An ankyrin-binding motif regulates nuclear levels of L1-type neuroglian and expression of the oncogene Myc in Drosophila neurons.

L1 cell adhesion molecule (L1CAM) is well-known for its importance in nervous system development and cancer progression. In addition to its role as a plasma membrane protein in cytoskeletal organization, recent in vitro studies have revealed that both transmembrane and cytosolic fragments of proteolytically cleaved vertebrate L1CAM translocate to the nucleus. In vitro studies indicate that nuclear L1CAM affects genes with functions in DNA post-replication repair, cell cycle control, and cell migration and differentiation, but its in vivo role and how its nuclear levels are regulated is less well-understood. Here, we report that mutations in the conserved ankyrin-binding domain affect nuclear levels of the sole Drosophila homolog neuroglian (Nrg) and that it also has a noncanonical role in regulating transcript levels of the oncogene Myc in the adult nervous system. We further show that altered nuclear levels of Nrg correlate with altered transcript levels of Myc in neurons, similar to what has been reported for human glioblastoma stem cells. However, whereas previous in vitro studies suggest that increased nuclear levels of L1CAM promote tumor cell survival, we found here that elevated levels of nuclear Nrg in neurons are associated with increased sensitivity to oxidative stress and reduced life span of adult animals. We therefore conclude that these findings are of potential relevance to the management of neurodegenerative diseases associated with oxidative stress and cancer.

Input-specific regulation of hippocampal circuit maturation by non-muscle myosin IIB.

Myh9 and Myh10, which encode two major isoforms of non-muscle myosin II expressed in the brain, have emerged as risk factors for developmental brain disorders. Myosin II motors regulate neuronal cytoskeletal dynamics leading to optimization of synaptic plasticity and memory formation. However, the role of these motor complexes in brain development remains poorly understood. Here, we disrupted the in vivo expression of Myh9 and/or Myh10 in developing hippocampal neurons to determine how these motors contribute to circuit maturation in this brain area important for cognition. We found that Myh10 ablation in early postnatal, but not mature, CA1 pyramidal neurons reduced excitatory synaptic function in the Schaffer collateral pathway, whereas more distal inputs to CA1 neurons were relatively unaffected. Myh10 ablation in young neurons also selectively impaired the elongation of oblique dendrites that receive Schaffer collateral inputs, whereas the structure of distal dendrites was normal. We observed normal spine density and spontaneous excitatory currents in these neurons, indicating that Myh10 KO impaired proximal pathway synaptic maturation through disruptions to dendritic development rather than post-synaptic strength or spine morphogenesis. To address possible redundancy and/or compensation by other Myosin II motors expressed in neurons, we performed similar experiments in Myh9 null neurons. In contrast to findings in Myh10 mutants, evoked synaptic function in young Myh9 KO hippocampal neurons was normal. Data obtained from double Myh9/Myh10 KO neurons largely resembled the MyH10 KO synaptic phenotype. These data indicate that Myosin IIB is a key molecular factor that guides input-specific circuit maturation in the developing hippocampus. Non-muscle myosin II is an actin binding protein with three isoforms in the brain (IIA, IIB and IIC) encoded by the myh9, myh10, and myh14 genes in mice, respectively. We have studied the structure and the function of hippocampal CA1 neurons missing NMIIB and/or NMIIA proteins at different times during development. We have discovered that NMIIB is the major isoform regulating Schaffer collateral inputs, and that this regulation is restricted to early postnatal development.

Kv7 potassium channels in airway smooth muscle cells: signal transduction intermediates and pharmacological targets for bronchodilator therapy.

Expression and function of Kv7 (KCNQ) voltage-activated potassium channels in guinea pig and human airway smooth muscle cells (ASMCs) were investigated by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), patch-clamp electrophysiology, and precision-cut lung slices. qRT-PCR revealed expression of multiple KCNQ genes in both guinea pig and human ASMCs. Currents with electrophysiological and pharmacological characteristics of Kv7 currents were measured in freshly isolated guinea pig and human ASMCs. In guinea pig ASMCs, Kv7 currents were significantly suppressed by application of the bronchoconstrictor agonists methacholine (100 nM) or histamine (30 µM), but current amplitudes were restored by addition of a Kv7 channel activator, flupirtine (10 µM). Kv7 currents in guinea pig ASMCs were also significantly enhanced by another Kv7.2-7.5 channel activator, retigabine, and by celecoxib and 2,5-dimethyl celecoxib. In precision-cut human lung slices, constriction of airways by histamine was significantly reduced in the presence of flupirtine. Kv7 currents in both guinea pig and human ASMCs were inhibited by the Kv7 channel blocker XE991. In human lung slices, XE991 induced robust airway constriction, which was completely reversed by addition of the calcium channel blocker verapamil. These findings suggest that Kv7 channels in ASMCs play an essential role in the regulation of airway diameter and may be targeted pharmacologically to relieve airway hyperconstriction induced by elevated concentrations of bronchoconstrictor agonists.