An hypothesis for selection of strains of potato leaf roll virus by passage through Physalis floridana

Symptomatically distinct isolates of potato leaf roll virus were transmitted from White Rose to Russet Burbank potato by aphids and by grafting, from White Rose potato toP. floridana by aphids, and fromP. floridana toP. floridana by aphids. Isolates from White Rose potato generally produced stable and characteristic secondary leaf roll symptoms (but not primary leaf roll symptoms) when transmitted to Russet Burbank potato but variable symptoms when transmitted toP. floridana. Isolates from two of the latter plants with moderate and severe symptoms generally incited stable and characteristic symptoms when transmitted to otherP. floridana plants. The stable symptoms produced by each of these isolates were not modified by infestingP. floridana plants with varying numbers of viruliferous aphids. The results obtained in this study corroborate previous evidence for the existence of strains of potato leaf roll virus. It is suggested that certain White Rose potato plants contained mixtures of leaf roll virus strains. Furthermore, it is postulated that these mixtures were at least partially separated by “natural” selection following transmission toP. floridana. This mechanism provides an explanation for the stable symptoms produced by isolates transmitted fromP. floridana toP. floridana.     

Human CHN1 mutations hyperactivate alpha2-chimaerin and cause Duane's retraction syndrome

Duane's retraction syndrome (DRS) is a complex congenital eye movement disorder caused by aberrant innervation of the extraocular muscles by axons of brainstem motor neurons. Studying families with a variant form of the disorder (DURS2-DRS), we have identified causative heterozygous missense mutations in CHN1, a gene on chromosome 2q31 that encodes alpha2-chimaerin, a Rac guanosine triphosphatase-activating protein (RacGAP) signaling protein previously implicated in the pathfinding of corticospinal axons in mice. We found that these are gain-of-function mutations that increase alpha2-chimaerin RacGAP activity in vitro. Several of the mutations appeared to enhance alpha2-chimaerin translocation to the cell membrane or enhance its ability to self-associate. Expression of mutant alpha2-chimaerin constructs in chick embryos resulted in failure of oculomotor axons to innervate their target extraocular muscles. We conclude that alpha2-chimaerin has a critical developmental function in ocular motor axon pathfinding.     

Spatial Response of Mammals to Late Quaternary Environmental Fluctuations

Analyses of fossil mammal faunas from 2945 localities in the United States demonstrate that the geographic ranges of individual species shifted at different times, in different directions, and at different rates in response to late Quaternary environmental fluctuations. The geographic pattern of faunal provinces was similar for the late Pleistocene and late Holocene, but differing environmental gradients resulted in dissimilar species composition for these biogeographic regions. Modern community patterns emerged only in the last few thousand years, and many late Pleistocene communities do not have modern analogs. Faunal heterogeneity was greater in the late Pleistocene.