Pukkila 9603792 The source of specificity for meiotic chromosome pairing is not known. We have shown that prior to meiosis, a genome-wide homology search occurs in haploid nuclei of Coprinus cinereus which results in the methylation of duplicated sequences, a process termed MIP (methylation induced premeiotically). We have also shown that a mutation with defects in meiotic synapsis, (bad27) is deficient in MIP. Thus it appears that either prior MIP is essential for synapsis, or that MIP and meiotic pairing are genetically related. We are utilizing MIP to analyze the genetic basis of homologue recognition. We have isolated four mutants which arrest in meiotic prophase following nuclear fusion (karyogamy) with decondensed chromosomes that exhibit very limited axial core formation (class I synaptic defect). We have also isolated six mutants which arrest with condensed univalents (class II synaptic defect). We have shown that one of the class II mutants (bad27) is deficient in MIP. We will ask if the class I mutants and the other class II mutants can carry out MIP. We will use serial sectioning and 3-dimensional reconstruction to learn if homologue alignment occurs normally in the class II mutants. We will determine epistatic relationships among the class I and class II mutants. By ordering these genes in a genetic pathway, we should begin to establish cause and effect relationships among them. Finally, we will utilize DNA-mediated transformation to obtain a cloned DNA sequence that can complement the defects in MIP and synapsis conferred by the bad27 mutation. These studies should provide unique insights into the underlying mechanisms of homologue recognition. This research will help us understand how a process that is almost universal in plants and animals occurs. This process is called meiosis, and involves the pairing of chromosomes inherited from both parents so that reproductive cells can be formed (such as sperm and eggs). Dr. Pukkila is studying a fungus which she has s hown provides special advantages for uncovering the steps that occur in this process.
