The amyloid beta-protein (Abeta) ending at 42 plays a pivotal role in Alzheimer's disease (AD). We have reported previously that intracellular Abeta42 is associated with neuronal apoptosis in vitro and in vivo. Here, we show that intracellular Abeta42 directly activated the p53 promoter, resulting in p53-dependent apoptosis, and that intracellular Abeta40 had a similar but lesser effect. Moreover, oxidative DNA damage induced nuclear localization of Abeta42 with p53 mRNA elevation in guinea-pig primary neurons. Also, p53 expression was elevated in brain of sporadic AD and transgenic mice carrying mutant familial AD genes. Remarkably, accumulation of both Abeta42 and p53 was found in some degenerating-shape neurons in both transgenic mice and human AD cases. Thus, the intracellular Abeta42/p53 pathway may be directly relevant to neuronal loss in AD. Although neurotoxicity of extracellular Abeta is well known and synaptic/mitochondrial dysfunction by intracellular Abeta42 has recently been suggested, intracellular Abeta42 may cause p53-dependent neuronal apoptosis through activation of the p53 promoter; thus demonstrating an alternative pathogenesis in AD.

α-Synuclein is a major constituent of pathological intracellular inclusion bodies, a common feature of several neurodegenerative diseases. Two missense mutations in the α-synuclein gene have been identified in confirmed autosomal-dominant familial Parkinson's disease, which segregate with the illness. However, the physiological function of α-synuclein remains unknown. After biochemical investigations we have revealed tubulin to be an α-synuclein associated/binding protein. Here, we show that α-synuclein induces polymerization of purified tubulin into microtubules. Mutant forms of α-synuclein lose this potential. The binding site of α-synuclein to tubulin is identified, and co-localization of α-synuclein with microtubules is shown in cultured cells. To our knowledge, this is the first demonstration of microtubule-polymerizing activity of α-synuclein. Now we can see a striking resemblance between α-synuclein and tau: both have the same physiological function and pathological features, making abnormal structures in diseased brains known as synucleinopathies and tauopathies. The discovery of a physiological role for α-synuclein may provide a new dimension in researches into the mechanisms of α-synuclein-associated neurodegenerative diseases.

Increasing evidence suggests that ␣-synuclein is a common pathogenic molecule in several neurodegenerative diseases, particularly in Parkinson's disease. To understand ␣-synuclein pathology, we investigated molecules that interact with ␣-synuclein in human and rat brains and identified tubulin as an ␣-synuclein binding-/associated protein. Tubulin co-localized with ␣-synuclein in Lewy bodies and other ␣-synuclein-positive pathological structures. Tubulin initiated and promoted ␣-synuclein fibril formation under physiological conditions in vitro. These findings suggest that an interaction between tubulin and ␣-synuclein might accelerate ␣-synuclein aggregation in diseased brains, leading to the formation of Lewy bodies. The non-␤-amyloid (A␤)1 component of Alzheimer's disease amyloid, or NAC, originally detected in an amyloid-enriched fraction, was shown to be a fragment of its precursor, NACP, by cloning of the full-length cDNA (1). Later, NACP turned out to be a human homologue of Torpedo synuclein (2). Therefore, it is also referred to as human ␣-synuclein (3). ␣-Synuclein is abundant in presynaptic terminals of neurons (4). Recently, two missense mutations in the ␣-synuclein gene (5) were discovered in certain pedigrees with familial Parkinson's disease and were shown to segregate with the illness (6, 7). Shortly thereafter, ␣-synuclein was identified as the major filamentous component of Lewy bodies (LBs) in Parkinson's disease (8, 9) and of cytoplasmic inclusions in multiple system atrophy (MSA) (10 -12).Thus, ␣-synuclein appears to be a common pathogenic molecule in these diseases.Although the physiological role of ␣-synuclein is unknown, ␣-synuclein has the property of forming fibrils by itself in vitro, and mutations of ␣-synuclein accelerate the fibril formation (13,14). However, the vast majority of cases of neurodegenerative diseases associated with LBs or with ␣-synuclein pathology, such as Parkinson's disease, dementia with Lewy bodies (DLB), MSA, and the LB variant of Alzheimer's disease, are sporadic, where wild-type ␣-synuclein has shown to be abnormally accumulated as fibrillar structures. It is therefore likely that at some stage(s) in the fibril formation of ␣-synuclein, either the nucleation and/or the elongation steps should be somehow accelerated in diseased brains, or alternatively, some degradation process(es) of abnormal structures of ␣-synuclein might be defective in those patients (15).With respect to the amyloidogenesis of Alzheimer's disease, it was demonstrated in vitro that a seed of NAC can accelerate A␤ fibril formation, and conversely, a seed of A␤ can promote NAC fibril formation (16). Similarly, heterogeneous molecules could also be involved in the formation of ␣-synuclein fibrils, leading to pathological structures of ␣-synuclein such as LBs.In this study, we performed a biochemical investigation of molecules that interact with ␣-synuclein in the human brain, and we identified tubulin as one of the ␣-synuclein binding/ associated proteins. This interaction was confirmed by co...

The pars tuberalis of the pituitary gland is the regulatory hub for seasonal reproduction in birds and mammals. Although fish also exhibit robust seasonal responses, they do not possess an anatomically distinct pars tuberalis. Here we report that the saccus vasculosus of fish is a seasonal sensor. We observe expression of key genes regulating seasonal reproduction and rhodopsin family genes in the saccus vasculosus of masu salmon. Immunohistochemical studies demonstrate that all of these genes are expressed in the coronet cells of the saccus vasculosus, suggesting the existence of a photoperiodic signalling pathway from light input to neuroendocrine output. In addition, isolated saccus vasculosus has the capacity to respond to photoperiodic signals, and its removal abolishes photoperiodic response of the gonad. Although the physiological role of the saccus vasculosus has been a mystery for several centuries, our findings indicate that the saccus vasculosus acts as a sensor of seasonal changes in day length in fish.