Microevolução in vitro do vírus dengue, sorotipo-4: estudo de variações genéticas associadas ao aumento da competência viral

Abstract

Dengue virus (DENV) belongs to the family Flaviviridae and the genus Flavivirus, being recognized as four distinct serotypes termed DENV-1 to DENV-4. Like other RNA viruses, DENV displays variation in their sequences, with an error rate during replication cycle estimated at 10-3 to 10-5 errors / nucleotide. These variations are observed not only when samples from different individuals are analyzed, but also within the same host. Considering the need for a better understanding of related mechanisms of DENV evolutionary process and the emergence of viral subpopulations, this study aimed to evaluate the in vitro microevolution of dengue virus serotype-4, analyzing the existence of genetic variations associated with increased viral fitness. For this purpose, a sample of DENV-4 called BR005AM_2015 was inoculated in C6/36 cells and 25 serial passages were performed. After these passages, viral RNA extraction was performed and the cDNA was produced using a specificDENV-4 primer. The full-length genome of the sample BR005AM_2015 and passages 1, 5, 10, 15, 20 and 25 were obtained by the Sanger method using the ABI 3130 Genetic Analyzer and by Next-Generation Sequencing (NGS) using the Ion Torrent technology. The files generated after the sequencing reactions were analyzed using Geneious software version 7.1.7. The analysis of the data provided by the Sanger sequencing has shown that during the 25 passages, two nucleotide mutations occurred, one in the region which encodes for the envelope protein, resulting in the substitution of an amino acid residue T501P, and other silent mutation at NS1 gene. The results of NGS corroborate those obtained by Sanger sequencing. Moreover, seventeen other mutations not previously observed, being the same in the coding regions for proteins E, NS1, NS2A, NS2B, NS3, NS4A, NS4B and NS5. Of the total observed mutations, six of them led to residue substitution. Considering the observed amino acids substitutions, we conducted a study of viral kinetics by RT-qPCR using the ΔΔCt method which indicated a time-dependent increase in the number of copies of viral RNA present in both the supernatant or inside the infected cells, indicating a possible increase of the viral fitness. Other studies are necessary to confirm if the mutations described here also occurs in mammalian cells or in vivo systems, as well as to verify if the observed increase in viral fitness occurs in other systems.