Loss of the gene X product reverses the mutant phenotype. To determine whether suppression is specific for a particular cellular process or is due to a fairly direct interaction with lin-35 target genes, Polley and Fay measured the degree of suppression of six other lin-35 synthetic phenotypes, for example, defects in gonad or germline development or defects in pharynx development. Copyright © 2020 by the Genetics Society of America, Department of Biology, Lawrence University, Appleton, Wisconsin 54911. This process repeats through L3 and L4 larval stages until the worm becomes an adult capable of reproduction. Resveratrol, an indirect SIRT1 activator, enhances mutant PABPN1 toxicity whereas EX-527, a selective SIRT1 inhibitor, has the opposite effect (Catoire et al., 2008; Pasco et al., 2010). Using the light circuit metaphor again, non-additive suppressors each might remove the same light switch bracket while additive suppressors might remove brackets controlling different lights. Polley and Fay use a synthetic phenotype, an unusual and sometimes difficult concept. Tissue-specific transcription factors may also recruit proteins that alter chromatin structure, thereby making the promoter and enhancer more or less accessible to other transcription factors. This device has high depth of field (40 µm at resolution of 7.4 µm; 8 µm at resolution of 1 µm), thus allowing fluorescent signals to be quantified from whole animals. << /Length 5 0 R /Filter /FlateDecode >> Group 6: Explain the data shown in figure 4 in the accompanying article, including the reason the authors collected these data. These genes are thus termed “suppressors of the lin-35; slr-2 synthetic lethal phenotype.” Remember that suppression is seen only when the product of the suppressor gene is downregulated or missing. 17, 2108-17. Again, the suppressor screen identifies another component in the same circuit. Average numbers of GFP signals/worm are integrated into a database and subjected to statistical analysis. Pick out several interesting points that you can interpret for the class. The figures are quite accessible to undergraduate students; it is the connection to molecular and cellular mechanisms of suppression that will require repetitive explanation. Alert readers will have realized that larval lethality is a pretty difficult phenotype with which to work. Be prepared to defend your answer using the data provided. Removal of the bracket allows the switch to automatically pop into the “on” position. 53, 1407-11. It has been studied in the laboratory since the 1970s, where it also feeds on bacteria. This approach is called a “suppressor screen.”. One classic example is the let-60 (gf) suppressor screen carried out in recent years by the Han lab. By undertaking RNAi of a suppressor gene in worm strains that contain the lin-35; slr-2 mutations plus a null allele of another known suppressor, Polley and Fay determined whether reductions of suppressor proteins have additive effects. In this metaphor, the bracket could be a repressor of a gene or a negative regulator of a protein function. Because they knew which gene is targeted by the double-stranded RNA in each bacterial strain in the RNAi library, they automatically knew which gene is the (putative) suppressor of lin-35; slr-2 larval arrest. Morphometric analysis of images (here 2048x2048) is performed using Image J and a script developed in the laboratory. (2007) in which students sequentially read several articles from one lab, a useful sequence would be Fay et al. J. Med. How might you interpret these data? How did Polley and Fay confirm that their results were both significant and then biologically meaningful? Our members work to advance knowledge in the basic mechanisms of inheritance, from the molecular to the population level. What other genes and proteins are directly or indirectly involved in processes with lin-35? In what cellular or organismal process is lin-35 involved? Julie Ahringer and co-workers designed an RNAi library—a set of bacterial strains each expressing a different double-stranded RNA molecule, one strand of which is complementary to mRNA encoded by a single C. elegans gene (Fraser et al. 1A). Polley and Fay mention a forward genetic screen (from phenotype > gene) undertaken in previous work and describe a reverse genetic screen (from gene > phenotype) using RNAi. Kirienko and co-workers demonstrated that LIN-35 and SLR-2 have redundant functions in the intestine because intestinal deficiency is seen only in double-mutant animals (another synthetic phenotype). Polley and Fay studied the role of a transcriptional regulator called Rb in mammals and LIN-35 in C. elegans. to use double-stranded RNA to degrade other RNAs as an antiviral response (Wilkins et al. They then looked for non-green offspring (that lost the gene array) that survived beyond the L1 larval stage. This kind of suppressor screen is therefore a way to identify genes whose products function together in the same pathway or in compensatory pathways. Suppressor genetics Reading: lecture notes Screens 1.Direct screen: phagocytosis and apoptotic genes in C. elegans 2.Mosaic screen: tumor suppressor genes 3.Revertant screens wild type mutant mutagen Forward and reverse mutations mutant revertant (wild type or more wild type) forward reverse Donʼt confuse reverse mutations