Yasuhiko Kanou

Spatiotemporal expression of BDNF in the hippocampus induced by the continuous intracerebroventricular infusion of β-amyloid in rats

The beta-amyloid protein (Abeta) is the major component of senile plaques found in the brain in Alzheimers disease (AD). Its neurotoxic properties in vivo, however, are not well defined. Since the expression of neurotrophin genes is considered an important component of the intrinsic neuroprotective response to insults, we analyzed the gene expression of neurotrophins in the brains of rats which received a continuous infusion of Abeta-(1-42) into the cerebroventricle. Northern blot analysis revealed a significant increase in brain-derived neurotrophic factor (BDNF) expression in the hippocampus but no change in the cerebral cortices. The alteration peaked on days 3-7 and returned to the basal level on day 14 after the start of Abeta-(1-42) infusion. No significant changes in nerve growth factor or neurotrophin-3 mRNA expression were observed. The infusion of Abeta-(1-40) and (25-35) also triggered the expression of BDNF mRNA, whereas neither Abeta-(40-1) nor (1-16) had any effect. In situ hybridization histochemistry revealed that the expression mainly occurred in the hilus and granular layer of the dentate gyrus and to a lesser extent in the pyramidal neurons of the CA1 region. These results demonstrate that the continuous intracerebroventricular infusion of Abeta induces selective and spatiotemporal expression of BDNF mRNA in the hippocampus.

A novel Caspr mutation causes the shambling mouse phenotype by disrupting axoglial interactions of myelinated nerves.

The neurological mouse mutation shambling (shm) exhibits ataxia and hindlimb paresis. Positional cloning of shm showed that it encodes contactin-associated protein (Caspr), which is required for formation of the paranodal junction in myelinated nerves. The shm mutation is a TT insertion in the Caspr gene that results in a frame shift and a premature stop codon at the COOH-terminus. The truncated Caspr protein that is generated lacks the transmembrane and cytoplasmic domains. Here, we found that the nodal/paranodal axoplasm of shm mice lack paranodal junctions and contain large mitochondria and abnormal accumulations of cytoplasmic organelles that indicate altered axonal transport. Immunohistochemical analysis of mutant mice showed reduced expression of Caspr, contactin, and neurofascin 155, which are thought to form a protein complex in the paranodal region; protein 4.1B, however, was normally distributed. The mutant mice had aberrant localization of voltage-gated ion channels on the axolemma of nodal/paranodal regions. Electrophysiological analysis demonstrated that the velocityof saltatory conduction was reduced in sciatic nerves and that thevisual response was attenuated in the primary visual cortex. These abnormalities likely contribute to the neurological phenotype of the mutant mice.

Identification of a novel myosin-Va mutation in an ataxic mutant rat, dilute-opisthotonus

Abstract. Mutations of the myosin-Va gene (Myo5a) cause diluted coat color in mice and are occasionally associated with severe neurological disorders. Dilute-opisthotonus (dop) is a spontaneous gene mutation in the rat, and phenotypes of the homozygote (dop/dop) are similar to those of the Myo5a-deficient mouse, suggesting that the mutation resides in the rat Myo5a gene. To elucidate the molecular basis of the dop mutation, we cloned the rat Myo5a cDNA from the wild type and the dop/dop. The wild-type rat Myo5a cDNA contained a 5487-bp ORF and showed higher homology with Myo5a of the other species than Myr6 (Myo5b) in the rat. A 141-bp in-frame deletion was detected in the head region in the dop cDNA. An intragenic rearrangement consisting of a 306-bp inversion associated with 17-bp and 217-bp deletions were identified in the Myo5a gene of the dop genome. This rearrangement involved a 141-bp exon, which was skipped in the dop transcript. The MyoVA protein expression was severely impaired in the dop/dop brain. This is the first report to define the dop mutation as the Myo5a gene abnormality in the rat.

Influence of dietary iodine deficiency on the thyroid gland in Slc26a4-null mutant mice

BackgroundPendred syndrome (PDS) is an autosomal recessive disorder characterized by sensorineural hearing impairment and variable degree of goitrous enlargement of the thyroid gland with a partial defect in iodine organification. The thyroid function phenotype can range from normal function to overt hypothyroidism. It is caused by loss-of-function mutations in the SLC26A4 (PDS) gene. The severity of the goiter has been postulated to depend on the amount of dietary iodine intake. However, direct evidence has not been shown to support this hypothesis. Because Slc26a4-null mice have deafness but do not develop goiter, we fed the mutant mice a control diet or an iodine-deficient diet to evaluate whether iodine deficiency is a causative environmental factor for goiter development in PDS.MethodsWe evaluated the thyroid volume in histological sections with the use of three-dimensional reconstitution software, we measured serum levels of total tri-iodothyronine (TT3) and total thyroxine (TT4) levels, and we studied the thyroid gland morphology by transmission electron microscopy.ResultsTT4 levels became low but TT3 levels did not change significantly after eight weeks of an iodine-deficient diet compared to levels in the control diet animals. Even in Slc26a4-null mice fed an iodine-deficient diet, the volume of the thyroid gland did not increase although the size of each epithelial cell increased with a concomitant decrease of thyroid colloidal area.ConclusionsAn iodine-deficient diet did not induce goiter in Slc26a4-null mice, suggesting that other environmental, epigenetic or genetic factors are involved in goiter development in PDS.

Α-Lipoic acid reduces congenital malformations in the offspring of diabetic mice

The mechanism of diabetes‐induced congenital malformation remains to be elucidated. It has been reported that α‐lipoic acid (LA) prevents neural tube defects (NTDs) in offsprings of rats with streptozotocin‐induced diabetes. Here, we evaluate the protective effect of LA against diabetic embryopathy, including NTDs, cardiovascular malformations (CVMs), and skeletal malformations, in mice.

Inactivation of the Rcan2 Gene in Mice Ameliorates the Age- and Diet-Induced Obesity by Causing a Reduction in Food Intake

Obesity is a serious international health problem that increases the risk of several diet-related chronic diseases. The genetic factors predisposing to obesity are little understood. Rcan2 was originally identified as a thyroid hormone-responsive gene. In the mouse, two splicing variants that harbor distinct tissue-specific expression patterns have been identified: Rcan2-3 is expressed predominately in the brain, whereas Rcan2-1 is expressed in the brain and other tissues such as the heart and skeletal muscle. Here, we show that Rcan2 plays an important role in the development of age- and diet-induced obesity. We found that although the loss of Rcan2 function in mice slowed growth in the first few weeks after birth, it also significantly ameliorated age- and diet-induced obesity in the mice by causing a reduction in food intake rather than increased energy expenditure. Rcan2 expression was most prominent in the ventromedial, dorsomedial and paraventricular hypothalamic nuclei governing energy balance. Fasting and refeeding experiment showed that only Rcan2-3 mRNA expression is up-regulated in the hypothalamus by fasting, and loss of Rcan2 significantly attenuates the hyperphagic response to starvation. Using double-mutant (Lepob/ob Rcan2 −/−) mice, we were also able to demonstrate that Rcan2 and leptin regulate body weight through different pathways. Our findings indicate that there may be an Rcan2-dependent mechanism which regulates food intake and promotes weight gain through a leptin-independent pathway. This study provides novel information on the control of body weight in mice and should improve our understanding of the mechanisms of obesity in humans.