Keunhee Park et al. (2005) International Worm Meeting "A genetic screen for factors mediating the interaction between PIE-1 and the LET-418 complex"

Prashant Raghavan, Keunhee Park, Seung-il Kim, Tae Ho Shin, Byung-Jae Park, Stacy Lloyd, Jungsoon Lee, Hosung Shim

[International Worm Meeting, 2005]

We previously reported a genetic screen to identify factors that mediate the repressive interaction between the germline-specific protein PIE-1 and a putative chromatin remodeling activity, the LET-418/HDA-1/MEP-1 complex (ECWM 2004, Abstract 206). The screen is a suppressor screen and relies on two observations; (a) the LET-418 complex functions in the synMuvB pathway and (b) ectopic expression of PIE-1 in the somatic cells results in a penetrant multivulva (Muv) phenotype, presumably due to the downregulation of the LET-418/HDA-1/MEP-1 activity.We have analyzed approximately 20,000 mutagenized haploid genomes and isolated 73 mutants that show strong suppression of the Muv defect caused by PIE-1 expression. These mutants appear to fall into a large number of complementation groups (34 or more) but can be categorized into several distinct classes based on the phenotype. First, when one of the synMuvB components, MEP-1, LIN-35 or LIN-36, is downregulated by RNAi, only 18 mutants can suppress the resulting Muv phenotype regardless of the component being targeted. In contrast, 52 mutants show either no suppression or a measurable bias toward one or two components of the synMuvB pathway. Second, a large portion of the suppressors (at least 31 mutants) is hypersensitive to RNAi. For example, mutants ex88, ex107 and ex108 require as little as 1/10 of the RNAi-inducing bacteria to achieve the same degree of phenotype (50% penetrance) as defective in the production of tncRNAs, suggesting that tncRNAs may mediate the function of PIE-1 or the LET-418/HDA-1/MEP-1 complex or both.

Kelly WG (2000) East Coast Worm Meeting "Parent of Origin Effects in C. elegans: Worm Imprinting or an Insight Into Hybrid Dysgenesis?"

Kelly WG

[East Coast Worm Meeting, 2000]

Parent of origin effects in gene expression describe how the sex of a parent transmitting a particular allele affects the expression of that gene in its offspring. A gene that exhibits a differential expression in the offspring that depends on whether it was inherited from the mother or the father is considered to be imprinted. Imprinting has been shown in mammals to closely correlate with cytosine methylation, yet parent of origin effects have been frequently reported in Drosophila, an organism in which methylated cytosine is not observed (e.g. Lloyd et al, Genetics 151:1503). Imprinting in C. elegans has previously been investigated by looking at cross-progeny that were homozygous for a single chromosome from either parent, using him-6 to generate disomic or nullisomic gametes in each cross (Haack and Hodgkin, Mol.&Gen. Genet 228:482). No effects on viability were observed, leading to the conclusion that either chromosomal imprinting effects do not occur in the worm, or that their effects are minor. C. elegans also has no detectable methylcytosine. During crosses to build transgenic strains for testing germline desilencing, a high frequency of transient activation of silenced transgenes was observed in the germ cells of the offspring. Upon further investigation it was shown that this activation only occurs when the silenced transgene is inherited from the father, and the effect is temperature-sensitive. The activation is generally restricted to the F1 progeny, although a low frequency of heritable activation can be observed. Interestingly, the presence of a transgene in the recipient oocyte that bears partial homology to the incoming reporter suppresses the activation of the reporter. This suppression is still seen in animals arising from oocytes that have lost the suppressing DNA during meiosis. The effect of different mutations on this phenomenon, its applicability for germline transgene expression protocols, and its natural role in worm biology will be discussed.