In Science this week, researchers at the University of Washington School of Medicine and members of the 1,000 Genomes Project, along with their industry colleagues, report their analysis of the "diversity of human copy number variation and multi-copy genes." In their investigations of 159 human genomes, the team found more than 4 million "'singly unique nucleotide' positions informative in distinguishing specific copies," as well as "human-specific expansions in genes associated with brain development … extensive population diversity, and … signatures consistent with gene conversion in the human species," the authors write.
A team of investigators at Brown University shows that "prion conformations may specify phenotypes as population averages in a dynamic system." More specifically, using the yeast prion Sup35/[PSI+], Aaron Derdowski et al. determined that the protein's conformation governs the distribution of aggregates — though its interactions with a molecular chaperone — in a size-wise fashion. In this way, the authors write, "shifts in this range created variations in aggregate abundance among cells because of a size threshold for transmission, and this heterogeneity, along with aggregate growth and fragmentation, induced age-dependent fluctuations in phenotype."
In a review paper published in Science this week, Déborah Bourc'his at the Institut Curie in Paris and Olivier Voinnet at the Institut de Biologie Moléculaire des Plantes in Strasbourg, France, provide "a small RNA perspective on gametogenesis, fertilization, and early zygotic development." Both cis- and trans-acting small RNAs work to maintain genome integrity in the gametes and zygote and also "contribute to assessing the compatibility of parental genomes at fertilization and to promoting long-term memory of the zygotic epigenetic landscape by affecting chromatin," Bourc'his and Voinnet write, adding that "striking parallels exist in the biogenesis and modus operandi of these molecules among diverse taxa."
The University of Arizona's Vicki Chandler discusses how paramutation, though rare, "may underlie fundamental mechanisms for gene regulation" in this week's Science. Chandler addresses speculations on potential roles for paramutation — "the process by which homologous DNA sequences communicate in trans to establish meiotically heritable expression states" — as an adaptive mechanism, which passes on favorable expression states to progeny, establishes functional homozygosity in polyploids, and confers inbreeding depression and/or hybrid vigor. Whatever its function, Chandler suggests that researchers' understanding of paramutation "should shed light on potentially novel mechanisms for transmitting epigenetic information across generations."