Partial Rescue of Ocular Pigment Cells and Structure by Inducible Ectopic Expression of Mitf-M in MITF-Deficient Mice

Abstract

PurposeComplete deficiency of microphthalmia transcription factor (MITF) in Mitfmi-vga9/mi-vga9 mice is associated with microphthalmia, retinal dysplasia, and albinism. We investigated the ability of dopachrome tautomerase (DCT) promoter-mediated inducible ectopic expression of Mitf-M to rescue these phenotypic abnormalities.MethodsA new mouse line was created with doxycycline-inducible ectopic Mitf-M expression on an Mitf-deficient Mitfmi-vga9 background (DMV mouse). Adult DMV mice were phenotypically characterized and tissues were collected for histology, immunohistochemistry, and evaluation of Mitf, pigmentary genes, and retinal pigment epithelium (RPE) gene expression.ResultsEctopic Mitf-M expression was specifically induced in the eyes, but was not detected in the skin of DMV mice. Inducible expression of Mitf-M partially rescued the microphthalmia, RPE structure, and pigmentation as well as a subset of the choroidal and iris melanocytes but not cutaneous melanocytes. RPE function and vision were not restored in the DMV mice.ConclusionsEctopic expression of Mitf-M during development of Mitf-deficient mice is capable of partially rescuing ocular and retinal structures and uveal melanocytes. These findings provide novel information about the roles of Mitf isoforms in the development of mouse eyes.

Transcript Profiles of Stria Vascularis in Models of Waardenburg Syndrome

“…This study reviewed the changes of Mitf-M mutation on gene expression in the cochlea. Mitf has many subtypes [38], in which type M is specifically expressed in melanocytes [39], by direct association with related pigmentases such as tyrosinase (Tyr), dopachrome tautomerase (Dct), endothelin receptor type B (Ednrb), and solute carrier family 45 member 2 (Slc45a2), regulating the survival, migration, and differentiation of melanocytes [40]. Among them, Mitf-M gene [38,39] plays a key role in regulating tyrosine metabolic pathway and melanin production, mainly regulating downstream pigment-related enzymes such as Tyr, Dct, and Tyrp1.…”

Delineating the role of MITF isoforms in pigmentation and tissue homeostasis

“…In this study, we have generated a specific Mitf‐M knockout mouse and demonstrated that the loss of MITF‐M results in the loss of iris stromal and choroidal melanocytes. Our findings also demonstrate that while Mitf‐M may be expressed in the adult RPE (Maruotti, Thein, Zack, & Esumi, ) and can rescue the loss of pigmentation in Mitf vga9 mice (Michael et al, ), it is not required for pigmentation of the RPE. Additionally, the loss of Mitf‐M increased the size of the kidneys (Figure ), indicating that the loss of a single isoform affects distinct tissues differently, further highlighting the utility of the isoform‐specific knockout reagents generated in this study.…”

“…(b) examination of the expression pattern of isoforms in target tissues of wild-type and Mitf mutant animals to infer their function during development (Bharti et al, 2008); (c) isoform-specific overexpression studies to determine the function of individual isoforms (Michael et al, 2018); or (d) isoform-specific knockouts as previously performed (Bharti et al, 2012;Phelep et al, 2017).…”

“…Although mice with mutations in the promoter regions of Mitf have been identified (Steingrímsson, Copeland, & Jenkins, ), the mutant alleles involve the loss of multiple isoforms, so it is still unclear how specific isoforms of MITF regulate pigmentation. Established methods for studying the role of Mitf isoforms rely on (a) mutant alleles that affect multiple isoforms (Steingrímsson et al, ); (b) examination of the expression pattern of isoforms in target tissues of wild‐type and Mitf mutant animals to infer their function during development (Bharti et al, ); (c) isoform‐specific overexpression studies to determine the function of individual isoforms (Michael et al, ); or (d) isoform‐specific knockouts as previously performed (Bharti et al, ; Phelep et al, ). More precise knockout models are needed to deconvolute the role of individual isoforms in tissue development and disease.…”