Oosp1 encodes a novel mouse oocyte-secreted protein

Oocyte-somatic cell communication is necessary for normal ovarian function. However, the identities of the majority of oocyte-secreted proteins remain unknown. A novel cDNA encoding mouse oocyte-secreted protein 1 (OOSP1) was identified using a modified subtractive hybridization screen. The Oosp1 cDNA encodes a 202-amino acid protein that contains a 21-amino acid signal peptide sequence, 5 putative N-linked glycosylation consensus sequences, and 6 cysteines that are predicted to form 3 disulfide bonds. OOSP1 shares amino acid identity with placental-specific protein 1 (PLAC1), a secreted protein expressed in the placenta and the ectoplacental cone. The Oosp1 mRNA is approximately 1.0 kb and is present at high levels in the oocytes of adult ovaries and at lower levels in the spleen. The mouse Oosp1 gene is 5 exons, spans greater than 16.4 kb, and localizes to chromosome 19 at a position that shares synteny with human chromosome 11q12-11q13. The identification of OOSP1 as a new oocyte-secreted protein permits future in vitro and in vivo functional analyses to define its role in ovarian folliculogenesis.