The retrotransposon - derived capsid genes PNMA1 and PNMA4 maintain reproductive capacity.

The human genome contains 24 gag -like capsid genes derived from deactivated retrotransposons conserved among eutherians. Although some of their encoded proteins retain the ability to form capsids and even transfer cargo, their fitness benefit has remained elusive. Here we show that the gag -like genes PNMA1 and PNMA4 support reproductive capacity. Six-week-old mice lacking either Pnma1 or Pnma4 are indistinguishable from wild-type littermates, but by six months the mutant mice become prematurely subfertile, with precipitous drops in sex hormone levels, gonadal atrophy, and abdominal obesity; overall they produce markedly fewer offspring than controls. Analysis of donated human ovaries shows that expression of both genes declines normally with aging, while several PNMA1 and PNMA4 variants identified in genome-wide association studies are causally associated with low testosterone, altered puberty onset, or obesity. These findings expand our understanding of factors that maintain human reproductive health and lend insight into the domestication of retrotransposon-derived genes.

Evolution and antiviral activity of a human protein of retroviral origin.

Endogenous retroviruses are abundant components of mammalian genomes descended from ancient germline infections. In several mammals, the envelope proteins encoded by these elements protect against exogenous viruses, but this activity has not been documented with endogenously expressed envelopes in humans. We report that the human genome harbors a large pool of envelope-derived sequences with the potential to restrict retroviral infection. To test this, we characterized an envelope-derived protein, Suppressyn. We found that Suppressyn is expressed in human preimplantation embryos and developing placenta using its ancestral retroviral promoter. Cell culture assays showed that Suppressyn, and its hominoid orthologs, could restrict infection by extant mammalian type D retroviruses. Our data support a generalizable model of retroviral envelope co-option for host immunity and genome defense.

Structures of virus-like capsids formed by the Drosophila neuronal Arc proteins.

Arc, a neuronal gene that is critical for synaptic plasticity, originated through the domestication of retrotransposon Gag genes and mediates intercellular messenger RNA transfer. We report high-resolution structures of retrovirus-like capsids formed by Drosophila dArc1 and dArc2 that have surface spikes and putative internal RNA-binding domains. These data demonstrate that virus-like capsid-forming properties of Arc are evolutionarily conserved and provide a structural basis for understanding their function in intercellular communication.