Model Organisms in Drug Discovery

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164 MECHANISM OF ACTION IN MODEL ORGANISMS Figure 6.2 Compound BMS AG6B induces Notch-like phenotypes in Drosophila. Adult flies and their progeny were treated with 10 mM BMS AG6B. Micrographs show the representative control (DMSO)-treated (A, C, E, G) and BMS AG6B-treated (B, D, F, H) adult progeny: (A, B). The normally smooth wing margin is notched in B (indicated by an arrow); (C, D) ‘Rough eye’ phenotype is shown in D; (E, F) E shows a morphologically wild-type leg and in F the tarsal segment is missing or fused; (G, H) the wild-type abdomen shown in G is covered with dark bristles and an area in H lacking bristles after drug treatment is circled
A CASE STUDY FOR ALZHEIMER’S DISEASE DRUG DISCOVERY 165 developed to adulthood. However, some treated worms were egg-laying defective (Egl-d), as demonstrated by the presence of late-stage eggs in the uterus, which give the animals a bloated appearance that is apparent at low magnification. The phenotype was found to be dose dependent (Figure 6.3D). There are many tissues and signaling pathways required for normal egglaying in C. elegans, and the drug-induced phenotypes could potentially signify a disruption in any one or more of them. The observation that larval treatment was required for the effect suggested a developmental rather than a neuromuscular defect. When drug-treated worms were examined in late larval stages by high magnification for morphological or positional changes in important egg-laying tissues – vulva, somatic gonad, sex muscles and hermaphrodite-specific neuron – all of the structures appeared quite normal. However, close examination revealed that some of the treated animals harbored dead embryos (Figures 6.3A and 6.3B). Interestingly, some embryos were found to lack an anterior pharynx, known as an Aph phenotype (Figure 6.3C). This morphological signature also pointed to the Notch pathway. There are two Notch receptors in worms – lin-12 and glp-1 – that mediate many cell-fate decisions (Austin and Kimble, 1989; Yochem and Greenwald, 1989; Kimble and Simpson, 1997). Notch receptor glp-1 is required for germline proliferation and embryonic development, particularly the signaling event that gives rise to the anterior pharyngeal lineage. Strong loss-of-function glp-1 mutants are sterile and weaker alleles are maternal-effect embryonic lethal, giving rise to Aph (anterior pharynx missing) progeny. Notch receptor lin-12 is required for many post-embryonic cell-fate decisions. lin-12 null alleles are sterile and weaker alleles are Egl-d due to defects in the vulval precursor cells and sex muscles. The two Notch proteins together control zygotic viability because lin-12; glp-1 double mutants die as larvae (Lambie and Kimble, 1991). Overall, the drug treatment phenotypes were consistent with decreased, if not eliminated, Notch activity in worms, although the phenotypic match was not exact. For example, BMS AG6B-treated worms had normal vulval induction and a single anchor cell (data not shown). Because mutations in the pathway or target might be expected to enhance or suppress the phenotype, the compound was tested on a panel of mutants in the Notch pathway. To test the hypothesis that the drug could be decreasing Notch activity, worms carrying an activated Notch allele lin-12(n137) were treated with BMS AG6B. This lin-12 mutant carries a missense mutation in the extracellular domain of the protein that acts to increase lin-12 signaling (resulting in extra vulval structures) and is known as a Muv phenotype (Greenwald and Seydoux, 1990). The number and frequency of these extra vulval structures were significantly reduced in worms treated with BMS AG6B (Table 6.2). The simplest explanation for the results are that BMS AG6B inhibits Notch protein function directly, inhibits a positive regulator of Notch signaling or activates a negative regulator.
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Model Organisms in Drug Discovery M
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Copyright u 2003 John Wiley & Sons
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Contents List of contributors .....
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CONTENTS ix 7 Genetics and Genomics
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List of Contributors Hector Beltran
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LIST OF CONTRIBUTORS xiii Stefan Sc
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1 Introduction to Model Systems in
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Organism INTEGRATING MODEL ORGANISM
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INTEGRATING MODEL ORGANISM RESEARCH
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INTEGRATING MODEL ORGANISM RESEARCH
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10 GROWING YEAST FOR FUN AND PROFIT
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3 Caenorhabditis elegans Functional
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THE DRUG DISCOVERY PROCESS 43 thoug
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multivulva phenotype of Ras gain-of
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disease. These molecular targets ar
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FROM DISEASE TO TARGET 49 Figure 3.
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FROM DISEASE TO TARGET 51 Figure 3.
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signaling pathway. The third catego
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FROM DISEASE TO TARGET 55 resistant
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phenomenon was first observed in C.
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profiles. The C. elegans gene expre
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emerging technologies. Forward gene
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The compound library LEAD DISCOVERY
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LEAD DISCOVERY 65 previous section,
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LEAD DISCOVERY 67 Figure 3.5 Distri
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Compound learning set for assay val
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10 000-15 000 human drug targets ar
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transporter itself. The SSRIs that
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REFERENCES 75 de Montigny, C., Blie
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REFERENCES 77 Lewis, J. A., Wu, C.
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REFERENCES 79 Tissenbaum, H. A. and
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82 DROSOPHILA AS A TOOL FOR DRUG DI
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100 DROSOPHILA AS A TOOL FOR DRUG D
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Page 121 and 122: 112 DROSOPHILA AS A TOOL FOR DRUG D
Page 127 and 128: 5 Drosophila - a Model System for T
Page 129 and 130: EVOLUTIONARY CONSERVATION OF DISEAS
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Page 151 and 152: CHEMICAL GENETICS 143 acid identity
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Page 155 and 156: about their function in a multicell
Page 157 and 158: REFERENCES 149 Han, Z. S., Enslen,
Page 159 and 160: REFERENCES 151 Rintelen, F., Stocke
Page 161 and 162: 6 Mechanism of Action in Model Orga
Page 163 and 164: INTRODUCTION TO COMPOUND DEVELOPMEN
Page 165 and 166: MODEL ORGANISMS ARRIVE ON THE SCENE
Page 167 and 168: ELUCIDATING THE MECHANISM OF COMPOU
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Page 171: A CASE STUDY FOR ALZHEIMER’S DISE
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Page 179 and 180: NEW CHEMICAL GENETIC STRATEGIES 171
Page 181 and 182: A CASE STUDY FOR INNATE IMMUNITY 17
Page 183 and 184: GLOBAL GENE EXPRESSION STUDIES IN M
Page 185 and 186: As described above, the extensive i
Page 187 and 188: REFERENCES 179 Austin, J. and Kimbl
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Page 191 and 192: REFERENCES 183 Sin, N., Meng, L., W
Page 193 and 194: 186 GENETICS AND GENOMICS IN THE ZE
Page 209 and 210: 8 Lipid Metabolism and Signaling in
Page 211 and 212: FISH AS A MODEL ORGANISM 205 genes
Page 213 and 214: LIPID METABOLISM SCREEN 207 transpo
Page 215 and 216: LIPID METABOLISM SCREEN 209 Figure
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Page 219 and 220: ZEBRAFISH AS A MODEL SYSTEM 213 Fig
Page 221 and 222: ZEBRAFISH AS A MODEL SYSTEM 215 Reg
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aspirin, which has potent inhibitor
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REFERENCES 219 Chau, I. and Cunning
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REFERENCES 221 Patrono, C., Patrign
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224 CHEMICAL MUTAGENESIS IN THE MOU
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252 SATURATION SCREENING OF DRUGGAB
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280 INDEX bupropion 92 busulfan 143
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282 INDEX Dscam 171 dual-energy X-r
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284 INDEX L-685,818 16 lead discove
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286 INDEX protein function 19-22 pr
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288 INDEX yeast (continued) functio
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