Biomedical subjects

Sabrina Guichard

Publications and source records attributed to Sabrina Guichard.

3 recordsLinked to original sources

PubMed2006

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

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.

Albinism, Oculocutaneous↗

PubMed2006

A conserved transcriptional enhancer that specifies Tyrp1 expression to melanocytes.

Pigment cells of mammals originate from two different lineages: melanocytes arise from the neural crest, whereas cells of the retinal pigment epithelium (RPE) originate from the optic cup of the developing forebrain. Previous studies have suggested that pigmentation genes are controlled by different regulatory networks in melanocytes and RPE. The promoter of the tyrosinase-related family gene Tyrp1 has been shown to drive detectable transgene expression only to the RPE, even though the gene is also expressed in melanocytes as evident from Tyrp1-mutant mice. This indicates that the regulatory elements responsible for Tyrp1 gene expression in the RPE are not sufficient for expression in melanocytes. We thus searched for a putative melanocyte-specific regulatory sequence and demonstrate that a bacterial artificial chromosome (BAC) containing the Tyrp1 gene and surrounding sequences is able to target transgenic expression to melanocytes and to rescue the Tyrp1b (brown) phenotype. This BAC contains several highly conserved non-coding sequences that might represent novel regulatory elements. We further focused on a sequence located at -15 kb, which we identified as a melanocyte-specific enhancer as shown by cell culture and transgenic mice experiments. In addition, we show that the transcription factor Sox10 can activate this conserved enhancer. The presence of a distal Tyrp1 regulatory element, which specifies melanocyte-specific expression, supports the idea that separate regulatory sequences can mediate differential gene expression in melanocytes and RPE.

Animals↗

PubMed2006

Tissue-specific transgenic and knockout mice.

Analysis of genetically engineered mice is crucial for our understanding of the in vivo function of genes and proteins in the whole organism. This includes inactivation of a gene or the generation of specific mutations. The development of knockout and transgenic technologies in the mouse, therefore, represents a powerful tool for elucidating gene function, for modeling of human diseases, and potentially for the evaluation of drugs. In particular, conditional gene targeting applying the Cre/loxP-mediated recombination system is increasingly used to evaluate the role of the gene of interest in a cell-type-specific or even inducible manner. The experimental steps start with the characterization of the gene locus, followed by construction of a vector, gene targeting in ES cells, and establishment of mouse lines carrying the desired mutation. These are then bred to transgenic mice expressing Cre recombinase in a tissue-specific manner, thus allowing gene inactivation in a cell type of interest.

Animals↗