The gracile axonal dystrophy (gad) mouse is an autosomal recessive mutant that shows sensory ataxia at an early stage, followed by motor ataxia at a later stage. Pathologically, the mutant is characterized by 'dying-back' type axonal degeneration and formation of spheroid bodies in nerve terminals. Recent pathological observations have associated brain ageing and neurodegenerative diseases with progressive accumulation of ubiquitinated protein conjugates. In gad mice, accumulation of amyloid beta-protein and ubiquitin-positive deposits occur retrogradely along the sensory and motor nervous systems. We previously reported that the gad mutation was transmitted by a gene on chromosome 5 (refs 10,11). Here we find that the gad mutation is caused by an in-frame deletion including exons 7 and 8 of Uchl1, encoding the ubiquitin carboxy-terminal hydrolase (UCH) isozyme (Uch-l1) selectively expressed in the nervous system and testis. The gad allele encodes a truncated Uch-l1 lacking a segment of 42 amino acids containing a catalytic residue. As Uch-l1 is thought to stimulate protein degradation by generating free monomeric ubiquitin, the gad mutation appears to affect protein turnover. Our data suggest that altered function of the ubiquitin system directly causes neurodegeneration. The gad mouse provides a useful model for investigating human neurodegenerative disorders.

A recently described form of synaptic plasticity results in dynamic changes in the calcium permeability of synaptic AMPA receptors. Since the AMPA receptor GluR2 subunit confers calcium permeability, this plasticity is thought to occur through the dynamic exchange of synaptic GluR2-lacking and GluR2-containing receptors. To investigate the molecular mechanisms underlying this calcium-permeable AMPA receptor plasticity (CARP), we examined whether AMPA receptor exchange was mediated by subunit-specific protein-protein interactions. We found that two GluR2-interacting proteins, the PDZ domain-containing Protein interacting with C kinase (PICK1) and N-ethylmaleimide sensitive fusion protein (NSF), are specifically required for CARP. Furthermore, PICK1, but not NSF, regulates the formation of extrasynaptic plasma membrane pools of GluR2-containing receptors that may be laterally mobilized into synapses during CARP. These results demonstrate that PICK1 and NSF dynamically regulate the synaptic delivery of GluR2-containing receptors during CARP and thus regulate the calcium permeability of AMPA receptors at excitatory synapses.

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Components of silk including silk fibroin have long been used as anti-diabetic remedies in oriental medicine. However, detailed mechanisms underlying these anti-diabetic effects remain unclear. In this study, we examined the anti-diabetic activity of silk fibroin hydrolysate (SFH) in C57BL/KsJ-db/db (db/db) mice, a well-known animal model of non-insulin dependent diabetes mellitus. When the db/db mice were administered SFH in drinking water for 6 weeks, hyperglycemia in the animals gradually disappeared and the level of glycosylated hemoglobin decreased, indicating that SFH plays important role in reducing the symptoms of diabetes. In addition, SFH-treated db/db mice exhibited improved glucose tolerance with increased plasma insulin levels. Immunohistochemical and morphological analyses showed that SFH up-regulated insulin production by increasing pancreatic β cell mass in the mice. In summary, our results suggest that SFH exerts anti-diabetic effects by increasing pancreatic β cell mass in a non-insulin dependent diabetes mellitus mouse model.

a b s t r a c tTo examine the function of SIRT1 in neuronal differentiation, we employed all-trans retinoic acid (ATRA)-induced differentiation of neuroblastoma cells. Nicotinamide inhibited neurite outgrowth and tyrosine hydroxylase (TH) expression. Inhibition of PARP or histone deacetylase did not inhibit TH expression, showing the effect to be SIRT1 specific. Expression of FOXO3a and its target proteins were increased during the differentiation and reduced by nicotinamide. FOXO3a deacetylation was increased by ATRA and blocked by nicotinamide. SIRT1 and FOXO3a siRNA inhibited ATRA-induced up-regulation of TH and differentiation. Taken together, these results indicate that SIRT1 is involved in ATRA-induced differentiation of neuroblastoma cells via FOXO3a.

Periventricular leukomalacia, specifically characterized as white matter injury, in neonates is strongly associated with the damage of pre-myelinating oligodendrocytes. Clinical data suggest that hypoxia-ischemia during delivery and intrauterine or neonatal infection-inflammation are important factors in the etiology of periventricular leukomalacia including cerebral palsy, a serious case exhibiting neurobehavioral deficits of periventricular leukomalacia. In order to explore the pathophysiological mechanisms of white matter injury and to better understand how infectious agents may affect the vulnerability of the immature brain to injury, novel animal models have been developed using hypoperfusion, microbes or bacterial products (lipopolysaccharide) and excitotoxins. Such efforts have developed rat models that produce predominantly white matter lesions by adopting combined hypoxia-ischemia technique on postnatal days 1-7, in which unilateral or bilateral carotid arteries of animals are occluded (ischemia) followed by 1-2 hour exposure to 6-8% oxygen environment (hypoxia). Furthermore, low doses of lipopolysaccharide that by themselves have no adverse-effects in 7-day-old rats, dramatically increase brain injury to hypoxic-ischemic challenge, implying that inflammation sensitizes the immature central nervous system. Therefore, among numerous models of periventricular leukomalacia, combination of hypoxia-ischemia-lipopolysaccharide might be one of the most-acceptable rodent models to induce extensive white matter injury and ensuing neurobehavioral deficits for the evaluation of candidate therapeutics.

The anatomic and functional combinations of cusps and lophs (ridges) define the tooth shape of rodent molars, which distinguishes species. The species-specific cusp patterns result from the spatiotemporal induction of enamel knots (EKs), which require precisely controlled cellular behavior to control the epithelial invagination. Despite the well-defined roles of EK in cusp patterning, the determinants of the ultimate cuspal shapes and involvement of epithelial cellular geometry are unknown. Using two typical tooth patterns, the lophodont in gerbils and the bunodont in mice, we showed that the cuspal shape is determined by the dental epithelium at the cap stage, whereas the cellular geometry in the inner dental epithelium (IDE) is correlated with the cuspal shape. Intriguingly, fine tuning Rac1 and RhoA interconvert cuspal shapes between two species by remolding the cellular geometry. Either inhibition of Rac1 or ectopic expression of RhoA could region-distinctively change the columnar shape of IDE cells in gerbils to drive invagination to produce cusps. Conversely, RhoA reduction in mice inhibited invagination and developed lophs. Furthermore, we found that Rac1 and RhoA modulate the choices of cuspal shape by coordinating adhesion junctions, actin distribution, and fibronectin localization to drive IDE invagination.

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