FIG-ALPHA, A GERM-CELL SPECIFIC TRANSCRIPTION FACTOR INVOLVED IN THE COORDINATE EXPRESSION OF THE ZONA-PELLUCIDA GENES

The mouse zona pellucida is composed of three glycoproteins, ZP1, ZP2 and ZP3, encoded by single-copy genes whose expression is temporally a nd spatially restricted to oocytes. All three proteins are required fo r the formation of the extracellular zona matrix and female mice with a single disrupted zona gene lack a zona and are infertile. An E-box ( CANNTG), located approximately 200 bp upstream of the transcription st art sites of Zp1, Zp2 and Zp3, forms a protein-DNA complex present in oocytes and, to a much lesser extent, in testes. It has been previousl y shown that the integrity of this E-box in Zp2 and Zp3 promoters is r equired for expression of luciferase reporter genes microinjected into growing oocytes, The presence of the ubiquitous transcription factor E12 in the complex was used to identify a novel basic helix-loop-helix protein, FIG alpha (Factor In the Germline alpha) whose expression wa s limited to oocytes within the ovary. The ability of FIG alpha to tra nsactivate reporter genes coupled to each of the three mouse zona prom oters in heterologous 10T1/2 embryonic fibroblasts suggests a role in coordinating the expression of the three zona pellucida genes during o ogenesis.