Fig. 4. KiSS-1/Kp-54 and KiSS-1R localization in first trimester placenta. Sections of human FT placental tissue at week 6-10 of gestation showing the localization of KiSS-1/Kp-54 (A,B) and KiSS-1R (E,F). KiSS-1 and KiSS-1R mRNA were detected by in situ hybridization as dark blue precipitates, whereas their respective proteins were detected using affinity purified polyclonal antibodies evident as dark red precipitate. Sense probes (C,G) and nonimmune sera (D,H) produced no detectable signal. KiSS-1 mRNA (A) and Kp-145/Kp-54 protein (B) were detected mainly on the outer (syncytiotrophoblast) surface of villi. Higher magnification showed that KiSS-1/Kp-54 expression is restricted to the syncytiotrophoblast (insets; A and B; bars, 25 µm), whereas it was undetectable in villous (vCT) and extravillous (evCT) cytotrophoblasts. KiSS-1R mRNA is located in the syncytiotrophoblast (ST), villous (vCT) and extravillous (evCT) cytotrophoblasts (E). This mRNA staining pattern is paralleled by that of KiSS-1R protein (F). Bars, 50 µm.