Regulation of Neuronal Survival and Axon Growth by a Perinuclear cAMP Compartment.

cAMP signaling is known to be critical in neuronal survival and axon growth. Increasingly the subcellular compartmentation of cAMP signaling has been appreciated, but outside of dendritic synaptic regulation, few cAMP compartments have been defined in terms of molecular composition or function in neurons. Specificity in cAMP signaling is conferred in large part by A-kinase anchoring proteins (AKAPs) that localize protein kinase A and other signaling enzymes to discrete intracellular compartments.

Tumor Suppressors RB1 and CDKN2a Cooperatively Regulate Cell-Cycle Progression and Differentiation During Cardiomyocyte Development and Repair.

Rationale: Although rare cardiomyogenesis is reported in the adult mammalian heart, whether this results from differentiation or proliferation of cardiomyogenic cells remains controversial. The tumor suppressor genes RB1 (retinoblastoma) and CDKN2a (cyclin-dependent kinase inhibitor 2a) are critical cell-cycle regulators, but their roles in human cardiomyogenesis remains unclear.

Objective: We hypothesized that developmental activation of RB1 and CDKN2a cooperatively cause permanent cell-cycle withdrawal of human cardiac precursors (CPCs) driving terminal differentiation into mature cardiomyocytes, and that dual inactivation of these tumor suppressor genes promotes myocyte cell-cycle reentry.

The LYR factors SDHAF1 and SDHAF3 mediate maturation of the iron-sulfur subunit of succinate dehydrogenase.

Disorders arising from impaired assembly of succinate dehydrogenase (SDH) result in a myriad of pathologies, consistent with its unique role in linking the citric acid cycle and electron transport chain. In spite of this critical function, however, only a few factors are known to be required for SDH assembly and function. We show here that two factors, Sdh6 (SDHAF1) and Sdh7 (SDHAF3), mediate maturation of the FeS cluster SDH subunit (Sdh2/SDHB).

Phospho-dependent ubiquitination and degradation of PAR-1 regulates synaptic morphology and tau-mediated Aβ toxicity in Drosophila.

The conserved kinases PAR-1/MARK are critically involved in processes such as asymmetric cell division, cell polarity and neuronal differentiation. Their deregulation has been implicated in diseases including Alzheimer's disease and cancer. Given the importance of PAR-1/MARK in health and disease, their activities need to be tightly controlled.

Synapses and dendritic spines as pathogenic targets in Alzheimer's disease.

Synapses are sites of cell-cell contacts that transmit electrical or chemical signals in the brain. Dendritic spines are protrusions on dendritic shaft where excitatory synapses are located. Synapses and dendritic spines are dynamic structures whose plasticity is thought to underlie learning and memory.

Parkinson's disease-associated kinase PINK1 regulates Miro protein level and axonal transport of mitochondria.

Mutations in Pten-induced kinase 1 (PINK1) are linked to early-onset familial Parkinson's disease (FPD). PINK1 has previously been implicated in mitochondrial fission/fusion dynamics, quality control, and electron transport chain function. However, it is not clear how these processes are interconnected and whether they are sufficient to explain all aspects of PINK1 pathogenesis.

A critical role for the PAR-1/MARK-tau axis in mediating the toxic effects of Aβ on synapses and dendritic spines.

Alzheimer's disease (AD) is the most common neurodegenerative disease and the leading cause of dementia in the elderly. Accumulating evidence supports soluble amyloid-β (Aβ) oligomers as the leading candidate for the causative agent in AD and synapses as the primary site of Aβ oligomer action. However, the molecular and cellular mechanisms by which Aβ oligomers cause synaptic dysfunction and cognitive impairments remain poorly understood.

The PINK1/Parkin pathway regulates mitochondrial dynamics and function in mammalian hippocampal and dopaminergic neurons.

PTEN-induced putative kinase 1 (PINK1) and Parkin act in a common pathway to regulate mitochondrial dynamics, the involvement of which in the pathogenesis of Parkinson's disease (PD) is increasingly being appreciated. However, how the PINK1/Parkin pathway influences mitochondrial function is not well understood, and the exact role of this pathway in controlling mitochondrial dynamics remains controversial. Here we used mammalian primary neurons to examine the function of the PINK1/Parkin pathway in regulating mitochondrial dynamics and function.

Gephyrin interacts with the glutamate receptor interacting protein 1 isoforms at GABAergic synapses.

We have previously shown that the glutamate receptor interacting protein 1 (GRIP1) splice forms GRIP1a/b and GRIP1c4-7 are present at the GABAergic post-synaptic complex. Nevertheless, the role that these GRIP1 protein isoforms play at the GABAergic post-synaptic complex is not known. We are now showing that GRIP1c4-7 and GRIP1a/b interact with gephyrin, the main post-synaptic scaffold protein of GABAergic and glycinergic synapses.

Gephyrin expression and clustering affects the size of glutamatergic synaptic contacts.

We have recently shown that disrupting the expression and post-synaptic clustering of gephyrin in cultured hippocampal pyramidal cells, by either gephyrin RNAi (RNA interference) or over-expression of a dominant negative gephyrin-enhanced green fluorescent protein (EGFP) fusion protein, leads to decreased number of post-synaptic gephyrin and GABA(A) receptor clusters and to reduced GABAergic innervation of these cells. On the other hand, increasing gephyrin expression led to a small increase in the number of gephyrin and GABA(A) receptor clusters and to little or no effect on GABAergic innervation. We are now reporting that altering gephyrin expression and clustering affects the size but not the density of glutamatergic synaptic contacts.

Disruption of postsynaptic GABA receptor clusters leads to decreased GABAergic innervation of pyramidal neurons.

We have used RNA interference (RNAi) to knock down the expression of the gamma2 subunit of the GABA(A) receptors (GABA(A)Rs) in pyramidal neurons in culture and in the intact brain. Two hairpin small interference RNAs (shRNAs) for the gamma2 subunit, one targeting the coding region and the other one the 3'-untranslated region (UTR) of the gamma2 mRNA, when introduced into cultured rat hippocampal pyramidal neurons, efficiently inhibited the synthesis of the GABA(A) receptor gamma2 subunit and the clustering of other GABA(A)R subunits and gephyrin in these cells. More significantly, this effect was accompanied by a reduction of the GABAergic innervation that these neurons received.

A four PDZ domain-containing splice variant form of GRIP1 is localized in GABAergic and glutamatergic synapses in the brain.

We have isolated, from a rat brain cDNA library, a clone corresponding to a 2779-bp cDNA encoding a novel splice form of the glutamate receptor interacting protein-1 (GRIP1). We call this 696-amino acid splice form GRIP1c 4-7 to differentiate it from longer splice forms of GRIP1a/b containing seven PDZ domains. The four PDZ domains of GRIP1c 4-7 are identical to PDZ domains 4-7 of GRIP1a/b.

The brefeldin A-inhibited GDP/GTP exchange factor 2, a protein involved in vesicular trafficking, interacts with the beta subunits of the GABA receptors.

We have found that the brefeldin A-inhibited GDP/GTP exchange factor 2 (BIG2) interacts with the beta subunits of the gamma-aminobutyric acid type-A receptor (GABA(A)R). BIG2 is a Sec7 domain-containing guanine nucleotide exchange factor known to be involved in vesicular and protein trafficking. The interaction between the 110 amino acid C-terminal fragment of BIG2 and the large intracellular loop of the GABA(A)R beta subunits was revealed with a yeast two-hybrid assay.