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bioRxiv · 10.1101/077065

A structural variant in the 5′-flanking region of the TWIST2 gene affects melanocyte development in belted cattle

Niveditha Awasthi Mishra·Cord Drögemüller·Vidhya Jagannathan·Rémy Bruggmann·Julia Beck·Ekkehard Schütz·Bertram Brenig·Steffi Demmel·Simon Moser·Heidi Signer-Hasler·Aldona Pieńkowska-Schelling·Claude Schelling·Ronald Rongen·Stefan Rieder·Robert N. Kelsh·Nadia Mercader·Tosso Leeb
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Abstract

Belted cattle have a circular belt of unpigmented hair and skin around their midsection. The belt is inherited as a monogenic autosomal dominant trait. We mapped the causative variant to a 54 kb segment on bovine chromosome 3. Whole genome sequence data of 2 belted and 130 control cattle yielded only one private genetic variant in the critical interval in the two belted animals. The belt-associated variant was a copy number variant (CNV) involving the quadruplication of a 6 kb non-coding sequence located approximately 16 kb upstream of the TWIST2 gene. Increased copy numbers at this CNV were strongly associated with the belt phenotype in a cohort of 239 cases and 1303 controls (p = 1.3 x 10-278). We hypothesized that the CNV causes aberrant expression of TWIST2 during neural crest development, which might negatively affect melanoblasts. Functional studies showed that ectopic expression of bovine TWIST2 in neural crest in transgenic zebrafish led to a decrease in melanocyte numbers. Our results thus implicate an unsuspected involvement of TWIST2 in regulating pigmentation and reveal a non-coding CNV underlying a captivating Mendelian character.\n\nAuthor SummaryBelted cattle, a spontaneous coat color mutant, have been recognized at least 600 years ago. The striking pigmentation pattern probably has arisen in medieval cattle of the Alpine region. The belt still segregates in Brown Swiss cattle and it has become a breed-defining character in the Lakenvelder or Dutch Belted cattle. The belted allele has also been introgressed into Galloways to form the Belted Galloways. We report here the causative genetic variant, a non-coding copy number variant (CNV) upstream of the TWIST2 gene. We hypothesize that the CNV leads to ectopic expression of TWIST2 in the neural crest, which negatively affects melanocyte development. Overexpression of bovine TWIST2 in transgenic zebrafish embryos led to a decrease in melanocyte numbers, which provides functional support for our hypothesis.

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Niveditha Awasthi Mishra, Cord Drögemüller, Vidhya Jagannathan, Rémy Bruggmann, Julia Beck, Ekkehard Schütz, Bertram Brenig, Steffi Demmel, Simon Moser, Heidi Signer-Hasler, Aldona Pieńkowska-Schelling, Claude Schelling, Ronald Rongen, Stefan Rieder, Robert N. Kelsh, Nadia Mercader, Tosso Leeb. 2016-09-23. A structural variant in the 5′-flanking region of the TWIST2 gene affects melanocyte development in belted cattle. https://doi.org/10.1101/077065

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