College of Science and Health Theses and Dissertations

Zygote gene expression and plasmodial development in Didymium iridis

Sean Scaefer, DePaul University


Didymium iridis is a cosmopolitan species of plasmodial slime mold consisting of two distinct life stages. Haploid amoebae and diploid plasmodia feed on microscopic organisms such as bacteria and fungi through phagocytosis. Sexually compatible haploid amoebae act as gametes which when fused embark on an irreversible developmental change resulting in a diploid zygote. The zygote can undergo closed mitosis resulting in a multinucleated plasmodium. Little is known about changes in gene expression during this developmental transition. Our principal goal in this study was to provide a comprehensive list of genes likely to be involved in plasmodial development. We performed suppressive subtractive hybridization to create cDNA libraries enriched for zygote or plasmodial specific genes. The cDNA libraries were then cloned and sequenced. The sequences were used to search against GenBank gene databases to identify related sequences and characterized proteins. We have compiled a list of candidate genes likely to be involved in the amoebae-zygote transition and have arranged them by their known or predicted function. Genes related to cytoskeletal structure, cell signaling, ubiquitin-proteasome pathways, mitochondrial inheritance, and DNA binding proteins were of particular interest due their possible role in this developmental transition. Selected gene sequences were also tested for differential expression by dot blot and RT-PCR.