The Infectious bronchitis virus D-RNA is an RNA element known as defective RNA or D-RNA. This element is thought to be essential for

viral replication Viral replication is the formation of biological viruses during the infection process in the target host cells. Viruses must first get into the cell before viral replication can occur. Through the generation of abundant copies of its genome an ...

and efficient packaging of

avian infectious bronchitis virus ''Avian coronavirus'' is a species of virus from the genus ''Gammacoronavirus'' that infects birds; since 2018, all gammacoronaviruses which infect birds have been classified as this single species. The strain of avian coronavirus previously kno ...

(IBV) particles. Coronavirus D-RNA like that of IBV, are produced during high

multiplicity of infection In microbiology, the multiplicity of infection or MOI is the ratio of agents (e.g. phage or more generally virus, bacteria) to infection targets (e.g. cell). For example, when referring to a group of cells inoculated with virus particles, the MOI ...

and contain ''cis-''acting sequences which are required for viral replication. While it is unclear exactly how IBV D-RNA is made, it is thought to be synthesized in a similar manner as

subgenomic mRNA Subgenomic mRNAs are essentially smaller sections of the original transcribed template strand. 3' to 5' DNA or RNA During transcription, the original template strand is usually read from the 3' to the 5' end from beginning to end. Subgenomic ...

(sg mRNA), with most of the genomic sequence left out of the product. Additionally, sg mRNA can also be synthesized from the IBV D-RNA, although the mechanism of that process is still largely unknown. IBV D-RNA is often used in the

reverse genetics Reverse genetics is a method in molecular genetics that is used to help understand the function(s) of a gene by analysing the phenotypic effects caused by genetically engineering specific nucleic acid sequences within the gene. The process pr ...

approach to experimentally induce

heterologous The term heterologous has several meanings in biology. Gene expression In cell biology and protein biochemistry, heterologous expression means that a protein is experimentally put into a cell that does not normally make (i.e., express) that ...

gene expression and site-specific

mutagenesis Mutagenesis () is a process by which the genetic information of an organism is changed by the production of a mutation. It may occur spontaneously in nature, or as a result of exposure to mutagens. It can also be achieved experimentally using lab ...

of the coronavirus genome. However, a translation associated sequence (TAS), which is normally used to transcribe sg mRNA and is derived from gene 5 of the Beaudette strain of IBV, is needed as a promoter to regulate heterologous gene expression. It is also thought that TAS may program some IBV D-RNA to synthesize sg mRNA, which are necessary for homologous gene protein synthesis. In particular, IBV D-RNA CD-61 is used to experimentally produce recombinant IBV

vaccine A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. The safety and effectiveness of vaccines has been widely studied and verified.

s. D-RNA CD-61 was created from the naturally occurring IBV D-RNA CD-91, which is produced by multiple passage of high concentration IBV in chick kidney (CK) cells. The IBV D-RNA CD-61 resulted from deletion mutagenesis of CD-91 and lacks much of the genome but retains the sequences necessary for replication and packaging of viral particles in the presence of a helper virus. One particularly promising method of IBV D-RNA-mediated heterologous gene expression uses the helper virus dependent system to promote IBV immunity. The helper virus identifies and responds to signals within the IBV D-RNA that are responsible for replication and packaging of IBV particles. Those sequences are thought to be contained within the 5’ and 3’ UTRs of the D-RNA. Analysis of the packaged IBV particles revealed that leader sequence switching occurs between the D-RNA and the IBV helper viruses, which was similarly observed in

bovine coronavirus Bovine coronavirus (BCV or BCoV) is a coronavirus which is a member of the species ''Betacoronavirus 1''. The infecting virus is an enveloped, positive-sense, single-stranded RNA virus which enters its host cell by binding to the N-acetyl-9- ...

. In addition, it was found that the TAS of the IBV D-RNA contained a consensus sequence that can accept the switched leader sequence and can also be involved in the expression of

mRNA In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of synthesizing a protein. mRNA is created during the ...

from D-RNA. With the helper virus dependent system, chIFN-gamma-containing IBV D-RNA was successfully used to induce the expression of chicken

gamma interferon Interferon gamma (IFN-γ) is a dimerized soluble cytokine that is the only member of the type II class of interferons. The existence of this interferon, which early in its history was known as immune interferon, was described by E. F. Wheelock ...

in IBV-infected CK cells to produce possible immunity against avian IBV, which is a highly infectious

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

of chickens that causes respiratory, reproductive, and growth complications. It was also shown that biologically active chIFN-gamma was secreted into the allantonic fluid of chicken embryos ''

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...

,'' showing that induction of

cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrin ...

s and, therefore, an immune response, can be induced in living organisms in addition to cultured cells. The use of IBV D-RNA as a

vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...

to create vaccines for IBV is of economic significance. Due to the IBV

tropism A tropism is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, this response is dependent on the direction of the stimulus (as oppos ...

which specifically targets chickens, recombinant IBV vaccines may provide economical security for poultry farms responsible for egg and meat production around the world.

References

External links

* {{Rfam, id=RF00385, name=Infectious bronchitis virus D-RNA Cis-regulatory RNA elements Gammacoronaviruses

See also

References

External links