Identification of differentially expressed genes in human trophoblast cells by differential-display RT-PCR

Molecular mechanisms controlling human trophoblast invasiveness are still poorly understood. In the present investigation, mRNA patterns of trophoblast cells isolated from first trimester (high invasiveness) and term placentae (no/low invasiveness) were compared by differential-display reverse transcriptase polymerase chain reaction (DDRT-PCR) revealing differential expression of numerous genes. Of 18 differentially expressed DDRT-PCR products analysed, 11 were unknown, four showed homologies with expressed sequence tag sequences, and three others were homologous to integrin-beta1, ATP-synthetase U6 (both showing higher expression in first trimester) or to aldose-reductase (higher expression at term), respectively. One of the unknown transcripts (PBK1, accession number: AJ007398) was cloned from a first trimester placenta cDNA library and was characterized. The 1908-bp gene fragment contains an open reading frame of 1551 bp and an Alu-sequence in the 3' non-coding region. According to Northern blot analysis on JAr choriocarcinoma cells, the fragment is close to full-length cDNA. By in situ hybridization, PBK1 was detected only in first trimester but not term placentae in the proximal parts of cell islands and in closely adjacent villous cytotrophoblast. This expression pattern suggests that the newly identified molecule, PBK1, could be involved in the regulation of proliferation/ differentiation and potentially in invasion of trophoblast cells.