Functional effects of spinocerebellar ataxia type 13 mutations are conserved in zebrafish Kv3.3 channels

<p>Abstract</p> <p>Background</p> <p>The zebrafish has been suggested as a model system for studying human diseases that affect nervous system function and motor output. However, few of the ion channels that control neuronal activity in zebrafish have been characterized. Here, we have identified zebrafish orthologs of voltage-dependent Kv3 (KCNC) K⁺channels. Kv3 channels have specialized gating properties that facilitate high-frequency, repetitive firing in fast-spiking neurons. Mutations in human Kv3.3 cause spinocerebellar ataxia type 13 (SCA13), an autosomal dominant genetic disease that exists in distinct neurodevelopmental and neurodegenerative forms. To assess the potential usefulness of the zebrafish as a model system for SCA13, we have characterized the functional properties of zebrafish Kv3.3 channels with and without mutations analogous to those that cause SCA13.</p> <p>Results</p> <p>The zebrafish genome (release Zv8) contains six Kv3 family members including two Kv3.1 genes (<it>kcnc1a </it>and <it>kcnc1b</it>), one Kv3.2 gene (<it>kcnc2</it>), two Kv3.3 genes (<it>kcnc3a </it>and <it>kcnc3b</it>), and one Kv3.4 gene (<it>kcnc4</it>). Both Kv3.3 genes are expressed during early development. Zebrafish Kv3.3 channels exhibit strong functional and structural homology with mammalian Kv3.3 channels. Zebrafish Kv3.3 activates over a depolarized voltage range and deactivates rapidly. An amino-terminal extension mediates fast, N-type inactivation. The <it>kcnc3a </it>gene is alternatively spliced, generating variant carboxyl-terminal sequences. The R335H mutation in the S4 transmembrane segment, analogous to the SCA13 mutation R420H, eliminates functional expression. When co-expressed with wild type, R335H subunits suppress Kv3.3 activity by a dominant negative mechanism. The F363L mutation in the S5 transmembrane segment, analogous to the SCA13 mutation F448L, alters channel gating. F363L shifts the voltage range for activation in the hyperpolarized direction and dramatically slows deactivation.</p> <p>Conclusions</p> <p>The functional properties of zebrafish Kv3.3 channels are consistent with a role in facilitating fast, repetitive firing of action potentials in neurons. The functional effects of SCA13 mutations are well conserved between human and zebrafish Kv3.3 channels. The high degree of homology between human and zebrafish Kv3.3 channels suggests that the zebrafish will be a useful model system for studying pathogenic mechanisms in SCA13.</p

Activity Dependent Protein Degradation Is Critical for the Formation and Stability of Fear Memory in the Amygdala

Protein degradation through the ubiquitin-proteasome system [UPS] plays a critical role in some forms of synaptic plasticity. However, its role in memory formation in the amygdala, a site critical for the formation of fear memories, currently remains unknown. Here we provide the first evidence that protein degradation through the UPS is critically engaged at amygdala synapses during memory formation and retrieval. Fear conditioning results in NMDA-dependent increases in degradation-specific polyubiquitination in the amygdala, targeting proteins involved in translational control and synaptic structure and blocking the degradation of these proteins significantly impairs long-term memory. Furthermore, retrieval of fear memory results in a second wave of NMDA-dependent polyubiquitination that targets proteins involved in translational silencing and synaptic structure and is critical for memory updating following recall. These results indicate that UPS-mediated protein degradation is a major regulator of synaptic plasticity necessary for the formation and stability of long-term memories at amygdala synapses

The proteasome controls presynaptic differentiation through modulation of an on-site pool of polyubiquitinated conjugates

Differentiation of the presynaptic terminal is a complex and rapid event that normally occurs in spatially specific axonal regions distant from the soma; thus, it is believed to be dependent on intra-axonal mechanisms. However, the full nature of the local events governing presynaptic assembly remains unknown. Herein, we investigated the involvement of the ubiquitin-proteasome system (UPS), the major degradative pathway, in the local modulation of presynaptic differentiation. We found that proteasome inhibition has a synaptogenic effect on isolated axons. In addition, formation of a stable cluster of synaptic vesicles onto a postsynaptic partner occurs in parallel to an on-site decrease in proteasome degradation. Accumulation of ubiquitinated proteins at nascent sites is a local trigger for presynaptic clustering. Finally, proteasome-related ubiquitin chains (K11 and K48) function as signals for the assembly of presynaptic terminals. Collectively, we propose a new axon-intrinsic mechanism for presynaptic assembly through local UPS inhibition. Subsequent on-site accumulation of proteins in their polyubiquitinated state triggers formation of presynapses.info:eu-repo/semantics/publishedVersio

UBA1: At the Crossroads of Ubiquitin Homeostasis and Neurodegeneration

Neurodegenerative diseases are a leading cause of disability and early death. A common feature of these conditions is disruption of protein homeostasis. Ubiquitin-like modifier activating enzyme 1 (UBA1), the E1 ubiquitin-activating enzyme, sits at the apex of the ubiquitin cascade and represents an important regulator of cellular protein homeostasis. Critical contributions of UBA1-dependent pathways to the regulation of homeostasis and degeneration in the nervous system are emerging, including specific disruption of UBA1 in spinal muscular atrophy (SMA) and Huntington's disease (HD). In this review we discuss recent findings that put UBA1 at the centre of cellular homeostasis and neurodegeneration, highlighting the potential for UBA1 to act as a promising therapeutic target for a range of neurodegenerative diseases

Exit strategy for a founder dependent company. How to overcome the challenges and maximize the value of the company.

The objective of this research was to examine what are factors that drive the value in a young, small, founder dependent company and how can this be maximized in the projection of a potential exit of the founder. The research methodology followed the method of the case study as presented by Yin (2009), and was based on a single case study. Academic literature was used to build a base of information and a framework through which analyze the data collected through interviews in the case company. The company used for this case study is a Finnish SME, that imports and distributes food and beverage products in Finland. My findings suggest that understanding how resources are used, and what capabilities are developed in a young, small, founder-dependent company are crucial factors to understand its value, as they reveal if the company's can enjoy a competitive advantage over the other firms operating in the same market, and if this competitive advantage can be sustainable. They suggest that, even though the value of a founder-dependent company is inversely proportional to its degree of dependency on the founder, this dependence can be minimized in order to maximize the value of the company. The case company detains a good position in terms of resources and capabilities that guarantee it a sustained competitive advantage and, thus, a good value. However, it need to implement a number of steps in order to minimize its dependency over its founder, and consequently maximize its value

CATALOGO DEGLI OLOTIPI DEPOSITATI PRESSO IL MUSEO Dl PALEONTOLOGIA Dipartimento di Scienze della Terra Università degli Studi di Milano

&nbsp; &nbsp; &nbsp; Viene dato l'elenco degli "Olotipi" fino ad ora presenti nelle collezioni del Museo di Paleontologia — Dipartimento di Scienze della Terra — Universita degli Studi di Milano. Nel catalogo per ogni entità tassonomica sono indicati: &nbsp;nome del genere secondo la designazione originale &nbsp;nome della specie &nbsp;nome dell'autore della specie &nbsp;data di pubblicazione &nbsp;citazione bibliografica completa del lavoro con riferimento alla descrizione e all'illustrazione originale dell'olotipo &nbsp;eta &nbsp;ubicazione geografica precisa &nbsp;numero d'inventario ed indicazione della collezione originale

CATALOGO DEGLI OLOTIPI DEPOSITATI PRESSO IL LABORATORIO Dl MICROPALEONTOLOGIA Dipartimento di Scienze della Terra Università degli Studi di Milano

Il Laboratorio di Micropaleontologia — Dipartimento Scienze della Terra &nbsp;Università degli Studi di Milano vanta una ricca collezione di microfossili di particolare valore scientifico per la presenza di un numero cospicuo di olotipi dei quali viene dato l'elenco