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      Familiar Hypopigmentation Syndrome in Sheep Associated with Homozygous Deletion of the Entire Endothelin Type-B Receptor Gene

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          In humans, rodents and horses, pigmentary anomalies in combination with other disorders, notably intestinal aganglionosis, are associated with variants of the endothelin type-B receptor gene ( EDNRB). In an inbred Cameroon sheep flock, five white lambs with light blue eyes were sired from the same ram and died within a few hours up to a few days after birth, some of them with signs of intestinal obstruction. The aim of this study was to investigate if the observed hypopigmentation and a possible lethal condition were associated with a molecular change at the ovine EDNRB locus, and to check if such a genetic alteration also occurs in other Cameroon sheep flocks. Sequence analysis revealed a deletion of about 110 kb on sheep chromosome 10, comprising the entire EDNRB gene, on both chromosomes in the two available hypopigmented lambs and on a single chromosome in the two dams and three other unaffected relatives. This micro-chromosomal deletion was also confirmed by quantitative real-time PCR and by fluorescence in situ hybridization. Genotyping of a total of 127 Cameroon sheep in 7 other flocks by duplex PCR did not identify additional carriers of the deletion. Although both hypopigmented lambs available for post-mortem examination had a considerably dilated cecum and remaining meconium, histopathological examination of intestinal samples showed morphologically normal ganglion cells in appropriate number and distribution. This is to our knowledge the first description of an ENDRB gene deletion and associated clinical signs in a mammalian species different from humans and rodents. In humans and rats it is postulated that the variable presence and severity of intestinal aganglionosis and other features in individuals with EDNRB deletion is due to a variable genetic background and multiple gene interactions. Therefore the here analyzed sheep are a valuable animal model to test these hypotheses in another species.

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          Most cited references 32

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          Targeted and natural (piebald-lethal) mutations of endothelin-B receptor gene produce megacolon associated with spotted coat color in mice.

          Endothelins act on two subtypes of G protein-coupled receptors, termed endothelin-A and endothelin-B receptors. We report a targeted disruption of the mouse endothelin-B receptor (EDNRB) gene that results in aganglionic megacolon associated with coat color spotting, resembling a hereditary syndrome of mice, humans, and other mammalian species. Piebald-lethal (sl) mice exhibit a recessive phenotype identical to that of the EDNRB knockout mice. In crossbreeding studies, the two mutations show no complementation. Southern blotting revealed a deletion encompassing the entire EDNRB gene in the sl chromosome. A milder allele, piebald (s), which produces coat color spotting only, expresses low levels of structurally intact EDNRB mRNA and protein. These findings indicate an essential role for EDNRB in the development of two neural crest-derived cell lineages, myenteric ganglion neurons and epidermal melanocytes. We postulate that defects in the human EDNRB gene cause a hereditary form of Hirschsprung's disease that has recently been mapped to human chromosome 13, in which EDNRB is located.
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            Waardenburg syndrome.

             A P Read,  V Newton (1997)
            Auditory-pigmentary syndromes are caused by physical absence of melanocytes from the skin, hair, eyes, or the stria vascularis of the cochlea. Dominantly inherited examples with patchy depigmentation are usually labelled Waardenburg syndrome (WS). Type I WS, characterised by dystopia canthorum, is caused by loss of function mutations in the PAX3 gene. Type III WS (Klein-Waardenburg syndrome, with abnormalities of the arms) is an extreme presentation of type I; some but not all patients are homozygotes. Type IV WS (Shah-Waardenburg syndrome with Hirschsprung disease) can be caused by mutations in the genes for endothelin-3 or one of its receptors, EDNRB. Type II WS is a heterogeneous group, about 15% of whom are heterozygous for mutations in the MITF (microphthalmia associated transcription factor) gene. All these forms show marked variability even within families, and at present it is not possible to predict the severity, even when a mutation is detected. Characterising the genes is helping to unravel important developmental pathways in the neural crest and its derivatives.
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              Null mutation of endothelin receptor type B gene in spotting lethal rats causes aganglionic megacolon and white coat color.

              Mutations in the gene encoding the endothelin receptor type B (EDNRB) produce congenital aganglionic megacolon and pigment abnormalities in mice and humans. Here we report a naturally occurring null mutation of the EDNRB gene in spotting lethal (sl) rats, which exhibit aganglionic megacolon associated with white coat color. We found a 301-bp deletion spanning the exon 1-intron 1 junction of the EDNRB gene in sl rats. A restriction fragment length polymorphism caused by this deletion perfectly cosegregates with the sl phenotype. The deletion leads to production of an aberrantly spliced EDNRB mRNA that lacks the coding sequence for the first and second putative transmembrane domains of the G-protein-coupled receptor. Radioligand binding assays revealed undetectable levels of functional EDNRB in tissues from homozygous sl/sl rats. We conclude that EDNRB plays an essential role in the normal development of two neural crest-derived cell lineages, epidermal melanocytes and enteric neurons, in three mammalian species--humans, mice, and rats. The EDNRB-deficient rat may also prove valuable in defining the postnatal physiologic role of this receptor.

                Author and article information

                Role: Editor
                PLoS One
                PLoS ONE
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                31 December 2012
                : 7
                : 12
                [1 ]Department of Animal Breeding and Genetics, Justus-Liebig University of Giessen, Giessen, Germany
                [2 ]Institute of Veterinary Pathology, Justus-Liebig University of Giessen, Giessen, Germany
                Institut Jacques Monod, France
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Conceived and designed the experiments: GL AP GE. Performed the experiments: KF MH AP. Analyzed the data: GL KF AP. Contributed reagents/materials/analysis tools: GL AP GE. Wrote the paper: GL KF AP. Revised the article critically for important intellectual content: MH GE. Gave final approval of the version to be published: all the authors.


                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                Page count
                Pages: 9
                No sources of funding were used.
                Research Article
                Cytogenetic Analysis
                Cytogenetic Techniques
                Molecular Genetics
                Gene Identification and Analysis
                Animal Genetics
                Gene Function
                Genetic Screens
                Genetics of Disease
                Model Organisms
                Animal Models
                Clinical Genetics
                Autosomal Recessive
                Veterinary Science
                Veterinary Pathology



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