FIG alpha, a germ cell-specific transcription factor required for ovarian follicle formation

Primordial follicles are formed perinatally in mammalian ovaries and at bir th represent the lifetime complement of germ cells, With cyclic periodicity , cohorts enter into a growth phase that culminates in ovulation of mature eggs, but little is known about the regulatory cascades that govern these e vents. FIG alpha, a transcription factor implicated in postnatal oocyte-spe cific gene expression, is detected as early as embryonic day 13, Mouse line s lacking FIG alpha were established by targeted mutagenesis in embryonic s tem cells. Although embryonic gonadogenesis appeared normal, primordial fol licles were not formed at birth, and massive depletion of oocytes resulted in shrunken ovaries and female sterility. Fig alpha (the gene for FIG alpha ) null males have normal fertility. The additional observation that null fe males do not express Zp1, Zp2 or Zp3 indicates that FIG alpha plays a key r egulatory role in the expression of multiple oocyte-specific genes, includi ng those that initiate folliculogenesis and those that encode the zona pell ucida required for fertilization and early embryonic survival. The persiste nce of FIG alpha in adult females suggests that it may regulate additional pathways that are essential for normal ovarian development.