Woodhouse, Rachel et al. (2019) International Worm Meeting "Transgenerational epigenetic inheritance is revealed as a multi-step process by studies of the SET-domain proteins SET-25 and SET-32."

Ashe, Alyson, Low, Jason, Larance, Mark, Woodhouse, Rachel, Buchmann, Gabriele, Boag, Peter, Harney, Dylan, Hoe, Matthew

[International Worm Meeting, 2019]

It has recently become clear that in some circumstances Lamarck may have been right. There are a growing number of examples where a clear case can be made for the inheritance from parent to offspring of environmentally acquired gene expression changes. We have developed a sensor in C. elegans in which RNAi-induced silencing of a GFP transgene is robustly inherited for multiple generations in the absence of the initial RNAi trigger. The visible nature of this phenotype provides an exquisitely sensitive system, whereby we can separate individual animals according to their silencing status and measure effects in these distinct groups. Using this approach, we show that the histone H3 lysine 9 (H3K9) trimethyltransferase SET-25 and the putative histone methyltransferase SET-32 are required in the RNAi-exposed generation for effective transmission of transgene silencing, but are dispensable for silencing inheritance in subsequent generations. This indicates that SET-25 and SET-32 are required for the establishment of a transgenerational silencing signal but not for long-term maintenance of this signal, suggesting that transgenerational epigenetic inheritance is a multi-step process with distinct genetic requirements for establishment and maintenance of heritable silencing. We further characterize SET-25 and SET-32 to gain insights into the nature of the silencing establishment signal. We show that SET-25 is expressed in nuclei in the mitotic zone and embryos, whilst SET-32 is expressed in both the cytoplasm and nuclei throughout the entire germline. Additionally, immunofluorescence and quantitative mass spectrometry reveal aberrant H3K9me3 in set-25 and set-32 mutants. Previous studies have implicated secondary siRNAs as the effector molecules of heritable silencing. We separated animals according to their inherited silencing status (GFP-silenced or GFP-expressing) and sequenced small RNA populations in set-25 and set-32 mutants, and in mutants of the nuclear RNAi inheritance machinery. We found that the abundance of secondary siRNAs does not correlate well with silencing phenotypes in the sequenced generation or in the next generation, suggesting that the current mechanistic models of epigenetic inheritance are incomplete.

Gabriele Gahmon et al. (2006) European Worm Meeting "Ectopic Expression of DAF-19, a Transcription Factor that Controls Cilium Development"

Peter Swoboda, Gabriele Gahmon

[European Worm Meeting, 2006]

Gabriele Gahmon and Peter Swoboda. DAF-19 is an RFX-transcription factor (Regulatory Factor binding to the X-box), which has been shown to be essential for the development of cilia on 60 sensory neurons in C. elegans. Mutations in daf-19 lead to the complete loss of all ciliated structures, but leave the cell bodies and neurites of these neurons intact. DAF-19 has been shown to regulate a large number of cilium-specific genes encoding structural and functional cilium components as well as other transcription factors. This finding suggests a very central role of DAF-19 during ciliogenesis. Since DAF-19 is essential for the formation of cilia, we hypothesize that it could also be sufficient. We try to answer this question by expressing the daf-19 gene from heterologous promoters in cells that usually do not carry cilia with the aim of inducing ectopic cilia. When expressed in tail hypodermis cells, daf-19 leads to morphological changes of the hermaphrodite tail and to the ectopic expression of direct DAF-19 target genes. Several of these cells do not show hypodermal cell characteristics anymore, but display more neuron-like features (e.g. processes). Currently we are characterizing in detail to what extent the ectopic expression of daf-19 can transform hypodermis cells into neuronal or even cilium-carrying cells.