Human chorionic somatomammotropin gene expression in primary placental cell cultures

Mono-nucleated cytotrophoblasts (cytoTBs) were prepared by Percoll gradient fractionation of enzymically disaggregated human placental tissue. These cells were plated in monolayer culture in the presence of fetal calf and calf serum. Within 2-24 h, the cytoTBs aggregate, and by 48 h, they are clearly fused into multinucleated syncytia. The presence of human chorionic somatomammotropin (hCS) and chorionic gonadotropin (hCG) in the cells after 48 h was determined by immunohistochemistry. To assess whether hCS is synthesized in our cultures we examined hCS mRNA accumulation with time. The presence of hCS mRNA was detected at the time of plating but full length transcripts were seen only at later times indicating synthesis in culture. However, preparations at the time of plating contain fragments of syncytiotrophoblast (syncytioTB) generated by enzymic or mechanical disaggregation. These fragments could fuse with the cytoTBs. The inclusion of these fragments makes analysis of placental hormones by protein detection an unreliable assay for synthesis. Analysis of mRNA levels support hCS synthesis in culture and correlates with aggregation and fusion of cytoTBs. Thus, the fused cells in culture mimic the cellular site of hCS synthesis in vivo, the syncytioTB.