effective silencing suppressor essential for infection – Savvy Essay Writers | savvyessaywriters.net
effective silencing suppressor essential for infection – Savvy Essay Writers | savvyessaywriters.net
sophila cells with an RNA virus triggers strong virus RNA silencing and that the same virus is equipped with an effective silencing suppressor essential for infection. These data provide direct evidence that RNA silencing naturally acts as an adaptive antiviral defense in animal cells. The specificity mechanism of this adaptive defense is based on nucleic acid base pairing between siRNA and its target RNA (1, 2) and thus is distinct from cellular and humoral adaptive im- munity based on peptide recognition (19). A prediction from our work is that heterologous sequences inserted into a replicating virus genome will lead to the production of a pop- ulation of siRNAs capable of silencing other viral and cellular RNAs in trans that are ho- mologous to the insert. Indeed, recent studies showed that viral sequences inserted in alpha- virus vectors give rise to virus resistance in mosquitoes, which is dependent on the insert- ed RNA sequence rather than on its protein product (20, 21). It will be of interest to determine if RNA silencing also plays a role in observed protection against mammalian vi- ruses, derived similarly from heterologous ex- pression of RNA sequences from a replicating RNA virus vector (22).
References and Notes 1. D. Baulcombe, Curr. Biol. 12, R83 (2002). 2. G. Hutvagner, P. D. Zamore, Curr. Opin. Genet. Dev.
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(2001). 5. S. W. Ding, W. X. Li, R. H. Symons, EMBO J. 14, 5762
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157 (2000). 9. H. S. Guo, S. W. Ding, EMBO J. 21, 398 (2002).
10. A. J. Hamilton, D. C. Baulcombe, Science 286, 950 (1999).
11. S. W. Ding, B. J. Shi, W. X. Li, R. H. Symons, Proc. Natl. Acad. Sci. U.S.A. 93, 7470 (1996).
12. R. Dasgupta, B. H. Garcia, R. M. Goodman, Proc. Natl. Acad. Sci. U.S.A. 98, 4910 (2001).
13. L. A. Ball et al., in Virus Taxonomy–Seventh Report of the International Committee on Taxonomy of Viruses, M. H. V. van Regenmortel et al., Eds. (Academic Press, San Diego, CA, 2000), pp. 747–755.
14. K. L. Johnson, L. A. Ball, J. Virol. 73, 7933 (1999). 15. L. A. Ball, J. Virol. 69, 720 (1995). 16. S. M. Hammond, S. Boettcher, A. A. Caudy, R. Koba-
yashi, G. J. Hannon, Science 293, 1146 (2001). 17. E. Bernstein, A. A. Caudy, S. M. Hammond, G. J.
Hannon, Nature 409, 363 (2001). 18. S. M. Elbashir et al., Nature 411, 494 (2001). 19. J. L. Whitton, M. B. A. Oldstone, in Fields Virology,
D. M. Knipe, P. M. Howley, Eds. (Lippincott Williams & Wilkins, Philadelphia, PA, vol. 1, chap. 11. [fourth edition].
20. A. Billecocq, M. Vazeille-Falcoz, F. Rodhain, M. Bouloy, J. Gen. Virol. 81, 2161 (2000).
21. Z. N. Adelman, C. D. Blair, J. O. Carlson, B. J. Beaty, K. E. Olson, Insect Mol. Biol. 10, 265 (2001).
22. N. F. Rose et al., Cell 106, 539 (2001). 23. S. M. Hammond, E. Bernstein, D. Beach, G. J. Hannon,
Nature 404, 293 (2000). 24. We thank G. Hannon for providing RNAi reagents
and in-house training (to H.L.); D. Baulcombe and K. Gordon for materials; A. Gibbs and S. Wong for discussions; and D. Carter and J. Brimo (www.
cepceb.ucr.edu) for their assistance in preparing the GFP images. Supported by a Faculty Start-up fund from the University of California-Riverside (S.D.) and a grant from the U.S. Department of Agriculture National Research Initiative Competi- tive Grants Program (S.D.).
Supporting Online Material (www.sciencemag.org/cgi/content/full/296/5571/1319/DC1) Materials and Methods fig. S1
15 February 2002; accepted 12 April 2002
Is Face Processing Species-Specific During the First
Year of Life? Olivier Pascalis,1* Michelle de Haan,2 Charles A. Nelson3
Between 6 and 10 months of age, the infant’s ability to discriminate among native speech sounds improves, whereas the same ability to discriminate among foreign speech sounds decreases. Our study aimed to determine whether this perceptual narrowing is unique to language or might also apply to face processing. We tested discrimination of human and monkey faces by 6-month-olds, 9-month-olds, and adults, using the visual paired-comparison procedure. Only the youngest group showed discrimination between individuals of both species; older infants and adults only showed evidence of discrimination of their own species. These results suggest that the “perceptual narrowing” phenomenon may represent a more general change in neural networks involved in early cognition.
At first glance the development of the ability to recognize faces appears to follow a typical tra- jectory: rapid change during infancy, followed by more gradual improvement into adolescence (1). This pattern contrasts with some aspects of language development. For example, speech perception is characterized by a loss of ability with age, such that 4- to 6-month-olds can dis- criminate phonetic differences that distinguish syllables in both their native and unfamiliar languages, whereas 10- to 12-month-olds can only discriminate the phonetic variations used in their native language (2, 3). Here we describe a similar phenomenon for face recognition: Spe- cifically, we demonstrate that 6-month-old in- fants are equally good at recognizing facial identity in both human and nonhuman primates, whereas 9-month-old infants and adults show a marked advantage for recognizing only human faces.
Nelson (4) has proposed that the ability to perceive faces narrows with development, due in large measure to the cortical specialization that occurs with experience viewing faces. In this view, the sensitivity of the face recognition system to differences in identity among the fac- es of one’s own species will increase with age and with experience in processing those faces. By adulthood the extensive experience with hu-
man faces can be mentally represented as a prototype that is “tuned” to the face inputs most frequently observed (human faces), with indi- vidual faces encoded in terms of how they de- viate from the prototype (5). Because infants begin to show evidence of forming face proto- types by 3 months of age (6), their face recog- nition should become more “human face specif- ic” some time after this. This leads to the pre- diction that younger infants, who possess less experience with faces than older infants and adults, should be better than older infants or adults at discriminating between individual fac- es of other species.
This hypothesis is indirectly supported by several lines of research. For example, human adults are far more accurate in recognizing in- dividual human than monkey faces; the opposite is true for monkeys (7). Such species-specificity may be due to the differential expertise in the two groups: monkeys are more familiar with monkey than human faces, whereas humans are more familiar with human than monkey faces. Human infants, of course, likely have no expe- rience with monkey faces and relatively little experience with human faces. This may confer upon them a more broadly tuned face recogni- tion system and, in turn, an advantage in recog- nizing facial identity in general (i.e., regardless of species). This prediction is supported by a preliminary study (8) in which it was demon- strated using event-related potentials (ERPs) that young infants, but not adults, could discrim- inate monkey face identity across changes in facial orientation. A second ERP study exam- ined the influence of stimulus inversion, a ma- nipulation that in behavioral studies impairs adults’ recognition of identity of human faces
1Department of Psychology, The University of Shef- field, Sheffield S10 2TP, UK. 2Institute of Child Health, Developmental Cognitive Neuroscience Unit, Univer- sity College London, London WC1N 2AP UK. 3Insti- tute of Child Development, Department of Pediatrics, and Center for Neurobehavioral Development, Uni- versity of Minnesota, Minneapolis, MN 55455, USA.
*To whom correspondence should be addressed. E- mail: o.pascalis@sheffield.ac.uk
R E P O R T S
www.sciencemag.org SCIENCE VOL 296 17 MAY 2002 1321
more than objects (9). In adults, inversion af- fected only the processing of human faces and not monkey faces, whereas in 6-month-olds, inversion affected the ERPs similarly for human and monkey faces (10). This suggests that in- fants were processing facial identity in the two species comparably. It is noteworthy that this was not because they failed to detect the differ- ence between the two species, as the early- latency sensory components of the ERP differed for human and monkey faces for both ages. None of these studies directly tested the discrim- ination abilities of older and younger infants and adults in the same experimental procedure. We compared the ability of 6- and 9-month-old infants and adults to process human and monkey faces with the same visual paired-comparison procedure. We hypothesized that if face recog- nition follows the same developmental pattern as language, the ability to process other species’ faces will be present only in the youngest age group studied. A similar development (tuning period) for face recognition and for language may indicate a more general sensitive or tuning period for various cognitive functions. A visual paired-comparison procedure (VPC) was used to assess recognition in both infants and adults. VPC indexes the relative interest in the mem- bers of a pair of visual stimuli made of one novel item and one item already seen in a prior familiarization period. Recognition is inferred from the participant’s tendency to fixate the
novel stimulus significantly longer. The stimuli were colored pictures (Fig. 1) of human Cauca- sian (male and female faces from our collection) and monkey faces (Macaca fascicularis) [details of materials and methods (11)].
Eleven adult participants with no special ex- pertise in monkey face recognition were tested (11). For human…
