Establishment and evaluation of the goose embryo epithelial (GEE) cell line as a new model for propagation of avian viruses

Establishment of reverse genetics for genotype VII Newcastle disease virus and altering the cell tropism by inserting TMPRSS2 into the viral genome

Newcastle disease (ND) is the most important infectious disease in poultry, which is caused by avian orthoavulavirus type 1 (AOAV-1), previously known as Newcastle disease virus (NDV). In this study, an NDV strain SD19 (GenBank accession number OP797800) was isolated, and phylogenetic analysis suggested the virus belongs to the class II genotype VII. After generating wild-type rescued SD19 (rSD19), the attenuating strain (raSD19) was generated by mutating the F protein cleavage site. To explore the potential role of the transmembrane protease, serine S1 member 2 (TMPRSS2), the TMPRSS2 gene was inserted into the region between the P and M genes of raSD19 to generate raSD19-TMPRSS2. Besides, the coding sequence of the enhanced green fluorescent protein (EGFP) gene was inserted in the same region as a control (rSD19-EGFP and raSD19-EGFP). The Western blot, indirect immunofluorescence assay (IFA), and real-time quantitative PCR were employed to determine the replication activity of these constructs. The results reveal that all the rescued viruses can replicate in chicken embryo fibroblast (DF-1) cells; however, the proliferation of raSD19 and raSD19-EGFP needs additional trypsin. We next evaluated the virulence of these constructs, and our results reveal that the SD19, rSD19, and rSD19-EGFP are velogenic; the raSD19 and raSD19-EGFP are lentogenic; and the raSD19-TMPRSS2 are mesogenic. Moreover, due to the enzymatic hydrolysis of serine protease, the raSD19-TMPRSS2 can support itself to proliferate in the DF-1 cells without adding exogenous trypsin. These results may provide a new method for the NDV cell culture and contribute to ND's vaccine development.

Current status and future direction of duck hepatitis A virus vaccines

Duck viral hepatitis (DVH), mainly caused by duck hepatitis A virus (DHAV), is a highly fatal and rapidly spreading infectious disease of young ducklings that seriously jeopardizes the duck industry worldwide. DHAV type 1 (DHAV-1) is the main genotype responsible for disease outbreaks since 1945, and the disease situation is complicated by the emergence and dissemination of a novel genotype (DHAV-3) in some countries in Asia and Africa. Live attenuated DHAV vaccines are widely used to induce a considerable degree of protection in ducklings. Breeder ducks are immunized with inactivated or/and live DHAV vaccines to achieve satisfactory levels of passive immunity in progeny. In addition, novel characteristics of virus transmission, pathogenicity and pathogenesis of DHAV were recently characterized, necessitating the development of new vaccines and effective vaccination programmes against DVH. Therefore, a systematic dissection of the profiles, strengths and shortcomings of the available DHAV vaccines is essential. Moreover, to further increase the efficiency of vaccine production and administration, the development of next-generation DHAV vaccines using cutting-edge technologies is also required. In this review, based on a comprehensive summary of the research advances in the epidemiology, pathogenicity, and genomic features of DHAV, we focus on reviewing and analysing the features of the commercial and experimental DHAV vaccines. We also propose perspectives for disease control based on the specific disease situations in different countries. This review provides essential information for vaccine development and disease control of DVH.

Establishment methods and research progress of livestock and poultry immortalized cell lines: A review

An infinite cell line is one of the most favored experimental tools and plays an irreplaceable role in cell-based biological research. Primary cells from normal animal tissues undergo a limited number of divisions and subcultures in vitro before they enter senescence and die. On the contrary, an infinite cell line is a population of non-senescent cells that could proliferate indefinitely in vitro under the stimulation of external factors such as physicochemical stimulation, virus infection, or transfer of immortality genes. Cell immortalization is the basis for establishing an infinite cell line, and previous studies have found that methods to obtain immortalized cells mainly included physical and chemical stimulations, heterologous expression of viral oncogenes, increased telomerase activity, and spontaneous formation. However, some immortalized cells do not necessarily proliferate permanently even though they can extend their lifespan compared with primary cells. An infinite cell line not only avoids the complicated process of collecting primary cell, it also provides a convenient and reliable tool for studying scientific problems in biology. At present, how to establish a stable infinite cell line to maximize the proliferation of cells while maintaining the normal function of cells is a hot issue in the biological community. This review briefly introduces the methods of cell immortalization, discusses the related progress of establishing immortalized cell lines in livestock and poultry, and compares the characteristics of several methods, hoping to provide some ideas for generating new immortalized cell lines.

Establishment of the Primary Avian Gonadal Somatic Cell Lines for Cytogenetic Studies

Simple Summary

We developed a simple method for primary somatic cell culture establishment from the ovaries of the great tits and testes of ten Passerine species. The ovary-derived cell cultures were cultivated until the tenth passage without any noticeable decrease in their proliferative activity, while testis-derived cell cultures demonstrated a decreased proliferation potential. However, sufficient material was available from both cell cultures originating from the ovary and testis to make excellent mitotic metaphase chromosomal preparations. We demonstrated the high efficiency of electroporation for genetic modification of the ovary-derived cell line. Thus, the established ovary-derived cell line could be efficiently used in cytogenetic and genomic studies.

Abstract

The last decade was marked by a steep rise in avian studies at genomic and cellular levels. Cell lines are important tools for in vitro studies in cell biology and cytogenetics. We developed a simple method of primary somatic cell culture establishment from the ovaries of the great tits (Parus major) and testes of ten Passerine species, characterized the cellular composition of the ovary-derived lines using RT-PCR and immunolocalization of the tissue-specific markers and tested the efficiency of two methods of genetic transformation of the ovary-derived cell line. We found that the ovary-derived cell cultures of the great tit were composed of fibroblasts mainly, but also contained interstitial and granulosa cells. They were cultivated until the 10th passage without any noticeable decrease in their proliferative activity. The testis-derived cell cultures had lower proliferative potential. However, both ovary- and testis-derived cell cultures provided enough material for high quality mitotic metaphase chromosome preparations. The efficiency of its transduction with lentivirus containing a GFP reporter was very low, while electroporation with episomal vectors expressing GFP resulted in a high yield of GFP-positive cells. The proposed method could be used for the generation of high quality material for various cytogenetic and genomic studies.

Biochemical characterization of recombinant Avihepatovirus 3C protease and its localization

BACKGROUND

The picornaviral 3C protease mediates viral polyprotein maturation and multiple cleavages of host proteins to modulate viral translation and transcription. The 3C protease has been regarded as a valid target due to its structural similarity among different picornaviruses and minimal sequence similarity with host proteins; therefore, the development of potent inhibitors against the 3C protease as an antiviral drug is ongoing. Duck hepatitis A virus (DHAV) belongs to the Picornavidea family and is a major threat to the poultry industry. To date, little is known about the roles of the DHAV 3C protease plays during infection.

METHODS

In this study, we compared the full-length DHAV 3C protein sequence with other 3C sequences to obtain an alignment for the construction of a phylogenetic tree. Then, we expressed and purified recombinant DHAV 3C protease in the BL21 expression system using nickel-NTA affinity chromatography. The optimization of the cleavage assay conditions and the kinetic analysis for DHAV 3C protease were done by in vitro cleavage assays with a fluorogenic peptide respectively. The inhibitory activity of rupintrivir against the DHAV 3C protease was further evaluated. The localization of the 3C protease in infected and transfected cells was determined using immunofluorescence and confocal microscopy.

RESULTS

Under different expression conditions, the 3C protease was found to be highly expressed after induction with 1 mM IPTG at 16 °C for 10 h. We synthesized a fluorogenic peptide derived from the cleavage site of the DHAV polyprotein and evaluated the protease activity of the DHAV 3C protease for the first time. We used fluorimetric based kinetic analysis to determine kinetic parameters, and Vmax and Km values were determined to be 16.52 nmol/min and 50.78 μM, respectively. Rupintrivir was found to exhibit inhibitory activity against the DHAV 3C protease. Using polyclonal antibody and an indirect immunofluorescence microscopy assay (IFA), it was determined that the DHAV 3C protease was found in the nucleus during infection. In addition, the DHAV 3C protease can enter into the nucleus without the cooperation of viral proteins.

CONCLUSIONS

This is the first study to examine the activity of the DHAV 3C protease, and the activity of the DHAV 3C protease is temperature-, pH- and NaCl concentration- dependent. The DHAV 3C protease localizes throughout DHAV-infected cells and can enter into the nucleus in the absence of other viral proteins. The kinetic analysis was calculated, and the Vmax and Km values were 16.52 nmol/min and 50.78 μM, respectively, using the Lineweaver-Burk plot.