This Week in Science

Science  14 Jun 1996:
Vol. 272, Issue 5268, pp. 1561
  1. A patched path to cancer

    Little has been known about the genes involved in the pathogenesis of basal cell carcinoma (BCC), the most common human cancer. The majority of BCCs develop sporadically during middle age, but patients with an inherited disorder called basal cell nevus syndrome (BCNS) develop BCCs at high frequency at an early age. Johnson et al. (p. 1668; see the news story by Pennisi, (p. 1583) identified the gene responsible for BCNS—and most likely for a subset of sporadic BCCs—as the human homolog of the gene patched. In fruit flies, patched codes for a transmembrane protein that down-regulates expression of certain growth factor genes and that is required for normal pattern formation during development. Patients with BCNS also suffer from a variety of developmental abnormalities, suggesting that the role of patched is evolutionarily conserved.

  2. Went their own way

    When climate change affects an ecosystem, do biological ties within a community prevail over this external pressure on the system? Graham et al. (p. 1601) used a large database from the United States to address these questions by examining the response of mammals to the warming since the last glaciation. During periods of a few thousand years, ranges of species shifted in different directions and at different rates. Thus coherent mammalian ecosystems were not maintained

  3. Neatly folded


    Proteins may unfold or fold improperly in cells under stress. Molecular chaperones of the 70-kilodalton heat-shock protein (hsp70) family assist folding by binding to the aggregation-prone protein segments that become unsuitably exposed. Zhu et al. (p. 1606) describe crystal structures of the substrate-binding unit from DnaK, the bacterial hsp70, in a complex with a peptide substrate. The peptide is encapsulated in a channel through DnaK, and it appears that an adenosine triphosphate-driven change of conformation promotes the substrate exchange required to control proper folding.

  4. The A list

    In Drosophila, the appendages develop from imaginal discs, which are composed of two distinct cell populations known as the anterior (A) and posterior (P) compartments. Cells in the P compartment express engrailed (en), which is necessary for establishing P cell identity. Domínguez et al. (p. 1621) found that A cell identity is not determined simply by a lack of en expression but also requires the expression of the zinc finger protein Cubitus interruptus (Ci). Because ci loss-of-function mutations are embryonic lethal, they studied the role of Ci in genetic mosaics.

    Expression of Ci in A cells is required to limit the expression of the signaling molecule Hedgehog (Hh) to cells of the P compartment and that ci confers competence to respond to Hh by activating decapentaplegic expression. Thus ci plays a role in establishing the AP boundary.

  5. Cool molecules

    Vibrational and rotational spectra of complex molecules are made even more complex by the population of numerous excited states. Cooling the molecules can simplify the spectra by bringing the levels near the ground states. Hartmann et al. (p. 1631) have isolated molecules and small molecular clusters in ultracold liquid helium droplets, and resolved their vibrational and rotational structure. Superfluidity of the helium droplets is indicated by the quasi-freerotation of the nonspherical clusters within the droplets.

  6. Supercritical pH

    Measuring properties of supercritical fluids has been difficult in both geology and engineering. Ding and Seyfried (p. 1634) now describe and apply an in situ pH sensor for supercritical fluids in experiments. Their electrochemical cell contains a yttrium-doped zirconia membrane and Ag/AgCl reference electrode. Measurements of the pH of NaCl-HCl bearing fluids at 400°C and 4 megapascals shows good agreement with theoretical predictions.

  7. Worth repairing

    When damage to a cellular DNA is catastrophic, the best response may be apoptosis or death to that particular cell, but what if the DNA damage is something less than catastrophic but perhaps unrepairable? Oda et al. (p 1644) found that replication of DNA molecules with even minimal damage is arrested in some eukaryotic cells. This arrest can be bypassed by certain prokaryotic mutagenesis proteins. Some eukaryotic cell types may have a similar system to bypass a limited number of unrepairable DNA lesions.

  8. Losing inhibitions

    The yeast Gal4p protein is a key regulator of galactose metabolism. Gal4p activity is inhibited by Gal80p. This inhibition is relieved in the presence of galactose, but the mechanism has been unclear. Zenke et al. (p. 1662) found that galactokinase, the first enzyme of galactose metabolism, interacts with the inhibitor Gal80p in the presence of galactose to form a Gal80p-Gal1p complex, which prevents Gal80p from inhi biting Gal4p.

  9. About face

    The visual system executes a complex parsing of our visual world into features that then are recombined into shapes andobjects and colors, leading to perception. Neurons with similar response properties are usually grouped in columns perpendicular to the surface of the cerebral cortex. Wang et al. (p1665) used optical imaging and unit recordings to find a similarorganization of cells in the monkey inferotemporal cortex, one of the late stages of the visual pathway that is specialized for object recognition. In a series of presentations of faces, rotated from a left-profile to right, the location of active neurons shifted systematically within this cortical region.

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