hCMV and Tet promoters for inducible gene expression in rat neurons in vitro and in vivo

ESCRT Proteins Control the Dendritic Morphology of Developing and Mature Hippocampal Neurons

The proper shape of dendritic arbors of different types of neurons determines their proper communication within neuronal networks. The shape of dendritic arbors is acquired during a complex and multistep process called dendritogenesis. In most cases, once proper morphology is achieved, it remains stable throughout the lifespan, with the exception of rare events during which dendrites are abruptly pruned. The endosomal sorting complex required for transport (ESCRT) is multisubunit machinery that is involved in various cellular processes when membrane scission is needed. ESCRT subcomplexes regulate dendrite pruning in Drosophila neurons. However, the contribution of ESCRT components to the dendritogenesis of mammalian neurons and control of dendrite stability remains poorly defined. In the present study, we found that ESCRT-0, ESCRT-I, ESCRT-II, and ESCRT-III and Vps4 are required for proper dendrite morphology under basal culture conditions and for accelerated dendritogenesis in response to phosphoinositide 3-kinase (PI3K) activation. The knockdown of Vps28 (ESCRT-I) and Vps25 (ESCRT-II) resulted in downregulation of the activity of mechanistic/mammalian target of rapamycin complex 1. We also demonstrated that Vps28, Vps24, and Vps25 are required for dendrite stabilization in mature neurons.

Adaptor Complex 2 Controls Dendrite Morphology via mTOR-Dependent Expression of GluA2

The formation of dendritic arbors in neurons is a highly regulated process. Among the regulators of dendritogenesis are numerous membrane proteins that are eventually internalized via clathrin-mediated endocytosis. AP2 is an adaptor complex that is responsible for recruiting endocytic machinery to internalized cargo. Its direct involvement in dendritogenesis in mammalian neurons has not yet been tested. We found that the knockdown of AP2b1 (β2-adaptin), an AP2 subunit, reduced the number of dendrites in developing rat hippocampal neurons and decreased α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluA2 levels by inhibiting mechanistic/mammalian target of rapamycin (mTOR). The dendritic tree abruption that was caused by AP2b1 knockdown was rescued by the overexpression of GluA2 or restoration of the activity of the mTOR effector p70S6 kinase (S6K1). Altogether, this work provides evidence that the AP2 adaptor complex is needed for the dendritogenesis of mammalian neurons and reveals that mTOR-dependent GluA2 biosynthesis contributes to this process.

CD44 regulates dendrite morphogenesis through Src tyrosine kinase-dependent positioning of the Golgi

The acquisition of proper dendrite morphology is a crucial aspect of neuronal development towards the formation of a functional network. The role of the extracellular matrix and its cellular receptors in this process has remained enigmatic. We report that the CD44 adhesion molecule, the main hyaluronan receptor, is localized in dendrites and plays a crucial inhibitory role in dendritic tree arborization in vitro and in vivo. This novel function is exerted by the activation of Src tyrosine kinase, leading to the alteration of Golgi morphology. The mechanism operates during normal brain development, but its inhibition might have a protective influence on dendritic trees under toxic conditions, during which the silencing of CD44 expression prevents dendritic shortening induced by glutamate exposure. Overall, our results indicate a novel role for CD44 as an essential regulator of dendritic arbor complexity in both health and disease.

Cyr61, a matricellular protein, is needed for dendritic arborization of hippocampal neurons

The shape of the dendritic arbor is one of the criteria of neuron classification and reflects functional specialization of particular classes of neurons. The development of a proper dendritic branching pattern strongly relies on interactions between the extracellular environment and intracellular processes responsible for dendrite growth and stability. We previously showed that mammalian target of rapamycin (mTOR) kinase is crucial for this process. In this work, we performed a screen for modifiers of dendritic growth in hippocampal neurons, the expression of which is potentially regulated by mTOR. As a result, we identified Cyr61, an angiogenic factor with unknown neuronal function, as a novel regulator of dendritic growth, which controls dendritic growth in a β1-integrin-dependent manner.

Mammalian target of rapamycin complex 1 (mTORC1) and 2 (mTORC2) control the dendritic arbor morphology of hippocampal neurons

Dendrites are the main site of information input into neurons. Their development is a multistep process controlled by mammalian target of rapamycin (mTOR) among other proteins. mTOR is a serine/threonine protein kinase that forms two functionally distinct complexes in mammalian cells: mTORC1 and mTORC2. However, the one that contributes to mammalian neuron development remains unknown. This work used short hairpin RNA against Raptor and Rictor, unique components of mTORC1 and mTORC2, respectively, to dissect mTORC involvement in this process. We provide evidence that both mTOR complexes are crucial for the proper dendritic arbor morphology of hippocampal neurons. These two complexes are required for dendritic development both under basal conditions and upon the induction of mTOR-dependent dendritic growth. We also identified Akt as a downstream effector of mTORC2 needed for proper dendritic arbor morphology, the action of which required mTORC1 and p70S6K1.

CLIP-170 and IQGAP1 cooperatively regulate dendrite morphology

Dendritic arbors are compartments of neurons dedicated to receiving synaptic inputs. Their shape is an outcome of both the intrinsic genetic program and environmental signals. The microtubules and actin cytoskeleton are both crucial for proper dendritic morphology, but how they interact is unclear. The present study demonstrates that microtubule plus-end tracking protein CLIP-170 and actin-binding protein IQGAP1 regulate dendrite morphology of rat neurons by coordinating the interaction between microtubules and the actin cytoskeleton. Moreover, we show that mTOR kinase interacts with CLIP-170 and is needed for efficient formation of a protein complex containing CLIP-170 and IQGAP1. Dynamic microtubules, CLIP-170, and IQGAP1 are required for proper dendritic arbor morphology and PI3K-mTOR-induced increase in dendritic arbor complexity. Moreover, CLIP-170 and IQGAP1 knockdown modulates dendritic arbor growth via regulation of the actin cytoskeleton. We postulate that mTOR controls dendritic arbor morphology by enhancing cross talk between dynamic microtubules and actin through CLIP-170 and IQGAP1.

Viral vector approaches to modify gene expression in the brain

The use of viral vectors as gene transfer tools for the central nervous system has seen a significant growth in the last decade. Improvements in the safety, efficiency and specificity of vectors for clinical applications have proven to be beneficial also for basic neuroscience research. This review will discuss the viral systems currently available to neuroscientists and some of the recent achievements in the study of synaptic function, memory and drug addiction.

Effect of inducible expressed human cytomegalovirus immediate early 86 protein on cell apoptosis

Human cytomegalovirus is a common human pathogen that can cause life-threatening disease under certain conditions. During infection of host cells, the virus expresses regulatory proteins such as IE72 and IE86 that are important for viral propagation. IE86 plays a critical role in the modulation of viral replication as well as host cell cycle control and apoptosis. In this study, a Tet-On system was used to quantify the effect of IE86 on apoptosis and p53 expression. Our results indicate that IE86 inhibits tumor necrosis factor (TNF)-alpha induced apoptosis and that the anti-apoptotic activity of this viral protein correlates with its expression levels. In addition, IE86 did not alter the mRNA level of p53. The system developed should provide a method for functional analysis of human cytomegalovirus (HCMV) IE86 protein.

Human adipose tissue stromal vascular fraction cells differentiate depending on distinct types of media

OBJECTIVES

Angiogenesis, the process of formation of blood vessels, is essential for many physiological as well as pathological processes. It has been shown that human adipose tissue contains a population of non-characterized cells, called stromal-vascular fraction (SVF) cells, which are able to differentiate into several lineages. The aim of this study was to determine conditions for promoting differentiation of human adipose tissue progenitors towards endothelial cells, as well as to show that SVF cells cooperate with differentiated endothelium in capillary network formation.

MATERIALS AND METHODS

Stromal vascular fraction cells were isolated according to modified Hauner's method and after adaptation they were cultured in pro-angiogenic or pro-adipogenic medium. Cells were characterized by presence of surface antigens by flow cytometry, and by expression of genes characteristic for endothelial cells or for adipocytes, quantitative real-time polymerase chain reaction. A number of tests were performed to verify their differentiation.

RESULTS

Differentiation of human SVF cells towards endothelium was stimulated by the presence of serum and absence of adipogenic factors, documented by the pattern of gene expression as well as different functional in vitro assays. SVF cells were found to work together with human umbilical vein endothelial cells to form capillary networks.

CONCLUSIONS

Here, we show that differentiation of SVF cells to endothelial cells or adipocyte-like cells depended on the medium used. Our work provides a clear model for analysing the differentiation capacity of SVF cells.

Inducibility of doxycycline-regulated gene in neural and neuroendocrine cells strongly depends on the appropriate choice of a tetracycline-responsive promoter

Elucidation of the mechanisms underlying specific receptor activation of neural and neuroendocrine cells will require the establishment of cellular systems that permit the regulation of the expression of the protein of interest. In a tetracycline (Tet)-regulated system, the gene encoding the protein of interest is under the control of a Tet promoter and its transcription is activated in the presence of doxycycline (Dox) by the Tet transactivator rtTA. Acceptable inducibility of the gene's expression requires a high level of its expression in the presence of Dox and a minimal basal expression in the absence of Dox. Two Tet promoters are compared here, the original PhCMV*-1 and the second-generation Ptight, with respect to the inducibility of the gene of interest in neuroendocrine and neural cells genetically engineered to express rtTA, namely PC12-Tet-On cells and MB-G-18 cells (mouse brain-derived cells with the phenotype of neuron-restricted precursors). This study demonstrates that the use of Ptight provided a much higher Dox-induced maximal expression in both cell lines, while the basal activities of the two Tet promoters were at similar levels. The additional use of the Tet-controlled silencer (tTS) caused almost complete abrogation of the leakiness of the Ptight promoter and an increase in the inducibility of the regulated gene, but the maximal levels of gene expression driven in the presence of Dox were also markedly reduced.

Conditional transgenesis and recombination to study the molecular mechanisms of brain plasticity and memory

In the postgenomic era, a primary focus of mouse genetics is to elucidate the role of individual genes in vivo. However, in the nervous system, studying the contribution of specific genes to brain functions is difficult because the brain is a highly complex organ with multiple neuroanatomical structures, orchestrating virtually every function in the body. Further, higher-order brain functions such as learning and memory simultaneously recruit several signaling cascades in different subcellular compartments and have highly fine-tuned spatial and temporal components. Conditional transgenic and gene targeting methodologies, however, now offer valuable tools with improved spatial and temporal resolution for appropriate studies of these functions. This chapter provides an overview of these tools and describes how they have helped gain better understanding of the role of candidate genes such as the NMDA receptor, the protein kinase CaMKIIIalpha, the protein phosphatases calcineurin and PP1, or the transcription factor CREB, in the processes of learning and memory. This review illustrates the broad and innovative applicability of these methodologies to the study of brain plasticity and cognitive functions.