This Week in Science

Science  26 Aug 2011:
Vol. 333, Issue 6046, pp. 1067
  1. Seeing Red Across Species


    The phenomenon of mimicry in butterflies has generated wide-spread interest among naturalists and evolutionary biologists, but a developmental and genetic understanding of the process requires the identification of the individual genes involved Reed et al. (p. 1137, published online 21 July; see the Perspective by Carroll) identified the optix gene as the major determinant of red color patterns in multiple Heliconius butterfly species by tying gene expression data to color-pattern variation. Furthermore, cis-regulatory variation is likely responsible for the diversity of red patterns across species. The optix gene encodes a transcription factor that is also associated with the butterfly visual system and may thus have been co-opted from a different ancestral function.

  2. Mature Mitochondria?

    Mitochondria are the essential source of metabolic energy for the cell. These organelles direct crossroads from which cells can move down a path that leads to cell death or to inflammatory damage to an organism. They are thus important factors of certain diseases and, more universally, of the aging process. Green et al. (p. 1109) review recent insights into mitochondrial function, their roles in the control of cell death and in chronic inflammation, and the role of autophagy or, more specifically, mitophagy in protecting cells from mitochondrial damage.

  3. Extraterrestrial Dust Collection

    The Japanese Hayabusa spacecraft returned to Earth on 13 June 2010 carrying within it a precious but invisible cargo—1534 particles of dust from the surface of the asteroid Itokawa, which the spacecraft visited in 2005. These particles, up to 180 micrometers in size, are the first material ever fetched from an asteroid and returned to Earth for laboratory analysis (see the Perspective by Krot; see the cover). Nakamura et al. (p. 1113) describe the mineralogy of the particles; Yurimoto et al. (p. 1116) report measurements of the oxygen isotopic composition of minerals in 28 dust grains; and Ebihara et al. (p. 1119) discuss trace-element data for one of the largest grains in the collection. These studies confirm that the material is indeed extraterrestrial in origin and is similar to material in stony meteorites of the LL type, thus establishing an unequivocal link between asteroids and meteorites. Previously, meteorites were thought to originate from asteroids, based on spectroscopic studies of asteroid surfaces. However, these surfaces suffer from the effects of space weathering, which modifies their spectral properties compared with those of meteorites. Noguchi et al. (p. 1121) show that 5 of the 10 particles analyzed show evidence of surface alteration related to their exposure to the space environment on the surface of Itokawa and conclude that the process is different from the one operating on the Moon's surface. The particles collected by Hayabusa sample the asteroid's regolith, the layer of unconsolidated material that covers rocky surfaces. Based on the texture and shapes of the particles and on noble gas analyses of three grains, Tsuchiyama et al. (p. 1125) and Nagao et al. (p. 1128) trace the history of Itokawa's regolith, the second extraterrestrial regolith to have been sampled after the Moon's.

  4. Zeolites Up Close


    In the preparation of microporous zeolitic materials for catalysis, the introduction of hierarchical porosity has been of great interest. Because pores have multiple-size scales, it should be possible to enhance catalytic activity by controlling dif fusion characteristics. Jiang et al. (p. 1131) developed a zeolitic topology in which this hierarchical porosity is a natural feature of the material through the use of organic and inorganic structure-directing agents. Zeolites vary widely in the size and arrangement of their pore structures, but their lattice geometries can generally be described by a relatively simple replicated core arrangement. Baerlocher et al. (p. 1134) used sophisticated analysis of x-ray diffraction data to uncover the structure of an unexpectedly complex zeolite variant, in which the unit cell comprises 99 silicon atoms (compared with ∼20 or fewer observed in conventional zeolites).

  5. Getting There Is Only Half the Fun

    Although most transcription factors are synthesized in the same cell in which they act, in plants some transcription factors get shipped into other cells, where they take action on the genes of the destination cell. The transcription factors KNOTTED1 (KN1) of maize and the closely similar SHOOTMERISTEMLESS (STM) of Arabidopsis, as well as SHORTROOT (SHR) of Arabidopsis, are a few of these peripatetic regulators. These factors need to travel through the plasmodesmata that connect one cell to another. Xu et al. (p. 1141; see the Perspective by Jorgensen) used a reporter system in Arabidopsis that depends on the transport of the transcription factor to direct trichome development. A specific chaperonin complex was required in the recipient cell for full function of KN1 or STM, which highlights the need for refolding of these transcription factors after transport.

  6. Playing Checkers

    Developmental patterning is very important in the arrangements of cells within organs and tissues. The organ of Corti in the inner ear contains mechanosensory hair cells that are interdigitated with nonsensory supporting cells. During development, these two cell types are arranged in a checkerboard-like pattern. Togashi et al. worked in mice (p. 1144, published online 28 July; see the Perspective by Choi and Peifer) to show that the immunoglobulin-like cell-cell adhesion molecules nectin-1 and nectin-3 play a key role in this checkerboard-like patterning through their heterophilic interactions. Mice lacking either nectin-1 or -3 fail to organize their auditory epithelia properly. Thus, differential cell adhesion can control the spatial pattern of cells in a tissue.

  7. Little Fish, Big Fish

    Low–trophic level species in marine ecosystems are responsible for transmitting energy from primary producing phytoplankton to higher trophic levels. These species are also heavily harvested and make up 30% of global fisheries' production. Smith et al. (p. 1147, published online 21 July) used ecosystem models to explore the impacts that an increased harvest of low–tropic level species could have on marine ecosystems across the globe. Fishing these species at levels considered to be the maximum for sustaining the species can have large impacts on other ecosystem members (including fish, seabirds, and marine mammals). Halving exploitation rates has the potential to provide an adequate allocation for human use and to greatly reduce the ecosystem impacts of harvesting these essential species.

  8. Protein Phosphorylation by Design


    O-phosphoserine (Sep), the most abundant phosphoamino acid, is not genetically encoded but synthesized posttranslationally by a complex network of kinases and phosphatases. Park et al. (p. 1151) engineered an Escherichia coli strain that was able to incorporate Sep directly into proteins. The strain harbors a Sep-accepting transfer RNA (tRNASep), its cognate Sep–tRNA synthetase, and an elongation factor–Tu engineered to permit Sep-tRNASep binding. The system was used to synthesize a human kinase with one or two Sep residues inserted at specific sites. The ability to biosynthesize specific phosphoproteins directly will be very helpful for detailed studies of their enzyme and substrate properties.

  9. The Downside of Diversity

    Head and neck squamous cell carcinoma (HNSCC) affects about 600,000 individuals each year and has a mortality rate of about 50%. Environmental factors such as tobacco and alcohol use and human papillomavirus (HPV) infection are key participants in pathogenesis (see the Perspective by Brakenhoff). In independent studies aimed at exploring the molecular genetics of these tumors, Agrawal et al. (p. 1154, published online 28 July) and Stransky et al. (p. 1157, published online 28 July) sequenced the protein-coding genes of multiple tumors. Tumors from smokers had more mutations than those from nonsmokers, and tumors that were HPV-positive had fewer mutations than HPV-negative tumors. HNSCCs harbored mutations in a diverse array of genes, including genes implicated in squamous differentiation such as NOTCH1. Notably, the pattern of NOTCH1 mutations suggests that this gene acts as a tumor suppressor in HNSCC, in direct contrast to its role as an oncogene in other tumor types. The diverse mutational etiology of HNSCC and the dearth of activating mutations in established oncogenes suggest that targeted therapies for the disease will be especially challenging, which emphasizes the importance of prevention and early detection.

  10. Mediator Missense

    The Mediator complex is a multiprotein complex that functions as a transcriptional coactivator. Missense mutations in the Mediator complex can alter its activity as a regulator of gene transcription without eliminating such interactions. Hashimoto et al. (p. 1161) identified an alteration in the MED23 gene that encodes one of the Mediator subunits, which correlates with inherited intellectual disability in the affected family. The mutated MED23 protein causes altered regulation of the JUN and FOS genes, which have been linked to neuronal function, thus building a chain of events from transcriptional dysregulation to intellectual disability.