Depolarizing bipolar cell dysfunction due to a Trpm1 point mutation

Abstract

Mutations in TRPM1 are found in humans with an autosomal recessive form of complete congenital stationary night blindness (cCSNB). The Trpm1(-/-) mouse has been an important animal model for this condition. Here we report a new mouse mutant, tvrm27, identified in a chemical mutagenesis screen. Genetic mapping of the no b-wave electroretinogram (ERG) phenotype of tvrm27 localized the mutation to a chromosomal region that included Trpm1. Complementation testing with Trpm1(-/-) mice confirmed a mutation in Trpm1. Sequencing identified a nucleotide change in exon 23, converting a highly conserved alanine within the pore domain to threonine (p.A1068T). Consistent with prior studies of Trpm1(-/-) mice, no anatomical changes were noted in the Trpm1(tvrm27/tvrm27) retina. The Trpm1(tvrm27/tvrm27) phenotype is distinguished from that of Trpm1(-/-) by the retention of TRPM1 expression on the dendritic tips of depolarizing bipolar cells (DBCs). While ERG b-wave amplitudes of Trpm1(+/-) heterozygotes are comparable to wild type, those of Trpm1(+/tvrm27) mice are reduced by 32%. A similar reduction in the response of Trpm1(+/tvrm27) DBCs to LY341495 or capsaicin is evident in whole cell recordings. These data indicate that the p.A1068T mutant TRPM1 acts as a dominant negative with respect to TRPM1 channel function. Furthermore, these data indicate that the number of functional TRPM1 channels at the DBC dendritic tips is a key factor in defining DBC response amplitude. The Trpm1(tvrm27/tvrm27) mutant will be useful for elucidating the role of TRPM1 in DBC signal transduction, for determining how Trpm1 mutations impact central visual processing, and for evaluating experimental therapies for cCSNB.

Synaptic pathology and therapeutic repair in adult retinoschisis mouse by AAV-RS1 transfer

“…The molecular and cellular processes that support ERG b-wave generation in depolarizing bipolar cells (DBCs) have been well characterized. In this pathway, mGluR6 (20,21) regulates the activity of a nonselective cation channel, transient receptor potential melastatin subfamily M member 1 (TRPM1) (22)(23)(24), via a heterotrimeric G O protein subunit Gαo (25). Other accessory proteins include Gβ5, a member of the heterotrimeric G protein β subunit family (26), the regulators of G protein signaling (RGS) RGS7 and RGS11 (27,28), and the scaffolding protein nyctalopin, a product of the NYX gene (29,30).…”

Constructing the rod bipolar cell signalplex using animal models of retinal dysfunction.

“…In other cases, the mutations were in genes already known to cause the nob phenotype but offer unique insights into protein properties that the knockout model does not display Peachey et al, 2012a).…”

Oligomeric State of Purified Transient Receptor Potential Melastatin-1 (TRPM1), a Protein Essential for Dim Light Vision

“…TRPM1 knock-out mice have a no-b-wave (nob) electroretinogram phenotype (17,21) and defective ON bipolar cell signaling in whole-cell recordings (17,22,23). In addition, a nob mouse derived from a mutagenesis screen was found to have a point mutation in the predicted pore region of TRPM1 (24). Genetic lesions in the TRPM1 gene are also associated with complete congenital stationary night blindness in humans (25)(26)(27)(28).…”