Effects Of F Gene Start Codon Specific Mutation On Biological Characteristics Of NDV La Sota Strain

In recent years,the isolation rate of class ? NDV from poultry has been increased.Our research team previously found that mutations in the start codon of F gene led to the long coding sequence of class ? NDV strains,and demonstrated that ATA mutation at the start codon of F gene could lead to increased virulence of class ? NDV strains,indicating that low virulent NDV strains may mutate into virulent NDV strains.In view of the fact that the genotype ? strain of class ? NDV is widely used for ND vaccination and exists for a long time in the chicken flocks.It is not clear whether similar mutations in the F gene start codon have a potential impact on its biological characteristics.In this study,La Sota,a class ? genotype ? strain,was used as the object to evaluate the potential effect of F gene start codon mutation on the biological characteristics.Firstly,reverse genetics was used to mutate the start codon of F gene in La Sota strain to ATA or CTA.There is one start codon was introduced at 12 and 33 nucleotide positions before the original start codon,respectively.The length of the coding region of F gene was changed to 1674 or 1695 nucleotides,encoding 560 or 564 amino acids,and the plasmids pNDFLsp-ATA and pNDFLsp-CTA were obtained.Then two mutant strains named as La Sota-ATA and La Sota-CTA were obtained by transfecting the constructed plasmid into cells.The MDT of La Sota,La Sota-ATA and La Sota-CTA were 100 h,107.125 h and 119.625 h,respectively,which were all longer than 90 h.The ICPI of La Sota,La Sota-ATA and La Sota-CTA were 0.19,0.1625 and 0.4862,respectively,which were all less than 0.7,which was consistent with the characteristics of low virulence strain,indicating that the mutation of F gene start codon did not affect the virulence of La Sota.La Sota,La Sota-ATA and La Sota-CTA also showed similar growth dynamics in chicken embryos,all of which reached the highest titers at 72 h after inoculation,and there was no significant difference among the three strains.Our previous study found that the mutation of start codon of class ? NDV increased its virulence and replication ability only when it was specifically mutated to ATA.Therefore,the replication ability of the mutant virus La Sota-ATA and its parent virus La Sota in chickens was examined in this study.The results showed that there was no significant difference in viral load between the same tissues in SPF chickens inoculated with La Sota-ATA and La Sota,suggesting that La Sota-ATA and La Sota had similar replication capacity in SPF chickens.In addition,the results showed that the mutation of the F gene start codon in La Sota-ATA and La Sota-CTA did not cause significant changes in the red blood cell(RBC)adsorption activity.However,it can increase the activity of neuraminidase and decrease the activity of hemolysis and membrane fusion.In this study,we mutated the F gene start codon of the class ? genotype ? NDV La Sota,which is widely present in chicken flocks.The potential effect of F gene start codon mutation on the biological characteristics of the virus was further evaluated.The results of this study provide a theoretical basis for the prevention and control of NDV.