Expression of beta-subunit of HCG genes during normal and failed pregnancy

One of the first proteins synthesized by a conceptus is HCG. The receptor-binding beta-subunit of HCG (HCGbeta) is encoded by highly homologous CGB, CGB5, CGB7 and CGB8 genes. The function of two additional gene copies, CGB1 and CGB2, is still unknown. We aimed to compare the expression of individual CGB genes during normal pregnancy and in cases of recurrent miscarriage (RM) and ectopic pregnancy (EP).

A semiquantitative RT-PCR with fluorescent-labelled primers coupled with the gene-specific restriction and quantification was used.

The summarized expression of HCGbeta genes was high throughout the pregnancy, and moderately correlated with HCG in serum. In cases of RM, reduced hormone values were consistent with low mRNA levels, whereas for EP no reduction in transcriptional activity was detected. CGB1and CGB2 showed a considerable expression peak during the first trimester, both in normal and ectopic pregnancy, but not for RM.

In cases of RM, low HCG could result from expression failure of HCGbeta genes, whereas in EP the problems other than the transcriptional failure contribute to reduced hormone levels. The expression patterns of CGB1 and CGB2 suggest their putative role in the implantation stage.