Molecular diversity of surface receptors has been hypothesized to provide a mechanism for selective synaptic connectivity. Neurexins are highly diversified receptors that drive the morphological and functional differentiation of synapses. Using a single cDNA sequencing approach, we detected 1,364 unique neurexin-α and 37 neurexin-β mRNAs produced by alternative splicing of neurexin pre-mRNAs. This molecular diversity results from near-exhaustive combinatorial use of alternative splice insertions in Nrxn1α and Nrxn2α. By contrast, Nrxn3α exhibits several highly stereotyped exon selections that incorporate novel elements for posttranscriptional regulation of a subset of transcripts. Complexity of Nrxn1α repertoires correlates with the cellular complexity of neuronal tissues, and a specific subset of isoforms is enriched in a purified cell type. Our analysis defines the molecular diversity of a critical synaptic receptor and provides evidence that neurexin diversity is linked to cellular diversity in the nervous system.

The "band heterotopia" or "double cortex" is a brain anomaly that is presumed to result from a premature arrest of neuronal migration. Patients with this anomaly are reported to have a variable clinical course that has been, heretofore, unpredictable. The clinical records and magnetic resonance (MR) imaging studies of 27 patients with band heterotopia were retrospectively reviewed in an attempt to determine whether imaging findings are useful in predicting clinical outcome of affected patients. Statistical analyses revealed the following correlations: (1) severity of T2 prolongation in the brain with motor delay (p = 0.03); (2) degree of ventricular enlargement with the age of seizure onset (p = 0.04), and with development and intelligence (p = 0.04); (3) severity of pachygyria with the age of seizure onset (p = 0.01), seizure type (p = 0.03), and an abnormal neurologic examination (p = 0.002); (4) parietal involvement with delayed speech development (p = 0.05); (5) occipital involvement with age of seizure onset (p = 0.006); (6) age of seizure onset with development and intelligence (p = 0.03) and with an abnormal neurologic examination (p = 0.04); and (7) severity of the pachygyria and thickness of band with development of symptomatic generalized epilepsy (p = 0.002 and p = 0.02, respectively) and Lennox-Gastaut syndrome (p = 0.002 and p = 0.01, respectively).

One of the most challenging areas in nosology is in the field of severe generalized epilepsy of early childhood. This is certainly true in the case of Lennox-Gastaut syndrome (LGS), an age-related epileptogenic encephalopathy which comprises several types of generalized seizures including tonic seizures, atypical absence seizures and frequent status epilepticus. EEG shows generalized slow spike waves, and as the disease progresses, cognitive functions deteriorate. LGS is listed in the 1989 classification of the International League Against Epilepsy alongside epilepsy with myoclonic astatic seizures and West's syndrome. A number of variants or atypical forms have been proposed. As a result, differential diagnosis presents a major challenge and includes specific generalized epilepsies, i.e., metabolic or inflammatory; secondarily generalized epilepsies, i.e., those arising from the frontal lobe; and severe forms of idiopathic generalized epilepsy, i.e., Doose syndrome. Antiepileptic drug (AED) treatment of LGS has been disappointing. Results obtained from anterior callosotomy have been promising, but only a small number of patients have been evaluated. Although the syndrome is rare, the severe nature and intractability of LGS emphasizes the need for the development of specific AEDs which would completely modify the quality of life for these patients.

Alternative RNA splicing represents a central mechanism for expanding the coding power of genomes. Individual RNA-binding proteins can control alternative splicing choices in hundreds of RNA transcripts, thereby tuning amounts and functions of large numbers of cellular proteins. We found that the RNA-binding protein SLM2 is essential for functional specification of glutamatergic synapses in the mouse hippocampus. Genome-wide mapping revealed a markedly selective SLM2-dependent splicing program primarily consisting of only a few target messenger RNAs that encode synaptic proteins. Genetic correction of a single SLM2-dependent target exon in the synaptic recognition molecule neurexin-1 was sufficient to rescue synaptic plasticity and behavioral defects in Slm2 knockout mice. These findings uncover a highly selective alternative splicing program that specifies synaptic properties in the central nervous system.

The unique anatomical and functional features of principal and interneuron populations are critical for the appropriate function of neuronal circuits. Cell type-specific properties are encoded by selective gene expression programs that shape molecular repertoires and synaptic protein complexes. However, the nature of such programs, particularly for post-transcriptional regulation at the level of alternative splicing is only beginning to emerge. We here demonstrate that transcripts encoding the synaptic adhesion molecules neurexin-1,2,3 are commonly expressed in principal cells and interneurons of the mouse hippocampus but undergo highly differential, cell type-specific alternative splicing. Principal cell-specific neurexin splice isoforms depend on the RNA-binding protein Slm2. By contrast, most parvalbumin-positive (PV+) interneurons lack Slm2, express a different neurexin splice isoform and co-express the corresponding splice isoform-specific neurexin ligand Cbln4. Conditional ablation of Nrxn alternative splice insertions selectively in PV+ cells results in elevated hippocampal network activity and impairment in a learning task. Thus, PV-cell-specific alternative splicing of neurexins is critical for neuronal circuit functionDOI: http://dx.doi.org/10.7554/eLife.22757.001

Rat fetal lung is a target tissue for 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25 (OH)2 D3]. We have identified the cells that respond to the hormone and tested the hypothesis that the lung is also a source of 1 alpha,25(OH)2D3. We found that 1) at the end of pregnancy (days 20-21) alveolar type II cells (ATII) bore 1 alpha,25(OH)2D3 receptors and responded to the hormone. Incubating these cells with 10(-9) M 1 alpha,25(OH)2D3 for 48 h stimulated the synthesis (87.3 +/- 9.1%) and release (61.7 +/- 6.1%) of disaturated phosphatidylcholine; 2) EB-1213, a 1 alpha,25(OH)2D3 analogue with low calcemic activity, had similar effects on ATII; 3) neither fetal lung fibroblasts nor neonatal ATII (day 2 postpartum) expressed 1 alpha,25(OH)2D3 receptors; and 4) in contrast, fetal lung fibroblasts taken on days 19-22 of gestation converted [3H]25(OH)D3 to [3H]1 alpha,25(OH)2D3, whereas ATII and skin fibroblasts did not. These findings suggest that 1 alpha,25(OH)2D3 is a local mediator of epithelial-mesenchymal cell interactions in the developing rat lung and that 1 alpha,25(OH)2D3 or EB-1213 might be therapeutically useful in treating the respiratory distress syndrome of premature neonates.

ABSTRACT

If both rapid and genomic pathways may co-exist in the same cell, the involvement of the nuclear vitamin D receptor (VDR) in the rapid effects of 1,25-dihydroxyvitamin D 3 (1,25-(OH) 2 D 3 ) remains unclear. We therefore studied rapid and long term effects of 1,25-(OH) 2 D 3 in cultured skin fibroblasts from three patients with severe vitamin D-resistant rickets and one age-matched control. Patients bear homozygous missense VDR mutations that abolished either VDR binding to DNA (patient 1, mutation K45E) or its stable ligand binding (patients 2 and 3, mutation W286R). In patient 1 cells, 1,25-(OH) 2 D 3 (1 pM-10 nM) had no effect on either intracellular calcium or 24-hydroxylase (enzyme activity and mRNA expression). In contrast, cells bearing the W286R mutation had calcium responses to 1,25-(OH) 2 D 3 (profile and magnitude) and 24-hydroxylase responses to low (1 pM-100 pM) 1,25-(OH) 2 D 3 concentrations (activity, CYP24, and ferredoxin mRNAs) similar to those of controls. The blocker of Ca 2؉ channels, verapamil, impeded both rapid (calcium) and long term (24-hydroxylase activity, CYP24, and ferredoxin mRNAs) responses in patient and control fibroblasts. The MEK 1/2 kinase inhibitor PD98059 also blocked the CYP24 mRNA response. Taken together, these results suggest that 1,25-(OH) 2 D 3 rapid effects require the presence of VDR and control, in part, the first step of 1,25-(OH) 2 D 3 catabolism via increased mRNA expression of the CYP24 and ferredoxin genes in the 24-hydroxylase complex.The general and severe end organ resistance to vitamin D observed in patients with mutations in the gene encoding the nuclear vitamin D receptor (VDR) 1 bring forth strong evidence that most cellular actions of 1,25-(OH) 2 D 3 , the hormonal form of vitamin D, are mediated through interactions of the hormone with its nuclear receptor (1). The VDR, which belongs to the steroid/thyroid nuclear receptor family, is composed of two principal domains, one domain for hormone binding (exons 6 -9) and one domain for DNA binding (exons 2 and 3, coding for two zinc fingers) (2). Although most classical effects of 1,25-(OH) 2 D 3 involve this genomic pathway, several other effects may be observed very rapidly, within seconds to minutes, and are not blocked by inhibitors of transcription or translation, suggesting a more direct action of the hormone at the membrane level (3-7). These effects include activation of the phospholipase C pathway via G␣ q/11 (8, 9), activation of the adenylate cyclase pathway (10), opening of voltage-gated Ca 2ϩ channels (L-type) in the plasma membrane (11, 12), Ca 2ϩ mobilization from the endoplasmic reticulum (5), and an increase in cyclic guanosine monophosphate levels (13). The rapid effects of 1,25-(OH) 2 D 3 also include the activation of the mitogenactivated protein kinase (MAPK) pathway (14 -16), which induces a cross-talk with the cell nucleus via phosphorylation of cytoplasmic kinases and nuclear transcription factors (7,16,17).Attempts have been made to identify the receptor mediating the non-classical r...