FUNCTIONAL-DIFFERENTIATION OF PLACENTAL SYNCYTIOTROPHOBLASTS DURING BABOON PREGNANCY - DEVELOPMENTAL EXPRESSION OF CHORIONIC SOMATOMAMMOTROPIN MESSENGER-RIBONUCLEIC-ACID AND PROTEIN-LEVELS

The objective of the present study was to determine whether, in additi on to the onset of chorionic somatomammotropin (CS) production previou sly shown to result from the morphological differentiation of cytotrop hoblasts into syncytiotrophoblasts, there is a further developmental i ncrease in the capacity of syncytiotrophoblasts to produce CS with adv ancing stages of baboon pregnancy. Placentas were obtained from baboon s in early (days 48-62), mid (days 97-110), and late (days 161-175) ge station (term = 184 days), and CS messenger ribonucleic acid (mRNA) an d protein levels were determined in a syncytiotrophoblast-rich cell fr action isolated by Percoll gradient centrifugation. CS mRNA levels in syncytiotrophoblasts, expressed as a ratio of p-actin, exhibited a pro gressive increase from early (0.04 +/- 0.04 relative arbitrary units) to mid (2.37 +/- 0.33; P < 0.001) to late (3.66 +/- 0.39; P < 0.05) ge station. Levels of the 22-kDa CS protein were very low on days 48-55 ( 0.83 +/- 0.09 arbitrary units), increased 10-fold (P < 0.001) on days 57-60 (8.11 +/- 0.68), and increased (P < 0.001) to a maximum of 14.58 +/- 0.58 near term. CS mRNA levels in whole placental villous tissue increased (P < 0.05) between early (0.89 +/- 0.48) and mid (2.97 +/- 0 .47) gestation, then remained constant. CS protein exhibited a similar increase (P < 0.001) in villous tissue between early (2.32 +/- 0.40) and mid (6.07 +/- 0.24) gestation, then remained constant. The increas e in mRNA and protein levels of CS in the placenta was accompanied by a progressive (P < 0.001) rise in serum CS. We conclude that in additi on to the morphological differentiation of cytotrophoblasts into syncy tiotrophoblasts that has been well established to result in the onset of CS biosynthesis, villous syncytiotrophoblasts undergo functional/bi ochemical differentiation thereafter, manifested as an increase in the capacity for the synthesis of CS.