Retroviral Recombination In Vivo: Viral Replication Patterns and Genetic Structure of Simian Immunodeficiency Virus (SIV) Populations in Rhesus Macaques after Simultaneous or Sequential Intravaginal Inoculation with SIVmac239Δvpx/Δvpr and SIVmac239Δnef

To characterize the occurrence, frequency, and kinetics of retroviral recombination in vivo, we intravaginally inoculated rhesus macaques, either simultaneously or sequentially, with attenuated simian immunodeficiency virus (SIV) strains having complementary deletions in their accessory genes and various degrees of replication impairment. In monkeys inoculated simultaneously with SIVmac239Δvpx/Δvpr and SIVmac239Δnef, recombinant wild-type (wt) virus and wild-type levels of plasma viral RNA (vRNA) were detected in blood by 2 weeks postinoculation. In monkeys inoculated first with SIVmac239Δvpx/Δvpr and then with SIVmac239Δnef, recombination occurred but was associated with lower plasma vRNA levels than plasma vRNA levels seen for monkeys inoculated intravaginally with wt SIVmac239. In one monkey, recombination occurred 6 weeks after the challenge with SIVmac239Δnef when plasma SIVmac239Δvpx/Δvpr RNA levels were undetectable. In monkeys inoculated first with the more highly replicating strain, SIVmac239Δnef, and then with SIVmac239Δvpx/Δvpr, wild-type recombinant virus was not detected in blood or tissues. Instead, a virus that had repaired the deletion in the nef gene by a compensatory mutation was found in one animal. Overall, recombinant SIV was eventually found in four of six animals intravaginally inoculated with the two SIVmac239 deletion mutants. These findings show that recombination can occur readily in vivo after mucosal SIV exposure and thus contributes to the generation of viral genetic diversity and enhancement of viral fitness

Remote sensing of homochirality: A proxy for the detection of extraterrestrial life

Homochirality is an exclusive feature of life on Earth. Although the very basic building blocks of life, such as sugars and amino acids, are common in the universe, they almost exclusively occur in only one enantiomeric form. It is assumed that homochirality is universal for all lives and is therefore a potentially very unambiguous biosignature. The detection of homochirality by polarization could prove to be a powerful technique complementary to other remote life-detection strategies. In this chapter, we will give a small overview of the homochirality of life as we know it and review some of the theories behind the origin of life. Thereafter, we will discuss the framework that allows comparison between different types of measurements and we will review the most important mechanisms contributing to the optical phenomena displayed by homochiral molecules. Finally, we will discuss the polarimetry and wavelength considerations for the remote sensing of homochirality and we will point out current and future instrumental possibilities and constraints