Retroviruses are unique for their ability to permanently insert their genetic material into the DNA of host cells, he said. During evolution of mammals, some retroviruses infected the germline (cells of the ovary and testis that have genetic material that are passed to their offspring) of the host, which is then inherited by their children. These retroviruses, known as endogenous retroviruses, are present in the genome of all mammals, including humans. Consequently, endogenous retroviruses can be considered remnants of ancient retroviral infections, Spencer said.

Many scientists believed these endogenous retroviruses were junk DNA, he said.

“Indeed, these endogenous retroviruses are usually harmless and generally contain mutations that prevent them from producing infectious retroviruses,” he said.

However, several endogenous retroviruses appear to provide protection from infection and are involved in reproduction. For instance, the exogenous Jaagsiekte Sheep Retrovirus or JSRV causes lung tumors in sheep and led to the death of Dolly, the world’s first mammal cloned from an adult cell. The idea that endogenous retroviruses are important for reproduction in mammals has been around for about 30 years, Spencer said. Studies in cultured cells have shown that a protein of a human endogenous retrovirus might have a role in development of the human placenta. - Here

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The life of a cell is all about growing and dividing at the right time. That is why the cell cycle is one of the most tightly regulated cellular processes. A control system with several layers adjusts when key components of the cell cycle machinery are produced, activated and degraded to make sure that the schedule is kept. These layers of control work differently and are usually studied separately, but researchers at the European Molecular Biology Laboratory (EMBL) and the Technical University of Denmark (DTU) have now discovered that they change in a highly coordinated fashion during evolution. The study, which will be published in this week’s online issue of Nature, also reveals that although most components of the cell cycle have been conserved over one billion years, the temporal regulation of this process has evolved remarkably fast. - Here