Transcription patterns of hCG beta-subunit during normal and failed pregnancy
One of the first proteins synthesized by conceptus is human chorionic gonadotropin (hCG). Besides its luteotropic function hCG regulates implantation and immunomodulation at maternal-fetal interface. Low level of hCG is related to miscarriage, ectopic pregnancy and failure of assisted reproduction procedures. Critical for hCG assembly and production rate is the beta-subunit of the hormone. Six CGB (chorionic gonadotropin beta) genes share the common gene cluster with LHB gene at 19q13.3. Whereas CGB, CGB5, CGB7 and CGB8 express hCG-beta, the function of CGB1 and CGB2 coding for a hypothetical protein, is still unknown. We explored the expression profile of all CGB genes in normal and failed pregnancies using semiquantitative RT-PCR (references GAPDH and RPII) combined with gene-specific restriction facilitating identification of mRNA products specific to each CGB gene. Blood and chorionic villi/placental samples were collected from females at every trimester of normal pregnancy; and from patients who underwent surgical evacuation of gestation from (i) uterine cavity because of recurrent miscarriage; or (ii) tuba due to extrauterine pregnancy. When adjusted to gestational age, the expression of CGB genes was at the same level in normal and ectopic pregnancy. However, the transcription of CGB-s was significantly lower in cases of recurrent miscarriages. We postulate a hypothesis that certain CGB variants or rearrangements of this complex genomic region might be responsible for the reduction in the transcription level of these genes. Furthermore, to overcome the maternal-fetal conflict the genes involved in implantation, might be paternally imprinted. The study aiming to bring light into this issue concerning CGB genes is in progress.