Cantharidin production in a blister beetle

Cantharidin, a potent defensive chemical, is present in all ten life stages of the blister beetleEpicauta funebris. The first five larval stages accumulate cantharidin as they feed and grow in size. When disturbed, they exude cantharidin in a milky oral fluid, not in hemolymph which adult beetles reflexively discharge from leg joints. Two subsequent larval stages and the pupa do not feed, grow, regurgitate, or change in their defensive reserves (110 g cantharidin/insect, regardless of sex). Adult beetles kept in isolation for 60–90 d exhibit a pronounced sexual dimorphism in cantharidin production: the male biosynthesizes about 17 mg of the toxin, representing 10% of his live weight, whereas the female actually loses most of her defensive reserves. But in the wild a female beetle repeatedly acquires cantharidin as copulatory gifts from her mates.This study was supported by Grant DK 31186 and by the University of Missouri Institutional Biomedical Research Support Grant RR07053, both from the National Institutes of Health.     

Ecology of flannelmouth sucker in the Lee's Ferry tailwater, Colorado River, Arizona

We investigated ecology of flannelmouth sucker ( Catostomus latipinnis ) from 1992 to 1997 in the 26-km Lee's Ferry reach of the Colorado River immediately below Glen Canyon Dam, Arizona. We captured by electrofishing a total of 212 fish and recaptured 52 previously tagged by others. Flannelmouth sucker were captured throughout the tailwater but tended to aggregate about 5 km of the dam, possibly reflecting blockage of historic migration routes. Catch per hour of electrofishing did not differ among years but was greater from November to February than other periods, suggesting seasonal movements of flannelmouth sucker into the tailwater: Mean lengths and weights of fish did not differ among years or seasons. Length frequency analyses also indicated there were no significantly yearly trends in proportion of catch within size classes of fish. Mean condition differed only among seasons and was greatest in February, lowest in August, coinciding respectively with pre- and post-spawning periods of flannelmouth sucker in tributary just down from Lee's Ferry. Recaptured fish migrated from initial tagging locations 1.4-23.1 km downstream from Lee's Ferry. Fifty-nine percent of recaptured fish with known initial tagging locations increased in length, and fish tagged initially as subadults or adults, respectively, grew an average of 45.9 mm and 5.5 mm per year.     

Transient reversion of ras oncogene-induced cell transformation by antibodies specific for amino acid 12 of ras protein

The proteins encoded by the ras oncogene are thought to trigger expression of the transformed phenotype in some types of cancer cells. In human cells, the ras protein family consists of several members including normal (proto-oncogene) and mutant (oncogene) forms. In general, the proto-oncogene forms are thought to be involved in the normal growth control of cells, while the mutant forms (which apparently result from somatic mutation of the normal ras genes) appear to be responsible, in part, for the loss of normal growth control. On microinjection into living normal cells, the purified ras oncogene protein (p21) induces a characteristic loss of growth control in cells within several hours. The mutant forms of the different ras proteins typically contain a single amino-acid change, usually at position 12 or less frequently at position 61. Here we report that microinjection of antibodies specific for amino acid 12 of the oncogenic v-Ki-ras protein into cells transformed by this protein causes a transient reversion of the cells to a normal phenotype. The fact that this antibody inhibits binding of GTP to the v-Ki-ras protein supports the notion that GTP binding is essential to the transforming function of this oncogene product.     

Charge-transfer complexations among biochemically reactive compounds

Zusammenfassung Bei vielen biochemischen Stoffen wird die mit Ladungstransfer verbundene Komplexbildung durch Veränderungen im gemessenen Absorptionsspektrum angezeigt. Die mögliche Bedeutung einer solchen Komplexbildung, insbesondere bei Wasserstoff-und Elektronentransport innerhalb biologischer Systeme, wird diskutiert.

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This work was supported by Public Health Service Grants HE-04138 and AM-04585.     

Differential regulation of rasGAP and neurofibromatosis gene product activities

The ras-encoded p21ras proteins bind GTP very tightly, but catalyse hydrolysis to GDP very slowly. In humans, two genes encode proteins that stimulate this GTPase activity (GAP, or GTPase-activating proteins), one of relative molecular mass 120,000, referred to as p120-GAP, and another NF1-GAP, which is encoded by the neurofibromatosis type-1 gene. Both GAPs are widely expressed in mammalian tissues. Here we show that although they will both bind oncogenic mutants of p21ras, neither will stimulate their GTPase activity. NF1-GAP binds to the p21ras proteins up to 300 times more efficiently than p120-GAP. The two GAPs are inhibited to different extents by certain lipids: micromolar concentrations of arachidonate, phosphatidate and phosphatidylinositol-4,5-bisphosphate affect only NF1-GAP. This inhibition does not compete with p21ras, and lipid-inactivated NF1-GAP can still bind p21ras. We used the detergent dodecyl maltoside, which inhibits only NF1-GAP, to distinguish between the two activities in cell extracts and found both types present together in several mammalian cell lines. In contrast, GAP activity in extracts of Xenopus oocytes was not affected by dodecyl maltoside. By these criteria, the mammalian cells contain both GAP activities and the oocytes have only p120-like GAP activity. These results indicate that more than one GAP regulates p21ras in the same cell.     

Acetylcholine induces burst firing in thalamic reticular neurones by activating a potassium conductance

Recent studies have emphasized the role of acetylcholine (ACh) as an excitatory modulator of neuronal activity in mammalian cortex and hippocampus. Much less is known about the mechanism of direct cholinergic inhibition in the central nervous system or its role in regulating neuronal activities. Here we report that application of ACh to thalamic nucleus reticularis (nRt) neurones, which are known to receive a cholinergic input from the ascending reticular system of the brain stem, causes a hyperpolarization due to a relatively small (1-4 nS) increase in membrane conductance to K+. This cholinergic action appears to be mediated by the M2 subclass of muscarinic receptors and acts in conjunction with the intrinsic membrane properties of nucleus reticularis neurones to inhibit single spike activity while promoting the occurrence of burst discharges. Thus, cholinergic inhibitory mechanisms may be important in controlling the firing pattern of this important group of thalamic neurones.     

Recruitment of entomopathogenic nematodes by insect-damaged maize roots

Plants under attack by arthropod herbivores often emit volatile compounds from their leaves that attract natural enemies of the herbivores. Here we report the first identification of an insect-induced belowground plant signal, (E)-beta-caryophyllene, which strongly attracts an entomopathogenic nematode. Maize roots release this sesquiterpene in response to feeding by larvae of the beetle Diabrotica virgifera virgifera, a maize pest that is currently invading Europe. Most North American maize lines do not release (E)-beta-caryophyllene, whereas European lines and the wild maize ancestor, teosinte, readily do so in response to D. v. virgifera attack. This difference was consistent with striking differences in the attractiveness of representative lines in the laboratory. Field experiments showed a fivefold higher nematode infection rate of D. v. virgifera larvae on a maize variety that produces the signal than on a variety that does not, whereas spiking the soil near the latter variety with authentic (E)-beta-caryophyllene decreased the emergence of adult D. v. virgifera to less than half. North American maize lines must have lost the signal during the breeding process. Development of new varieties that release the attractant in adequate amounts should help enhance the efficacy of nematodes as biological control agents against root pests like D. v. virgifera.