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1.  SLITRK6 mutations cause myopia and deafness in humans and mice  
The Journal of Clinical Investigation  2013;123(5):2094-2102.
Myopia is by far the most common human eye disorder that is known to have a clear, albeit poorly defined, heritable component. In this study, we describe an autosomal-recessive syndrome characterized by high myopia and sensorineural deafness. Our molecular investigation in 3 families led to the identification of 3 homozygous nonsense mutations (p.R181X, p.S297X, and p.Q414X) in SLIT and NTRK-like family, member 6 (SLITRK6), a leucine-rich repeat domain transmembrane protein. All 3 mutant SLITRK6 proteins displayed defective cell surface localization. High-resolution MRI of WT and Slitrk6-deficient mouse eyes revealed axial length increase in the mutant (the endophenotype of myopia). Additionally, mutant mice exhibited auditory function deficits that mirrored the human phenotype. Histological investigation of WT and Slitrk6-deficient mouse retinas in postnatal development indicated a delay in synaptogenesis in Slitrk6-deficient animals. Taken together, our results showed that SLITRK6 plays a crucial role in the development of normal hearing as well as vision in humans and in mice and that its disruption leads to a syndrome characterized by severe myopia and deafness.
PMCID: PMC3635725  PMID: 23543054
2.  Selective control of inhibitory synapse development by Slitrk3-PTPδ trans-synaptic interaction 
Nature neuroscience  2012;15(3):389-S2.
Balanced development of excitatory and inhibitory synapses is required for normal brain function, and their imbalance may underlie pathogenesis of neuropsychiatric disorders. Compared with many identified trans-synaptic adhesion complexes that organize excitatory synapses, little is known about organizers specific for inhibitory synapses. Here we report Slit and NTRK-like family member 3 (Slitrk3) as a postsynaptic adhesion molecule that selectively regulates inhibitory synapse development via trans-interaction with axonal tyrosine phosphatase receptor PTPδ. Slitrk3 expressed in fibroblasts triggers only inhibitory presynaptic differentiation in contacting axons of cocultured rat hippocampal neurons. Recombinant Slitrk3 preferentially localizes to inhibitory postsynaptic sites. Slitrk3-deficient mice exhibit decreases in inhibitory but not excitatory synapse number and function in hippocampal CA1 neurons and exhibit increased seizure susceptibility and spontaneous epileptiform activity. Slitrk3 requires trans-interaction with axonal PTPδ to induce inhibitory presynaptic differentiation. These results identify Slitrk3-PTPδ as an inhibitory-specific trans-synaptic organizing complex required for normal functional GABAergic synapse development.
PMCID: PMC3288805  PMID: 22286174
3.  Sequential irinotecan hydrochloride/S-1 for S-1-resistant inoperable gastric cancer: A feasibility study 
Oncology Letters  2011;3(1):89-93.
Irinotecan hydrochloride (CPT-11) is reported to be involved in the downregulation of thymidylate synthase (TS), a target molecule of 5-fluorouracil (5-FU) and oral fluoropyrimidine S-1. Therefore, we hypothesized that a preceding administration of CPT-11 against S-1-resistant tumors may recover sensitivity to S-1. To this end, we planned a S-1/CPT-11 sequential therapy as a feasibility study in S-1-refractory gastric cancer patients. In the first course, CPT-11 was administered intravenously at 150 mg/m2 on days 1 and 15. Subsequently, S-1 was administered orally for 4 weeks from day 29 to 57, followed by a 2-week interval (sequential S-1/CPT-11). When the tumor showed a complete response (CR) or partial response (PR), the same dose of S-1 monotherapy was continued unless progressive disease (PD) was observed. When the response was stable disease (SD), S-1 was administered at the same dose for just 2 weeks (days 1–15), no drug was administered for the following 2 weeks (4-week cycle) and CPT-11 was administered intravenously at 100 mg/m2 on days 1 and 15 (concurrent S-1/CPT-11) unless PD was observed. In the case of PD, the study was terminated. The primary endpoint was an antitumor effect and secondary endpoints were median survival time (MST), progression-free survival (PFS), time-to-treatment failure (TTF) and safety. The response rate (RR) following the first course was only 5.9% and the most positive RR was 11.8%. The MST, median TTF and PFS were 381, 69 and 71 days, respectively. Leukocytopenia was observed in more than half of the patients. Since the RR was lower than estimated in an interim analysis, the trial was terminated and the protocol was concluded to be unfeasible.
PMCID: PMC3362594  PMID: 22740861
CPT-11; S-1; gastric cancer
4.  Impaired Auditory-Vestibular Functions and Behavioral Abnormalities of Slitrk6-Deficient Mice 
PLoS ONE  2011;6(1):e16497.
A recent study revealed that Slitrk6, a transmembrane protein containing a leucine-rich repeat domain, has a critical role in the development of the inner ear neural circuit. However, it is still unknown how the absence of Slitrk6 affects auditory and vestibular functions. In addition, the role of Slitrk6 in regions of the central nervous system, including the dorsal thalamus, has not been addressed. To understand the physiological role of Slitrk6, Slitrk6-knockout (KO) mice were subjected to systematic behavioral analyses including auditory and vestibular function tests. Compared to wild-type mice, the auditory brainstem response (ABR) of Slitrk6-KO mice indicated a mid-frequency range (8–16 kHz) hearing loss and reduction of the first ABR wave. The auditory startle response was also reduced. A vestibulo-ocular reflex (VOR) test showed decreased vertical (head movement–induced) VOR gains and normal horizontal VOR. In an open field test, locomotor activity was reduced; the tendency to be in the center region was increased, but only in the first 5 min of the test, indicating altered adaptive responses to a novel environment. Altered adaptive responses were also found in a hole-board test in which head-dip behavior was increased and advanced. Aside from these abnormalities, no clear abnormalities were noted in the mood, anxiety, learning, spatial memory, or fear memory–related behavioral tests. These results indicate that the Slitrk6-KO mouse can serve as a model of hereditary sensorineural deafness. Furthermore, the altered responses of Slitrk6-KO mice to the novel environment suggest a role of Slitrk6 in some cognitive functions.
PMCID: PMC3027700  PMID: 21298075
5.  Disorganized Innervation and Neuronal Loss in the Inner Ear of Slitrk6-Deficient Mice 
PLoS ONE  2009;4(11):e7786.
Slitrks are type I transmembrane proteins that share conserved leucine-rich repeat domains similar to those in the secreted axonal guidance molecule Slit. They also show similarities to Ntrk neurotrophin receptors in their carboxy-termini, sharing a conserved tyrosine residue. Among 6 Slitrk family genes in mammals, Slitrk6 has a unique expression pattern, with strong expression in the sensory epithelia of the inner ear. We generated Slitrk6-knockout mice and investigated the development of their auditory and vestibular sensory organs. Slitrk6-deficient mice showed pronounced reduction in the cochlear innervation. In the vestibule, the innervation to the posterior crista was often lost, reduced, or sometimes misguided. These defects were accompanied by the loss of neurons in the spiral and vestibular ganglia. Cochlear sensory epithelia from Slitrk6-knockout mice have reduced ability in promoting neurite outgrowth of spiral ganglion neurons. Indeed the Slitrk6-deficient inner ear showed a mild but significant decrease in the expression of Bdnf and Ntf3, both of which are essential for the innervation and survival of sensory neurons. In addition, the expression of Ntrk receptors, including their phosphorylated forms was decreased in Slitrk6-knockout cochlea. These results suggest that Slitrk6 promotes innervation and survival of inner ear sensory neurons by regulating the expression of trophic and/or tropic factors including neurotrophins from sensory epithelia.
PMCID: PMC2777407  PMID: 19936227
6.  Medaka: a promising model animal for comparative population genomics 
BMC Research Notes  2009;2:88.
Within-species genome diversity has been best studied in humans. The international HapMap project has revealed a tremendous amount of single-nucleotide polymorphisms (SNPs) among humans, many of which show signals of positive selection during human evolution. In most of the cases, however, functional differences between the alleles remain experimentally unverified due to the inherent difficulty of human genetic studies. It would therefore be highly useful to have a vertebrate model with the following characteristics: (1) high within-species genetic diversity, (2) a variety of gene-manipulation protocols already developed, and (3) a completely sequenced genome. Medaka (Oryzias latipes) and its congeneric species, tiny fresh-water teleosts distributed broadly in East and Southeast Asia, meet these criteria.
Using Oryzias species from 27 local populations, we conducted a simple screening of nonsynonymous SNPs for 11 genes with apparent orthology between medaka and humans. We found medaka SNPs for which the same sites in human orthologs are known to be highly differentiated among the HapMap populations. Importantly, some of these SNPs show signals of positive selection.
These results indicate that medaka is a promising model system for comparative population genomics exploring the functional and adaptive significance of allelic differentiations.
PMCID: PMC2683866  PMID: 19426554
7.  Importance of Achromatic Contrast in Short-Range Fruit Foraging of Primates 
PLoS ONE  2008;3(10):e3356.
Trichromatic primates have a ‘red-green’ chromatic channel in addition to luminance and ‘blue-yellow’ channels. It has been argued that the red-green channel evolved in primates as an adaptation for detecting reddish or yellowish objects, such as ripe fruits, against a background of foliage. However, foraging advantages to trichromatic primates remain unverified by behavioral observation of primates in their natural habitats. New World monkeys (platyrrhines) are an excellent model for this evaluation because of the highly polymorphic nature of their color vision due to allelic variation of the L-M opsin gene on the X chromosome. In this study we carried out field observations of a group of wild, frugivorous black-handed spider monkeys (Ateles geoffroyi frontatus, Gray 1842, Platyrrhini), consisting of both dichromats (n = 12) and trichromats (n = 9) in Santa Rosa National Park, Costa Rica. We determined the color vision types of individuals in this group by genotyping their L-M opsin and measured foraging efficiency of each individual for fruits located at a grasping distance. Contrary to the predicted advantage for trichromats, there was no significant difference between dichromats and trichromats in foraging efficiency and we found that the luminance contrast was the main determinant of the variation of foraging efficiency among red-green, blue-yellow and luminance contrasts. Our results suggest that luminance contrast can serve as an important cue in short-range foraging attempts despite other sensory cues that could be available. Additionally, the advantage of red-green color vision in primates may not be as salient as previously thought and needs to be evaluated in further field observations.
PMCID: PMC2559900  PMID: 18836576
8.  Nitric oxide (NO)-dependent and NO-independent signaling pathways act in ABA-inhibition of stomatal opening 
Plant Signaling & Behavior  2008;3(2):131-132.
We investigated the role of nitric oxide (NO) in ABA-inhibition of stomatal opening in Vicia faba L. in different size dishes. When a large dish (9 cm diameter) was used, ABA induced NO synthesis and the NO scavenger reduced ABA-inhibition of stomatal opening. When a small dish (6 cm diameter) was used, ABA induced stomatal closure and inhibited stomatal opening. The NO scavenger was able to reduce ABA-induced stomatal closure, but unable to reverse ABA-inhibition of stomatal opening. Furthermore, NO was not synthesized in response to ABA, indicating that NO is not required for ABA-inhibition of stomatal opening in the small dish. These results indicated that an NO-dependent and an NO-independent signaling pathway participate in ABA signaling pathway. An NO-dependent pathway is the major player in ABA-induced stomatal closure. However, in ABA-inhibition of stomatal opening, an NO-dependent and an NO-independent pathway act: different signaling molecules participate in ABA-signaling cascade under different environmental condition.
PMCID: PMC2634002  PMID: 19704732
ABA; environmental condition; nitric oxide; stomata; Vicia faba L
9.  Evolutionary renovation of L/M opsin polymorphism confers a fruit discrimination advantage to ateline New World monkeys 
Molecular Ecology  2014;23(7):1799-1812.
New World monkeys exhibit prominent colour vision variation due to allelic polymorphism of the long-to-middle wavelength (L/M) opsin gene. The known spectral variation of L/M opsins in primates is broadly determined by amino acid composition at three sites: 180, 277 and 285 (the ‘three-sites’ rule). However, two L/M opsin alleles found in the black-handed spider monkeys (Ateles geoffroyi) are known exceptions, presumably due to novel mutations. The spectral separation of the two L/M photopigments is 1.5 times greater than expected based on the ‘three-sites’ rule. Yet the consequence of this for the visual ecology of the species is unknown, as is the evolutionary mechanism by which spectral shift was achieved. In this study, we first examine L/M opsins of two other Atelinae species, the long-haired spider monkeys (A. belzebuth) and the common woolly monkeys (Lagothrix lagotricha). By a series of site-directed mutagenesis, we show that a mutation Y213D (tyrosine to aspartic acid at site 213) in the ancestral opsin of the two alleles enabled N294K, which occurred in one allele of the ateline ancestor and increased the spectral separation between the two alleles. Second, by modelling the chromaticity of dietary fruits and background leaves in a natural habitat of spider monkeys, we demonstrate that chromatic discrimination of fruit from leaves is significantly enhanced by these mutations. This evolutionary renovation of L/M opsin polymorphism in atelines illustrates a previously unappreciated dynamism of opsin genes in shaping primate colour vision.
PMCID: PMC4260670  PMID: 24612406
spectral differentiation; spider monkeys; visual pigments; woolly monkeys

Results 1-9 (9)