15q13.3 microdeletion syndrome is a genetic disorder caused by a deletion of a region containing seven genes on chromosome 15, MTMR10, FAN1, TRPM1, MIR211, KLF13, OTUD7A, and CHRNA7, and characterized by a wide spectrum of psychiatric disorders. The contribution of each gene in this syndrome has been studied using mutant mouse models, but the phenotypes of these mice do not account for human phenotypes and the results are still controversial. The behavior of Trpm1−/− mice with relation to 15q13.3 microdeletion syndrome has not been investigated due to the visual impairment in these mice, which may confound the results of behavior tests that involve vision. We have now applied a comprehensive behavioral test battery to examine the relationship of TRPM1 and 15q13.3 microdeletion syndrome by using Trpm1 null mutant mice. Our data indicate abnormal behavior of Trpm1−/− mice which may explain some phenotypes of 15q13.3 microdeletion syndrome, including reduction of anxiety behavior, abnormality of social interaction, attenuation in fear memory, and hyperactivity, which is the most prominent phenotype of Trpm1 mutant mice. While the ON visual transduction pathway is impared in Trpm1−/− mice, we did not detect compensatory high sensitivities for other sensory modalities. Although Trpm1−/− mice share the same pathway for visual impairment with mGluR6−/− mice, hyperlocomotion activity has not been reported in mGluR6−/− mice. These data suggest that the phenotype of Trpm1−/− mice extends beyond that expected from visual impairment alone. This is the first evidence to associate TRPM1 with impairment of cognitive function similar to that found in the phenotypes of 15q13.3 microdeletion syndrome.

15q13.3 microdeletion syndrome is a genetic disorder caused by a deletion of a region containing seven genes on chromosome 15, MTMR10, FAN1, TRPM1, MIR211, KLF13, OTUD7A, and CHRNA7, and characterized by a wide spectrum of psychiatric disorders. The contribution of each gene in this syndrome has been studied using mutant mouse models, but no single mouse model recapitulates the whole spectrum of human 15q13.3 microdeletion syndrome. The behavior of Trpm1−/− mice with relation to 15q13.3 microdeletion syndrome has not been investigated due to the visual impairment in these mice, which may confound the results of behavioral tests that involve vision. We have now performed a comprehensive behavioral test battery in Trpm1 null mutant mice to demonstrate the role of Trpm1, which is thought to be solely expressed in the retina, in central nervous system and to examine the relationship of TRPM1 and 15q13.3 microdeletion syndrome. Our data indicate abnormal behavior of Trpm1−/− mice which may explain some phenotypes of 15q13.3 microdeletion syndrome, including reduction of anxiety-like behavior, abnormality of social interaction, attenuation in fear memory, and hyperactivity, which is the most prominent phenotype of Trpm1 mutant mice. While the ON visual transduction pathway is impaired in Trpm1−/− mice, we did not detect compensatory high sensitivities for other sensory modalities. Although Trpm1−/− mice share the same pathway for visual impairment with mGluR6-/- mice, hyperlocomotor activity has not been reported in mGluR6-/- mice. These data suggest that the phenotype of Trpm1−/− mice extends beyond that expected from visual impairment alone. This is the first evidence to associate TRPM1 with impairment of cognitive function similar to that found in the phenotypes of 15q13.3 microdeletion syndrome.

Voltage-sensing proteins generally consist of voltage-sensor domains and pore-gate domains, forming the voltage-gated ion channels. However, there are several unconventional voltage-sensor proteins that lack pore-gate domains, conferring them unique voltage-sensing machinery. TMEM266, which is expressed in cerebellum granule cells, is one of the interesting voltage-sensing proteins that has a putative intracellular coiled-coil and a functionally unidentified cytosolic region instead of a pore-gate domain. Here, we approached the molecular function of TMEM266 by performing co-immunoprecipitation experiments. We unexpectedly discovered that TMEM266 proteins natively interact with the novel short form splice variants that only have voltage-sensor domains and putative cytosolic coiled-coil region in cerebellum. The crystal structure of coiled-coil region of TMEM266 suggested that these coiled-coil regions play significant roles in forming homodimers. In vitro expression experiments supported the idea that short form TMEM266 (sTMEM266) or full length TMEM266 (fTMEM266) form homodimers. We also performed proximity labeling mass spectrometry analysis for fTMEM266 and sTMEM266 using Neuro-2A, neuroblastoma cells, and fTMEM266 showed more interacting molecules than sTMEM266, suggesting that the C-terminal cytosolic region in fTMEM266 binds to various targets. Finally, TMEM266-deficient animals showed the moderate abnormality in open-field test. The present study provides clues about the novel voltage-sensing mechanism mediated by TMEM266.