The goal of this proposal is to understand how totipotency, the ability to undergo embryogenesis, is restricted to a single cell lineage in the eukaryote Volvox carteri. Volvox is ideal for dissecting the mechanisms underlying the regulation of totipotency since it is composed of only two types of cells: reproductive and somatic. In asexual (clonal) growth, reproductive cells cleave successively yielding a new embryo while somatic cells never divide. A number of mutants that alter cell fate have defined critical genes in the determination pathway. In regA - mutants, somatic cells redifferentiate into reproductive cells and become totipotent. The locus is unusual in that it becomes hypermutable (105 times the spontaneous rate) at a specific stage in development. The primary aim is to determine how the regA gene normally keeps the somatic cell lineage from undergoing embryogenesis and why it is transiently hypermutable. The PI has devised two powerful new methods to isolate the regA gene: genomic subtraction and DAF (differentially amplified fragment) subtraction. To begin to understand how regA regulates totipotency, cloned gene will be used in studies to determine the nature of the regA gene product and the molecular basis for the unusual hypermutability of the gene.
