Schickler, M., Cell/Developmental Biol. Dept., Roche Molecular Biology Inst., Roche Research Center, Nutley, NJ 07110, United States
Lira, S.A., Cell/Developmental Biol. Dept., Roche Molecular Biology Inst., Roche Research Center, Nutley, NJ 07110, United States
Kinloch, R.A., Cell/Developmental Biol. Dept., Roche Molecular Biology Inst., Roche Research Center, Nutley, NJ 07110, United States
Wassarman, P.M., Cell/Developmental Biol. Dept., Roche Molecular Biology Inst., Roche Research Center, Nutley, NJ 07110, United States

The gene encoding mZP3, the mouse sperm receptor, is expressed exclusively in growing oocytes during oogenesis. To investigate the molecular basis of oocyte-specific mZP3 gene expression, we generated several lines of mice harboring a transgene that contains 470 bp of mZP3 gene 5'-flanking sequence (nucleotides -470 to +10) fused to the firefly luciferase gene coding region. Three of four expressing transgenic lines exhibited luciferase activity only in growing oocytes, suggesting that the 470-bp fragment is sufficient to direct oocyte-specific expression of the luciferase gene. Results of DNase I footprinting and gel mobility shift assays suggested the presence of an ovary-specific protein that binds to a small region (nucleotides -99 to -86) within the 470-bp fragment of the mZP3 promoter, with 5'-G(G/A)T(G/A)A-3' representing the minimal sequence required for binding. Southwestern (DNA- protein) gel blots revealed the presence of an oocyte-specific, ~60,000-M(r) protein, called OSP-1, that binds to the minimal sequence. Changes in levels of OSP-1 during oogenesis and early cleavage are consistent with the pattern of mZP3 gene expression during these developmental stages in mice. Therefore, OSP-1 may be a mammalian oocyte-specific transcription factor involved in regulating oocyte-specific mZP3 gene expression.