A novel change in cytologic localization of human chorionic gonadotropin and human placental lactogen in first-trimester placenta in the course of gestation

Cytologic localization of human chorionic gonadotropin and human placental lactogen in developing human early placenta was analyzed by avidin-biotin immunoperoxidase techniques with an affinity-purified polyclonal antibody to β-human chorionic gonadotropin carboxyl terminal peptide and a polyclonal antibody to human placental lactogen. In 4- to 5-week placentas human chorionic gonadotropin and human placental lactogen were found to be primarily localized to cytotrophoblasts, whereas in 6- to 12-week placentas these substances were exclusively localized to syncytiotrophoblast. We previously reported that a similar change in cytologic localization of epidermal growth factor and its receptor from cytotrophoblasts to syncytiotrophoblast in first-trimester placenta appeared between 5 and 6 weeks of gestation. Because epidermal growth factor was demonstrated to stimulate human chorionic gonadotropin and human placental lactogen production by early placental tissues, their simultaneous expression, as well as epidermal growth factor and its receptor in the cytotrophoblast of 4- to 5-week placenta and in the syncytiotrophoblast of 6- to 12-week placenta, implies that human chorionic gonadotropin and human placental lactogen production by first-trimester placenta may be regulated in an autocrine manner, wherein epidermal growth factor may serve as the signal. These findings suggest that in very early placenta, before 6 weeks of gestation, no sequential expression of human chorionic gonadotropin and human placental lactogen closely linked to syncytia formation may exist and that both can be expressed in the cytotrophoblast or undifferentiated stem cell of villous trophoblast in very early placenta.