Eye specific transcription start site (TSS) of mouse Itpr1

Mutations in ITPR1 cause ataxia and aniridia in individuals with Gillespie syndrome (GLSP). However, the underlying pathogenic mechanism of aniridia remains unclear. We identified a de novo GLSP mutation hotspot in the 3-region of ITPR1 in five individuals with GLSP. Mutations or deletions in the anterior half of ITPR1 result in autosomal-dominant neurological disorders, spinocerebellar ataxia; however, individuals with spinocerebellar do not exhibit aniridia. Therefore, we hypothesized the existence of an undiscovered TSS near the 3-end of ITPR. To confirm this hypothesis, we performed RNA-seq using total RNA extracted from the eyes and brains of generated genetically modified mice harboring a V5-tag in frame at the 3-terminus of Itpr1. RNA-seq and immunoblotting revealed an eye-specific transcript encoding 218 amino acids of Itpr1.