Zebrafish trpm7 mutants show reduced motility in free movement.

Parkinson's disease is a neurological disorder characterized by reduced motility, depression and dementia. Guamanian parkinsonism dementia with amyotrophic sclerosis is a local case of Parkinson's disease reported in the Western Pacific Islands of Guam and Rota as well as in the Kii Peninsula of Japan. A previous genetic study has suggested that Guamanian parkinsonism is attributable to a variant of the TRPM7 gene, which encodes for melastatin-related transient receptor potential (TRP) ion channels. But the link between parkinsonism and the TRPM7 gene remains elusive. Previous studies have addressed that trpm7-deficient zebrafish embryos showed defects in pigmentation and touch-evoked motor response. In this study, we identified a new viable allele of trpm7 mutant causing an I756N amino acid substitution in the first transmembrane domain. Behavioral analyses revealed that trpm7 mutants showed compromised motility with their movement distance shorter than wild-type larvae. The velocity of the movement was significantly reduced in trpm7 mutants than in wild-type larvae. Along with a previous finding of reduced dopaminergic neurons in zebrafish trpm7 mutants, reduced motility of trpm7 mutants can suggest another similarity between trpm7 phenotypes and Parkinson's disease symptoms.