Two distinct aspects of sexual development in Neurospora crassa: Peroxisomal function and gene silencing.

摘要

While the filamentous ascomycete, Neurospora crassa has been studied for almost a century, there is still little known about the genetic control of the sexual cycle. Sexual mutations have been characterized phenotypically, but many of the genes responsible for those mutations have yet to be discovered. This dissertation centers around characterization of the role of peroxisomes, fatty acids and gene silencing in the sexual cycle. Specifically, the identification and molecular characterization of genes is reported.; A study of the fatty acid content in the three stages of the life cycle show that fatty acid composition of Neurospora cultures competent for sexual development differs substantially from the composition of cultures during asexual development. In addition, the fatty acid composition of developing asci is distinct from that of the asexual supporting tissue of the fruiting body. The lipid composition of ascospores is also distinct from both types of asexual spores formed by Neurospora. Both polar lipids and triacylglycerols undergo significant changes in amount or composition during several stages of sexual development, indicating that major changes in lipid metabolism correlate with specific developmental events. The peroxisome assembly gene of N. crassa, pex2 (peroxin-2), was then cloned, sequenced and initially characterized due to the obvious significance of the metabolism of fatty acids during sexual development. Results reported in this study indicate that pex2 is probably an essential gene, required for normal peroxisomal function.; In contrast to work on fatty acids and peroxisomes, this study also investigates the role of post-transcriptional gene silencing (PTGS) in sexual development. The asd-2 (ascus development-2) gene is a member of the Argonaute family of proteins, known to be involved in PTGS. The ASD2 protein is essential for sexual development in N. crassa as sexual development is aborted in homozygous asd-2 mutant crosses. Experiments indicate no role for ASD2 in the known types of PTGS of N. crassa, quelling and meiotic silencing of unpaired DNA (MSUD).