Distinct distal regulatory elements control tyrosinase expression in melanocytes and the retinal pigment epithelium

Abstract

Pigment cells of mammals are characterized by two different developmental origins: cells of the retinal pigment epithelium (RPE) originate from the optic cup of the developing forebrain, whereas melanocytes arise from the neural crest. The pigmentation gene tyrosinase is expressed in all pigment cells but differentially regulated in melanocytes and RPE. The tyrosinase promoter does not confer strong expression in pigment cells in vivo, while inclusion of a distal regulatory element at position -15 kb is necessary and sufficient to provide strong expression in melanocytes. Nevertheless, the regulatory elements responsible for correct spatial and temporal tyrosinase expression in the RPE remained unidentified so far. In this report, we show that a 186 kb BAC containing the tyrosinase gene provides transgene expression in both RPE and melanocytes indicating the presence of regulatory sequences required for expression in the RPE. A deletion analysis of the BAC was performed demonstrating that a RPE-regulatory element resides between -17 and -75 kb. Using multi-species comparative genomic analysis we identified three conserved sequences within this region. When tested in transgenic mice one of these sequences located at -47 kb targeted expression to the RPE. In addition, deletion of this regulatory element within a tyrosinase::lacZ BAC provided evidence that this sequence is not only sufficient but also required for correct spatial and temporal expression in the RPE. The identification of this novel element demonstrates that tyrosinase gene expression is controlled by separate distal regulatory sequences in melanocytes and RPE.

RBP-Jκ-dependent Notch signaling enhances retinal pigment epithelial cell proliferation in transgenic mice

“…Notch signaling activity maintains a proliferative state in RPE precursor cells Although melanocytes and RPE cells share distinct regulatory elements controlling the expression of pigment-cell-specific genes (Murisier et al, 2006(Murisier et al, , 2007, both respond similarly to Notch signals. Although Notch activity might increase melanoblast and melanocyte numbers (Schouwey et al, 2010), and is capable to transform melanocytes (Pinnix et al, 2009), sustained Notch signaling activity in Tyrp1::NotchIC/1 RPE results in hyperproliferation and formation of tumors showing pigmented and unpigmented areas.…”

“…In addition to neural crest-derived melanocytes found in skin and hair follicles, as well as in the choroid and the iris of the eye, a minor population of pigment cells originates from the optic cup of the developing forebrain and forms the retinal pigment epithelium (RPE), a cell monolayer lying between the photoreceptive neural retina and the choroid (MartinezMorales et al, 2004). Both pigment cells produce melanin, but have adopted distinct regulatory elements controlling the expression of pigment-cell-specific genes, such as tyrosinase, Tyrp1 and Dct, probably because of an independent evolution of these regulatory networks (Murisier et al, 2006(Murisier et al, , 2007. Moreover, severe mutations of Mitf lead to death of melanocytes, whereas RPE cells survive and hyperproliferate (Bumsted and Barnstable, 2000;Nguyen and Arnheiter, 2000;Bharti et al, 2006).…”

Remote Control of Gene Expression

“…For example, a kanamycin cassette flanked with flp recombinase target sites was used to target an upstream region of the Sclerostin gene in a 170-kb BAC, and deletion of this region led to a severe decrease in Sclerostin expression (43). Similarly, by combining artificial chromosomes with comparative genomics and homologous recombination, researchers have demonstrated a critical role for distal enhancers in the control of a cluster of odorant receptors (44), the expression of interferon ␥ (45), and the cell-restricted expression of the Tyrosinase gene (46). Although the incorporation of such alterations in an artificial chromosome is rather straightforward, great care is needed to ensure that any changes are restricted to only the target site of interest.…”

Metamodels and Phylogenetic Replication: A Systematic Approach to the Evolution of Developmental Pathways

“…Tyrosinase is expressed in multiple cell types, and its expression is controlled by several tissue-specific enhancers. In particular, different cis-regulatory elements activate Tyrosinase expression in melanocytes and RPE Murisier et al , 2007a. The melanocyte enhancer is co-activated by MITF and Sox10 (Murisier et al 2007b).…”