonic brain neurons, and specifically in neurons migrating toward their target sites, supporting the proposed function of MDGA1. We also isolated the closely related mdga2 gene, whose expression partially overlapped with that of mdga1. Despite the fact that the gene‐trap event eliminated most of the functional domains of the Mdga1 protein, homozygous embryos developed normally without any morphological abnormality, suggesting a functional redundancy of Mdga1 with other related proteins. High sequential homology of MDGA proteins between medaka and other vertebrate species suggests an essential role of the MDGA gene family in brain development among the vertebrate phylum. genesis 47:505–513, 2009. © 2009 Wiley‐Liss, Inc.     

Mutation of the Variant α-Tubulin TUBA8 Results in Polymicrogyria with Optic Nerve Hypoplasia

The critical importance of cytoskeletal function for correct neuronal migration during development of the cerebral cortex has been underscored by the identities of germline mutations underlying a number of human neurodevelopmental disorders. The proteins affected include TUBA1A, a major α-tubulin isoform, and microtubule-associated components such as doublecortin, and LIS1. Mutations in these genes are associated with the anatomical abnormality lissencephaly, which is believed to reflect failure of neuronal migration. An important recent observation has been the dependence of cortical neuronal migration upon acetylation of α-tubulin at lysine 40 by the histone acetyltransferase Elongator complex. Here, we describe a recognizable autosomal recessive syndrome, characterized by generalized polymicrogyria in association with optic nerve hypoplasia (PMGOH). By autozygosity mapping, we show that the molecular basis for this condition is mutation of the TUBA8 gene, encoding a variant α-tubulin of unknown function that is not susceptible to the lysine 40 acetylation that regulates microtubule function during cortical neuron migration. Together with the unique expression pattern of TUBA8 within the developing cerebral cortex, these observations suggest a role for this atypical microtubule component in regulating mammalian brain development.