9506262 Straus The goal of Dr. Straus' work is to understand how totipotency, the ability to undergo embryogenesis, is restricted to a specific subset of embryonic cells in Volvox carteri. Volvox is ideal for dissecting the mechanisms underlying the regulation of totipotency because it is composed of only two cell types: germ line and somatic. Furthermore, the entire pathway that determines cell fate is accessible to genetic and biochemical analysis. Volvox individuals have about 16 germ line cells that are specialized to undergo embryogenesis and about 2,000 somatic cells that provide motility and never divide. During embryogenesis, a single large germ line cell undergoes rapid cleavage divisions to form a 2,000 celled embryo. The embryonic blastomeres then differentiate in a reproducible lineage dependent manner into somatic cells and germ line cells. The specialized somatic and germ line phenotypes are ultimately due to the differential expression of cell type specific gene sets. Dr. Straus' laboratory is cloning a gene, regA, that is needed for correct cell type specific gene expression and cell fate determination. In regA minus mutants somatic cells ectopically express the gene set that normally is confined to the germ line in addition to expressing the normal somatic cell repertoire. The somatic cells of these mutants redifferentiate into totipotent germ line cells. During the previous funding period Dr. Straus localized the regA gene to a small chromosomal region using Targeted RFLP Subtraction, a powerful and general method he developed for isolating genes defined by mutations. He proposes to complete the physical characterization of the regA locus and to isolate the gene from the region. Cloning the gene will allow him to investigate the role of regA in limiting totipotency and to learn how the processes of cell fate determination and cell differentiation are integrated in Volvox. ***
