Ubiquitin and ubiquitin-protein conjugates are present in human cytotrophoblast throughout gestation.

Ubiquitin is a small protein involved in many intracellular processes. We have previously shown that levels of ubiquitin change during the process of decidualisation in the human uterus at the beginning of pregnancy. Other workers have shown that the ubiquitin system may be essential for normal murine placental development. In this investigation we employed immunohistochemistry and immunoblotting techniques to study the distribution and abundance of ubiquitin and ubiquitin-protein conjugates within human placental specimens from throughout gestation. Trophoblast from two pathological conditions, ectopic pregnancy and pregnancy-induced hypertension (PIH), was also investigated. Ubiquitin was detected within both the cytoplasm and nucleus of the cytotrophoblast layer only. Both monomeric and conjugated forms of ubiquitin were detected. The relative abundance of ubiquitin did not change through gestation or in the two disorders of pregnancy studied. Ubiquitin cross-reactive protein was not detected in the tissues of interest. This is the first report to demonstrate the cell-specific localisation of ubiquitin and ubiquitin-protein conjugates in the human cytotrophoblast and provides supportive evidence that ubiquitin may be important during placental development.