Characterization of baboon pregnancy-specific beta 1-glycoprotein

Immunostaining of baboon placental tissues with anti-human pregnancy-specific beta 1-glycoprotein (SPI) antibodies demonstrated that an SP1-like molecule was present in the syncytiotrophoblasts. Staining was observed on the membrane and in the cytoplasm, but the nucleus was devoid of any staining. Western blot analysis further demonstrated the presence of five protein species in baboon placental extract, whereas four protein bands were detected in human placental extract. Culture medium of baboon placental villi also contained five SP1-like molecules with sizes slightly different from those present in the placental extract. Amniotic fluid and culture medium of decidua basalis and chorioamniotic tissue contained lesser quantities and fewer species of SP1-like molecules. However, an 87 kDa band was present in all samples examined. Northern blot analysis of baboon placenta with a human placental SP1 cDNA probe demonstrated the presence of a 1.65 Kb band, whereas two hybridizing bands (1.65 Kb and 2.25 Kb) were present in human placenta. Southern blot analysis of baboon genomic DNA further demonstrated the presence of multiple bands hybridizing with a human placental SP1 cDNA probe. These results showed the presence in baboons of multiple genes encoding mRNAs and proteins highly similar to human placental SP1.