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Journal of Virology, January 2004, p. 733-740, Vol. 78, No. 2
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.2.733-740.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Expansion of a Unique Region in the Marek's Disease Virus Genome Occurs Concomitantly with Attenuation but Is Not Sufficient To Cause Attenuation

R. F. Silva,* S. M. Reddy,{dagger} and B. Lupiani

Avian Disease and Oncology Laboratory, Agricultural Research Service, U.S. Department of Agriculture, East Lansing, Michigan 48823

Received 11 August 2003/ Accepted 6 October 2003

Pathogenic Marek's disease viruses (MDVs) have two head-to-tail copies of a 132-bp repeat. As MDV is serially passaged in cell culture, the virus becomes attenuated and the number of copies of the 132-bp repeat increases from 2 to often more than 20 copies. To determine the role of the repeats in attenuation, we used five overlapping cosmid clones that spanned the MDV genome to reconstitute infectious virus (rMd5). By mutating the appropriate cosmids, we generated clones of infectious MDVs that contained zero copies of the 132-bp repeats, rMd5({Delta}132); nine copies of the 132-bp repeats, rMd5(9-132); and nine copies of the 132-bp repeats inserted in the reverse orientation, rMd5(rev9-132). After two passages in cell culture, wild-type Md5, rMd5, and rMd5({Delta}132) were stable. However, rMd5(9-132) and rMd5(rev9-132) contained a population of viruses that contained from 3 to over 20 copies of the repeats. A major 1.8-kb mRNA, containing two copies of the 132-bp repeat, was present in wild-type Md5 and rMd5 but was not present in rMd5({Delta}132), rMd5(9-132), rMd5(rev9-132), or an attenuated MDV. Instead, the RNAs transcribed from the 132-bp repeat region in rMd5(9-132) and rMd5(rev9-132) closely resembled the pattern of RNAs transcribed in attenuated MDVs. When inoculated into susceptible day-old chicks, all viruses produced various lesions. Thus, expansion of the number of copies of 132-bp repeats, which accompanies attenuation, is not sufficient in itself to attenuate pathogenic MDVs.

* Corresponding author. Mailing address: Avian Disease and Oncology Laboratory, Agricultural Research Service, U.S. Department of Agriculture, 3606 East Mount Hope Rd., East Lansing, MI 48823. Phone: (517) 337-6833. Fax: (517) 337-6776. E-mail. silvar{at}msu.edu.

{dagger} Present address: Department of Pathobiology, College of Veterinary Medicine, Texas A&M University, College Station, TX 77843.

Journal of Virology, January 2004, p. 733-740, Vol. 78, No. 2
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.2.733-740.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Baigent, S. J., Smith, L. P., Currie, R. J. W., Nair, V. K. (2005). Replication kinetics of Marek's disease vaccine virus in feathers and lymphoid tissues using PCR and virus isolation. J. Gen. Virol. 86: 2989-2998 [Abstract] [Full Text]  
  • Jarosinski, K. W., Osterrieder, N., Nair, V. K., Schat, K. A. (2005). Attenuation of Marek's Disease Virus by Deletion of Open Reading Frame RLORF4 but Not RLORF5a. J. Virol. 79: 11647-11659 [Abstract] [Full Text]  


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