Epigenetic Silencing of Nuclear Transgenes in Chlamydomonas

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Cerutti 9808473It has recently been demonstrated in this laboratory that epigenetic transcriptional inactivation occurs in algae as well as in higher plants. In Chlamydomonas, two mechanisms, namely chromatin/nuclear domains and DNA methylation, are hypothesized to be the responsible mechanisms. In order to test these working hypotheses, this project has the following specific aims: 1) To isolate tagged mutants defective in transcription gene silencing, 2) To clone and characterize a tagged gene(s) involved in transcription repression, and 3) To map the chromosomal location of silenced and stable transgenic loci.The production of transgenic plants and animals is rapidly becoming routine, but the introduced genes are often unstably expressed, leading to the loss or reduced manifestation of newly acquired traits. This phenomenon of transgene silencing often results from a variety of epigenetic mechanisms, operating at both transcriptional and post-transcriptional levels. In most cases the underlying molecular processes have not been precisely identified. The results of this work could contribute to a greater understanding of epigenetic phenomena in eukaryotes, since preliminary data suggest that the molecular mechanisms might be evolutionarily conserved. The analysis of epigenetic gene silencing in Chlamydomonas can provide a genetic approach for understanding essential features of chromosomal/nuclear organization controlling gene expression. From a practical perspective, the results could contribute to the development of methods to overcome epigenetic silencing methodology, which could contribute to the generation of transgenic plants and animals.