Designing gene drives to limit spillover to non-target populations

The prospect of utilizing CRISPR-based gene-drive technology for controlling populations has generated much excitement. However, the potential for spillovers of gene-drive alleles from the target population to non-target populations has raised concerns. Here, using mathematical models, we investigate the possibility of limiting spillovers to non-target populations by designing differential-targeting gene drives, in which the expected equilibrium gene-drive allele frequencies are high in the target population but low in the non-target population. We find that achieving differential targeting is possible with certain configurations of gene-drive parameters, but, in most cases, only under relatively low migration rates between populations. Under high migration, differential targeting is possible only in a narrow region of the parameter space. Because fixation of the gene drive in the non-target population could severely disrupt ecosystems, we outline possible ways to avoid this outcome. We apply our model to two potential applications of gene drives—field trials for malaria-vector gene drives and control of invasive species on islands. We discuss theoretical predictions of key requirements for differential targeting and their practical implications.     

The petunia homologue of tomato gast1: transcript accumulation coincides with gibberellin-induced corolla cell elongation

Gibberellins (GAs) regulate petunia corolla pigmentation and elongation. To study this hormone's effect at the molecular level, we used the tomato gast1 gene as a probe to isolate a gibberellin-induced gene (gip) from petunia corollas. The deduced sequence of gip exhibited 82% identity with GAST1 protein and contained a short, highly hydrophobic N-terminal region. High levels of gip expression were detected in elongating corollas and young stem internodes. When detached corollas were grown in vitro in sucrose medium, gip expression was strongly induced by gibberellic acid (GA₃). GA₃-induced gip expression in corollas was inhibited by abscisic acid (ABA). The expression of the gene was also induced by GA₃ in detached young stem segments. Sucrose was not essential for GA-induced gip expression in corollas but enhanced its effect. In stems, on the other hand, sucrose inhibited the effect of the hormone. The results of the present work support the possible role of gip in GA-induced corolla and stem elongation.     

DO PHOTOPERIOD AND TEMPERATURE INFLUENCE THE MOLT CYCLE OF PHOCA VITULINA IN CAPTIVITY?

Photoperiod variations are the principal environmental signals entraining circannual activity in mammals, which is also believed to be influenced by changes in temperature and nutrition. Control of the molt in phocids has not been extensively studied with experimental manipulations of environmental factors, but substantial work indicates that photoperiod has a primary influence on mammalian breeding and furring mechanisms. Studies were under taken to reestablish the molt cycle in five harbor seals ( Phoca vitulina ) previously kept in an enclosed facility with a limited air/water temperature gradient and artificial photoperiod. The seals were exposed to an extended temperature gradient during the first period of study, and no molting was observed. The second period of study was characterized by a natural occurring photoperiod of 8 h 53 min light (L)/15 h 07 min dark (D) and a maximal 15 h 31 min L/8h 29 min D duration, and molting occurred in all individuals. These results suggest a prevalent influence of photoperiod variation on the harbor seal molt.