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Emerging roles of chicken and viral microRNAs in avian disease.

Burnside J, Morgan R - BMC Proc (2011)

Bottom Line: For a given viral species the microRNA sequence is highly conserved in different strains with the exception of a virulence-associated polymorphism in the putative promoter of the MDV1 microRNAs upstream of the meq oncogene.These microRNAs are relatively highly expressed in tumors produced by very virulent MDV1 isolates compared to tumors produced by less virulent strains.MicroRNAs are highly conserved among different field strains of MDV1, and they are expressed in lytic and latent infections and in MDV1-derived tumors.

View Article: PubMed Central - HTML - PubMed

Affiliation: Delaware Biotechnology Institute, University of Delaware, 15 Innovation Way, Newark, Delaware 19711, USA. joan@udel.edu.

ABSTRACT

Background: MicroRNAs are short RNAs (~22 nt) expressed by plants, animals and viruses that regulate gene expression post-transcriptionally, and their importance is highlighted by distinct patterns of expression in many physiological processes, including development, hematopoeisis, stress resistance, and disease. Our group has characterized the microRNAs encoded by the avian herpesviruses; namely, oncogenic Marek's disease (MD) virus (MDV1), non-oncogenic MDV (MDV2) herpesvirus of turkeys (HVT), and infectious laryngotracheitis virus (ILTV).

Methods: MicroRNAs encoded by the avian herpesviruses were identified using next generation sequencing technologies (454, Illumina).

Results: The microRNAs of each the avian herpesviruses have unique sequences, but the genomic locations are similar, in that the microRNAs tend to be clustered in the rapidly evolving repeat regions of the viral genomes. For a given viral species the microRNA sequence is highly conserved in different strains with the exception of a virulence-associated polymorphism in the putative promoter of the MDV1 microRNAs upstream of the meq oncogene. These microRNAs are relatively highly expressed in tumors produced by very virulent MDV1 isolates compared to tumors produced by less virulent strains. MDV1 and HVT encode homologs of the host microRNA, miR-221, which targets a gene important in cell cycle regulation. MDV1 encodes a microRNA (mdv1-miR-M4) that shares a seed sequence with miR-155, a microRNA important in immune function. Mdv-miR-M4 is highly expressed in MDV induced tumors, while miR-155 is present at very low levels.

Conclusions: MicroRNAs are highly conserved among different field strains of MDV1, and they are expressed in lytic and latent infections and in MDV1-derived tumors. This suggests that these small molecules are very important to the virus, and roles in immune evasion, anti-apoptosis, or proliferation are likely.

No MeSH data available.


Related in: MedlinePlus

Schematic representation of avian herpesviruses and location of clusters of microRNAs. Terminal and internal short and long repeats are designated TRS, IRS, TRL and TRS. The approximate location and direction of transcription of microRNA clusters are indicated by the arrows. Lengths of each region are not drawn to scale.
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Figure 1: Schematic representation of avian herpesviruses and location of clusters of microRNAs. Terminal and internal short and long repeats are designated TRS, IRS, TRL and TRS. The approximate location and direction of transcription of microRNA clusters are indicated by the arrows. Lengths of each region are not drawn to scale.

Mentions: Our laboratory has identified microRNAs encoded by four avian herpesviruses, MDV1, MDV2, HVT, and ILTV [13,14]. Like other herpesviruses, the genome of the avian herpesviruses contains unique long (UL) and unique short (US) regions that are flanked by terminal and internal repeats (I/TRL; I/TRS). The unique regions contain functionally conserved protein coding sequences, while the repeats generally encode virus-specific genes. The avian herpesvirus microRNAs tend to be clustered in these highly plastic, repeat regions (Figure 1). In accordance with these being virus-specific regions, there is no conservation of sequence among any of the microRNAs from the different viruses. We have speculated that the viral microRNAs appeared with the evolution of the repeat regions, suggesting that the function of the microRNAs is to provide an advantage to the virus, and if their acquisition produced a loss-of-function, this could be complemented by sequences in the other repeat. Gain-of-function mutations, however, would be maintained and eventually duplicated.


Emerging roles of chicken and viral microRNAs in avian disease.

Burnside J, Morgan R - BMC Proc (2011)

Schematic representation of avian herpesviruses and location of clusters of microRNAs. Terminal and internal short and long repeats are designated TRS, IRS, TRL and TRS. The approximate location and direction of transcription of microRNA clusters are indicated by the arrows. Lengths of each region are not drawn to scale.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3108214&req=5

Figure 1: Schematic representation of avian herpesviruses and location of clusters of microRNAs. Terminal and internal short and long repeats are designated TRS, IRS, TRL and TRS. The approximate location and direction of transcription of microRNA clusters are indicated by the arrows. Lengths of each region are not drawn to scale.
Mentions: Our laboratory has identified microRNAs encoded by four avian herpesviruses, MDV1, MDV2, HVT, and ILTV [13,14]. Like other herpesviruses, the genome of the avian herpesviruses contains unique long (UL) and unique short (US) regions that are flanked by terminal and internal repeats (I/TRL; I/TRS). The unique regions contain functionally conserved protein coding sequences, while the repeats generally encode virus-specific genes. The avian herpesvirus microRNAs tend to be clustered in these highly plastic, repeat regions (Figure 1). In accordance with these being virus-specific regions, there is no conservation of sequence among any of the microRNAs from the different viruses. We have speculated that the viral microRNAs appeared with the evolution of the repeat regions, suggesting that the function of the microRNAs is to provide an advantage to the virus, and if their acquisition produced a loss-of-function, this could be complemented by sequences in the other repeat. Gain-of-function mutations, however, would be maintained and eventually duplicated.

Bottom Line: For a given viral species the microRNA sequence is highly conserved in different strains with the exception of a virulence-associated polymorphism in the putative promoter of the MDV1 microRNAs upstream of the meq oncogene.These microRNAs are relatively highly expressed in tumors produced by very virulent MDV1 isolates compared to tumors produced by less virulent strains.MicroRNAs are highly conserved among different field strains of MDV1, and they are expressed in lytic and latent infections and in MDV1-derived tumors.

View Article: PubMed Central - HTML - PubMed

Affiliation: Delaware Biotechnology Institute, University of Delaware, 15 Innovation Way, Newark, Delaware 19711, USA. joan@udel.edu.

ABSTRACT

Background: MicroRNAs are short RNAs (~22 nt) expressed by plants, animals and viruses that regulate gene expression post-transcriptionally, and their importance is highlighted by distinct patterns of expression in many physiological processes, including development, hematopoeisis, stress resistance, and disease. Our group has characterized the microRNAs encoded by the avian herpesviruses; namely, oncogenic Marek's disease (MD) virus (MDV1), non-oncogenic MDV (MDV2) herpesvirus of turkeys (HVT), and infectious laryngotracheitis virus (ILTV).

Methods: MicroRNAs encoded by the avian herpesviruses were identified using next generation sequencing technologies (454, Illumina).

Results: The microRNAs of each the avian herpesviruses have unique sequences, but the genomic locations are similar, in that the microRNAs tend to be clustered in the rapidly evolving repeat regions of the viral genomes. For a given viral species the microRNA sequence is highly conserved in different strains with the exception of a virulence-associated polymorphism in the putative promoter of the MDV1 microRNAs upstream of the meq oncogene. These microRNAs are relatively highly expressed in tumors produced by very virulent MDV1 isolates compared to tumors produced by less virulent strains. MDV1 and HVT encode homologs of the host microRNA, miR-221, which targets a gene important in cell cycle regulation. MDV1 encodes a microRNA (mdv1-miR-M4) that shares a seed sequence with miR-155, a microRNA important in immune function. Mdv-miR-M4 is highly expressed in MDV induced tumors, while miR-155 is present at very low levels.

Conclusions: MicroRNAs are highly conserved among different field strains of MDV1, and they are expressed in lytic and latent infections and in MDV1-derived tumors. This suggests that these small molecules are very important to the virus, and roles in immune evasion, anti-apoptosis, or proliferation are likely.

No MeSH data available.


Related in: MedlinePlus