Open Access
Vet. Res.
Volume 38, Number 3, May-June 2007
Page(s) 419 - 433
Published online 13 March 2007
How to cite this article Vet. Res. (2007) 419-433
Vet. Res. 38 (2007) 419-433
DOI: 10.1051/vetres:2007009

A full UL13 open reading frame in Marek's disease virus (MDV) is dispensable for tumor formation and feather follicle tropism and cannot restore horizontal virus transmission of rRB-1B in vivo

Caroline Blondeaua, Najet Chbaba, b, Catherine Beaumontc, Katia Courvoisiera, Nikolaus Osterriederb, Jean-François Vautherota and Caroline Denesvrea

a  INRA, Laboratoire Virologie Moléculaire, UR1282, Infectiologie Animale et Santé Publique, IASP, 37380 Nouzilly, France
b  Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
c  INRA, UR83, Unité de Recherche Avicole, 37380 Nouzilly, France

(Received 29 September 2006; accepted 8 December 2006; published online 13 March 2007)

Abstract - Marek's disease virus (MDV) is an oncogenic alphaherpesvirus that is highly contagious in poultry. Recombinant RB-1B (rRB-1B) reconstituted from an infectious genome cloned as a bacterial artificial chromosome (BAC) is unable to spread horizontally, quite in contrast to parental RB-1B. This finding suggests the presence of one or several mutations in cloned relative to parental viral DNA. Sequence analyses of the pRB-1B bacmid identified a one-nucleotide insertion in the UL13 orthologous gene that causes a frame-shift mutation and thereby results in a theoretical truncated UL13 protein (176 aa vs. 513 aa in parental RB-1B). UL13 genes are conserved among alphaherpesviruses and encode protein kinases. Using two-step "en passant" mutagenesis, we restored the UL13 ORF in pRB-1B. After transfection of UL13-positive pRB-1B DNA (pRB-1B*UL13), the resulting, repaired virus did not exhibit a difference in cell-to cell spread (measured by plaque sizes) and in UL13 transcripts in culture compared to parental rRB-1B virus. Although 89% of the chickens inoculated with rRB-1B*UL13 virus developed tumors in visceral organs, none of the contact birds did. MDV antigens were clearly expressed in the feather tips of rRB-1B infected chickens, suggesting that the UL13 gene mutation did not alter virus tropism of the feather follicle. The results indicate that the correction in UL13 gene alone is not sufficient to restore in vivo spreading capabilities of the rRB-1B virus, and that other region(s) of pRB-1B might be involved in the loss-of-function phenotype. This finding also shows for the first time that a full UL13 ORF is dispensable for MDV tumor formation and feather follicle tropism.

Key words: Marek's disease virus / UL13 / pathogenesis / horizontal spread / chicken

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© INRA, EDP Sciences 2007